Tag Archives: High Energy Physics – Theory

Constraints on the scalar inflation from preheating of LATTICEEASY [CEA]

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http://arxiv.org/abs/2212.12851


In this paper, we study scalar inflation in detail by applying the preheating of LATTICEEASY simulation. In general, scalar inflation potential with non-minimal coupling can be approximated to the quartic potential inflation. We observe that the evolutionary trend of this potential is independent of the coupling coefficient, and theoretical predictions for the scalar spectral index $n_s$ and tensor-to-scalar power ratio $r$ are also independent of the coefficient, which implies that the coefficients of this model will not be bounded by the Planck observations. Fortunately, the properties of preheating after inflation provide a feasible scheme to study those coefficients. For the preheating process, the evolution of particle number density, scale factor, and energy density can be restored and tracked by applying LATTICEEASY simulation, then the parameters energy ratio $\gamma$ and the e-folding number of preheating $N_{pre}$ will be deduced, and the $n_s$ and $r$ can be further predicted. We have tested the scalar inflation model by the preheating nature of LATTICEEASY based on the analytical relationship between preheating and inflation models.

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W. Cheng and T. Qin
Tue, 27 Dec 22
22/30

Comments: 13 pages, 6 figures

The causality road from dynamical triangulations to quantum gravity that describes our Universe [CL]

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http://arxiv.org/abs/2212.13109


It is shown how one, guided by causality, starting from so-called dynamical triangulations, is led to a candidate of quantum gravity that describes our Universe. This theory is based on W- and Jordan algebras. It explains how our Universe was created, how cosmic inflation began and ended, how the topology and the geometry of our Universe was formed, and what was the origin of Big Bang energy. The theory also leads to a modified Friedmann equation which explains the present accelerating expansion of our Universe without appealing to the cosmological constant.

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Y. Watabiki
Tue, 27 Dec 22
27/30

Comments: This is a contribution to the Handbook of Quantum Gravity which will be published in 2023. It will appear as a chapter in the section of the handbook denoted “Causal Dynamical Triangulations”

Building cubic gravity with healthy and viable scalar and tensor perturbations [CL]

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http://arxiv.org/abs/2212.12494


We investigate the conditions under which cubic gravity is healthy and viable at the perturbation level. We perform a detailed analysis of the scalar and tensor perturbations. After showing that no instabilities appear, we impose the requirement that the two scalar potentials, whose ratio is the post-Newtonian parameter $\gamma$, should deviate only minimally form general relativity. Additionally, concerning the tensor perturbations we impose satisfaction of the LIGO-VIRGO and Fermi Gamma-ray Burst observations, and thus we result to a gravitational-wave equation with gravitational-wave speed equal to the speed of light, and where the only deviation from general relativity appears in the dispersion relation. Furthermore, we show that cubic gravity exhibits an effective Newton’s constant that depends on the model parameter, on the background evolution, and on the wavenumber scale. Hence, by requiring its deviation from the standard Newton’s constant to be within observational bounds we extract the constraints on the single coupling parameter $\beta$.

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P. Asimakis, S. Basilakos and E. Saridakis
Mon, 26 Dec 22
4/39

Comments: 9 pages, 2 figures

Beyond the Born rule in quantum gravity [CL]

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http://arxiv.org/abs/2212.12175


We have recently developed a new understanding of probability in quantum gravity. In this paper we provide an overview of this new approach and its implications. Adopting the de Broglie-Bohm pilot-wave formulation of quantum physics, we argue that there is no Born rule at the fundamental level of quantum gravity with a non-normalisable Wheeler-DeWitt wave functional $\Psi$. Instead the universe is in a perpetual state of quantum nonequilibrium with a probability density $P\neq\left\vert \Psi\right\vert ^{2}$. Dynamical relaxation to the Born rule can occur only after the early universe has emerged into a semiclassical or Schr\”{o}dinger approximation, with a time-dependent and normalisable wave functional $\psi$, for non-gravitational systems on a classical spacetime background. In that regime the probability density $\rho$ can relax towards $\left\vert \psi\right\vert ^{2}$ (on a coarse-grained level). Thus the pilot-wave theory of gravitation supports the hypothesis of primordial quantum nonequilibrium, with relaxation to the Born rule taking place soon after the big bang. We also show that quantum-gravitational corrections to the Schr\”{o}dinger approximation allow quantum nonequilibrium $\rho\neq\left\vert \psi\right\vert ^{2}$ to be created from a prior equilibrium ($\rho=\left\vert \psi\right\vert ^{2}$) state. Such effects are very tiny and difficult to observe in practice.

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A. Valentini
Mon, 26 Dec 22
12/39

Comments: 39 pages. For special issue of Foundations of Physics, ‘Pilot-wave and beyond: Louis de Broglie and David Bohm’s quest for a quantum ontology’, ed. A. Drezet

Dynamics of dark energy in a scalar-vector-torsion theory [CL]

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http://arxiv.org/abs/2212.12071


We study the cosmological dynamics of dark energy in a scalar-vector-torsion theory. The vector field is described by the cosmic triad and the scalar field is of the quintessence type with non-minimal coupling to gravity. The coupling to gravity is introduced through the interaction between the scalar field and torsion, where torsion is defined in the context of teleparallel gravity. We derive the full set of field equations for the Friedmann-Lema\^{i}tre-Robertson-Walker space-time background and obtain the associated autonomous system. We obtain the critical points and their stability conditions, along with the cosmological properties of them. Thus, we show that the thermal history of the universe is successfully reproduced. Furthermore, new scaling solutions in which the scalar and vector field densities scale in the same way as the radiation and matter background fluids have been found. Finally, we also show that there exist new attractor fixed points whose nature is mainly vectorial, and which can explain the current accelerated expansion and therefore the dark energy-domination.

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M. Gonzalez-Espinoza, G. Otalora, Y. Leyva, et. al.
Mon, 26 Dec 22
19/39

Comments: N/A

Some disquisitions on cosmological 2-form dualities [CL]

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http://arxiv.org/abs/2212.12427


In this work we study different aspect of self-interacting 2-form fields with special emphasis in their cosmological applications. We provide the explicit construction of how massless 2-forms are compatible with the cosmological principle without resorting to the dual scalar field formulation. In terms of the 2-form, the residual Euclidean group is non-trivially realised by means of a combination of external spatial translations and internal gauge transformations. After presenting the general discussion of the dualities in cosmological scenarios, we analyse particular examples for some singular models and discuss in some detail the dual descriptions of the DBI, the cuscuton and the ghost condensate as well as the role of the duality in the effective field theories of cosmological perturbations. We then proceed to analysing scenarios with several self-interacting massless 2-forms and we show that they naturally provide the dual description of a solid. We then show how the perfect fluid and superfluids can be obtained by taking the appropriate limits in the dual formulations. We finally consider the case of massive 2-forms and their duals and briefly discuss their potential signatures in gravitational waves astronomy.

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K. Aoki, J. Jiménez and D. Figueruelo
Mon, 26 Dec 22
29/39

Comments: 48 pages

Non-linear stability of $α'$-corrected Friedmann equations [CL]

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http://arxiv.org/abs/2212.11392


We study the non-linear stability of fixed-point solutions to the $\alpha’$-exact equations from O$(d,d)$ invariant cosmology, with and without matter perturbations. Previous non-linear analysis in the literature is revisited, and its compatibility with known linear perturbation results is shown. Some formal aspects of cosmological perturbations in duality invariant cosmology are discussed, and we show the existence of time-reparameterization invariant variables for perturbations.

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H. Bernardo, J. Chojnacki and V. Comeau
Fri, 23 Dec 22
27/58

Comments: 15 pages

Dark Matter and Baryogenesis from Visible-Sector Long-Lived Particles [CL]

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http://arxiv.org/abs/2212.11303


We present a minimal extension of the standard model that includes a long-lived fermion with weak-scale mass and an ${\cal O}({\rm GeV})$ fermionic dark matter candidate both of which are coupled to quarks. Decays of a TeV-scale colored scalar in a radiation-dominated phase bring the former to a thermal abundance while also producing dark matter. The long-lived fermion then dominates the energy density of the Universe and drives a period of early matter domination. It decays to reheat the Universe, mainly through baryon-number-violating interactions that also generate a baryon asymmetry, with a small branching fraction to dark matter. We find the allowed parameter space of the model and show that it can be probed by proposed long-lived particle searches as well as next-generation neutron-antineutron oscillation experiments. This model provides a robust explanation of dark matter and baryogenesis as long as the Universe is in a radiation-dominated phase at $T \gtrsim {\cal O}({\rm TeV})$.

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R. Allahverdi, J. Osiński and N. Loc
Fri, 23 Dec 22
34/58

Comments: 12 pages, 4 figures

Cosmological Double-Copy Relations [CL]

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http://arxiv.org/abs/2212.11282


We present differential double-copy relations between gluon and graviton three-point functions in (A)dS$_{d+1}$. We introduce a set of differential operators in (A)dS that naturally generalize on-shell kinematics of scattering amplitudes in flat space. This provides a way to construct (A)dS correlators by replacing the kinematic variables of amplitudes with the corresponding differential operators and suitably ordering them. By construction, the resulting correlators are manifestly conformally invariant, with the correct flat-space limit, and exhibit a differential double-copy structure.

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H. Lee and X. Wang
Fri, 23 Dec 22
39/58

Comments: 8 pages

Peaky Production of Light Dark Photon Dark Matter [CL]

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http://arxiv.org/abs/2212.11516


We explore a mechanism to produce a light dark photon dark matter through a coupling between the dark photon field and a spectator scalar field which plays no role in the inflationary expansion of the Universe while rolling down its potential during the inflation. The motion of the spectator field efficiently produces dark photons with large wavelengths which become non-relativistic before the time of matter-radiation equality. The spectrum of the wavelengths is peaky so that the constraint from the isocurvature perturbation can be evaded. The correct relic abundance is then achieved over a wide range of the dark photon mass down to $10^{-13} \ \text{eV}$. Our mechanism favors high-scale inflation models which can be tested in future observations. Furthermore, fluctuations of the dark photon field during inflation produce gravitational waves detectable at future space-based interferometers and/or pulsar timing array experiments.

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Y. Nakai, R. Namba and I. Obata
Fri, 23 Dec 22
54/58

Comments: 27 pages, 6 figures

Particles of a de Sitter Universe [CL]

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http://arxiv.org/abs/2212.10626


The de Sitter spacetime is a maximally symmetric spacetime. It is one of the vacuum solutions to Einstein equations with a cosmological constant. It is the solution with a positive cosmological constant and describes a universe undergoing accelerated expansion. Among the possible signs for a cosmological constant, this solution is relevant for primordial and late-time cosmology. In the case of zero cosmological constant, studies on the representations of its isometry group have led to a broader understanding of particle physics. The isometry group of $d+1$-dimensional de Sitter is the group $SO(d+1,1)$, whose representations are well known. Given this insight what can we learn about the elementary degrees of freedom in a four dimensional de Sitter universe by exploring how the unitary irreducible representations of $SO(4,1)$ present themselves in cosmological setups? This article aims to summarize recent advances along this line that benefit towards a broader understanding of quantum field theory and holography at different signs of the cosmological constant. Particular focus is given to the manifestation of $SO(4,1)$ representations at the late-time boundary of de Sitter. The discussion is concluded by pointing towards future questions at the late-time boundary and the static patch with a focus on the representations.

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G. Şengör
Thu, 22 Dec 22
17/59

Comments: Invited review for the special issue “Cosmological Constant” of journal Universe (ISSN 2218-1997). 37 pages

Thermalization, Fragmentation and Tidal Disruption: The Complex Galactic Dynamics of Dark Matter Superfluidity [CEA]

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http://arxiv.org/abs/2212.10577


The idea of self-interacting bosonic dark matter capable of exhibiting superfluidity is revisited. We show that the most interesting parameter space of the theory corresponds to fully thermalized dark matter halos. As a result the entire halo undergoes Bose-Einstein condensation due to high degeneracy. Since it is observationally preferable for the dark matter density profile to be similar to cold dark matter in the outskirts of the halo, we argue that the Jeans wavelength must be at least few times shorter than the virial radius. This entails that, upon condensation, a dark matter halo fragments into superfluid clumps. However, we demonstrate that these would-be solitons experience strong tidal disruption and behave as virialized weakly interacting streams. An exception is the central soliton, which can be as large as few tens of kiloparsecs in size without contradicting observational bounds. As a result, in dwarf galaxies, the observed rotation curves can be completely contained within the superfluid soliton. In this case, the dark matter distribution is expected to be strongly sensitive to the baryonic density profile. We argue that the diversity of rotation curves observed for dwarf galaxies is a natural consequence of the superfluid dark matter scenario.

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L. Berezhiani, G. Cintia and J. Khoury
Thu, 22 Dec 22
19/59

Comments: 28+1 pages, 4 figures

Reflections on Bubble Walls [CL]

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http://arxiv.org/abs/2212.10572


We discuss the dynamics of expanding bubble walls in the presence of massive dark photons whose mass changes as they cross the wall. For sufficiently thin walls, we show that there exists a transient kinematic regime characterized by a constant reflection probability of longitudinal — but not transverse — modes. This effect can have important implications for the dynamics of expanding vacuum bubbles in the early Universe. Most notably, it leads to a new source of pressure on the expanding interface, featuring a non-monotonic dependence on the $\gamma$-factor of the bubble walls and reaching a peak at intermediate $\gamma$-factors that we dub Maximum Dynamic Pressure. When this pressure is large enough to halt the acceleration of the bubble walls, the difference in vacuum energy densities goes into making a fraction of the dark photons relativistic, turning them into dark radiation. If the dark radiation remains relativistic until late times, an observable contribution to $\Delta N_\text{eff}$ is possible for phase transitions with strength $\alpha \sim 10^{-2} – 10^{-1}$.

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I. Garcia, G. Koszegi and R. Petrossian-Byrne
Thu, 22 Dec 22
33/59

Comments: 22 pages + appendices; 5 figures

Domain wall annihilation — a QFT perspective [CL]

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http://arxiv.org/abs/2212.11204


Domain wall networks in the early universe, formed upon spontaneous breaking of a discrete symmetry, have a rich impact on cosmology. Yet, they remain somewhat unexplored. We introduce a new analytic strategy to understand better the domain wall epoch, from formation to annihilation. Our method includes a quantum field theoretical treatment of the initial state at domain wall formation, as well as of the time evolution. We find that the domain wall area density for a network with biased initial condition in $d+1$ dimensional flat spacetime evolves as $t^{-1/2}\,\exp\big(- (t/t_{ann})^{d/2}\big)$. We comment on the relation between this and previous results obtained in condensed matter and in cosmology. The extrapolation of this law to an expanding universe applies to networks that are close to the domain wall `gas’ limit.

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O. Pujolas and G. Zahariade
Thu, 22 Dec 22
43/59

Comments: 14 pages, 5 figures

Generating enhanced parity-violating gravitational waves during inflation with violation of NEC [CL]

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http://arxiv.org/abs/2212.10893


A violation of the null energy condition (NEC) during inflation in a single field inflation model will naturally enhance the amplitude of the parity violation effect (defined by $\Delta\chi$) of inflationary primordial gravitational waves (GWs), provided the inflaton is non-minimally coupled to a gravitational Chern-Simons term. After going through the NEC-violating phase, the universe enters subsequent slow-roll inflation with a higher scale, which results in an enhanced nearly scale-invariant power spectrum (i.e., $P_{\rm T}$) of inflationary primordial GWs in the high-frequency band, while $P_{\rm T}$ remains consistent with observations in the frequency band of the cosmic microwave background. Therefore, the violation of NEC during inflation will amplify the observability (i.e., $P_{\rm T}\cdot\Delta\chi$) of the parity violation effect. For a sufficiently large $P_{\rm T}$, a $\Delta\chi$ as small as a few percent can imprint a significant signal of parity violation in the GWs background, which might be detectable for pulsar timing arrays and space-based detectors in the future.

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Y. Cai
Thu, 22 Dec 22
53/59

Comments: 19 pages, 16 figures

A systematic formulation of chiral anomalous magnetohydrodynamics [CL]

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http://arxiv.org/abs/2212.09757


We present a new way of deriving effective theories of dynamical electromagnetic fields in general media. It can be used to give a systematic formulation of magnetohydrodynamics (MHD) with strong magnetic fields, including systems with chiral matter and Adler-Bell-Jackiw (ABJ) anomaly. We work in the regime in which velocity and temperature fluctuations can be neglected. The resulting chiral anomalous MHD incorporates and generalizes the chiral magnetic effect, the chiral separation effect, the chiral electric separation effect, as well as recently derived strong-field MHD, all in a single coherent framework. At linearized level, the theory predicts that the chiral magnetic wave survives strong dynamical magnetic fields, and predicts the wave velocity. We also introduce a simple, but solvable nonlinear model to explore the fate of the chiral instability.

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M. Landry and H. Liu
Wed, 21 Dec 22
3/81

Comments: 22 pages

Glimpse of Quantum Gravitons post the Last Scattering Surface [CL]

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http://arxiv.org/abs/2212.09784


In the cosmological settings, Quantum Gravity effects are typically understood to be limited towards very early phase of the universe, namely in the pre-inflationary era, with limited signatures remaining present in the succeeding inflationary era. These signatures also gradually fade away as the universe grows and exits the inflationary era. In the subsequent radiation and matter dominated era quantum gravity is expected to play no significant role. Classicalized primordial perturbations such as the scalar perturbations and the gravitational waves are expected to leave an imprint on CMB anisotropy and its polarization respectively but quantized gravitational waves are not expected to lead to any appreciable observable effects. Apart from cosmology, in other avenues as well, the imprints of quantum character of gravitational waves are typically so subdued that any possible signature gets buried under a huge pile of the noise or effects from other much stronger processes. In this work, we demonstrate that quantum gravity perturbations cause strong observable effects in cosmological settings post the Last Scattering Surface (LSS) more prominently than any other classical or quantum processes. This counter-intuitive effect is facilitated by the fact that the correlators of the gravitational waves {\it grow divergently large in the matter dominated era} unlike any other background fields, leading to an abrupt rise in the processes mediated by correlators of quantum gravitons. The transitions between spherical harmonics states of newly formed hydrogen atom at the LSS, when the universe resides in strong matter dominated era, provides an example of such a process. We further establish that the late time epoch just before the kicking in of the dark energy provides one of the cleanest avenues to study such quantum gravity effects.

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A. Dhanuka and K. Lochan
Wed, 21 Dec 22
6/81

Comments: 12 pages, 1 Figure

The hypermagnetic power spectra and the phases of Sakharov oscillations [CL]

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http://arxiv.org/abs/2212.10214


If the gauge fields are amplified from the inflationary vacuum, the quantum mechanical initial data correspond to travelling waves that turn asymptotically into standing waves whose phases only depend on the evolution of the gauge coupling. We point out that these gauge analogs of the Sakharov oscillations are exchanged by the duality symmetry and ultimately constrain both the relative scaling of the hypermagnetic power spectra and their final asymptotic values. Unlike the case of the density contrasts in a relativistic plasma, the standing oscillations never develop since they are eventually overdamped by the finite value of the conductivity as soon as the corresponding modes are comparable with the expansion rates after inflation. We show that the late-time value of the magnetic field is not determined at radiation dominance (and in spite of the value of the wavenumber) but it depends on the moment when the wavelengths (comparable with the Mpc) get of the order of the Hubble radius before equality. This means that the magnetogenesis requirements are only relaxed if the post-inflationary expansion rate is slower than radiation but the opposite is true when the plasma expands faster than radiation and the corresponding power spectra are further suppressed. After combining the present findings with the evolution of the gauge coupling we show that these results are consistent with a magnetogenesis scenario where the gauge coupling is always perturbative during the inflationary stage while, in the dual case, the same requirements cannot be satisfied.

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M. Giovannini
Wed, 21 Dec 22
11/81

Comments: 40 pages, 11 figures

A novel test of gravity via black hole eikonal correspondence [CL]

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http://arxiv.org/abs/2212.10028


When adopted in black hole spacetimes, geometric-optics approximations imply a mapping between the quasinormal mode (QNM) spectrum of black holes in the eikonal limit and black hole images. In particular, the real part and the imaginary part of eikonal QNM frequencies are associated with the apparent size and the detailed structure of the ring images, respectively. This correspondence could be violated when going beyond general relativity. We propose a novel method to test the eikonal correspondence via the comparison of two sets of observables from a nonrotating black hole, one extracted from QNM spectra and the other from the lensed photon rings on the image plane. Specifically, the photon ring observables robustly capture the information of the black hole spacetime itself regardless of the surrounding emission models. Therefore, the proposed test of eikonal correspondence can be validated in quite broad scenarios.

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C. Chen, Y. Chen, M. Ho, et. al.
Wed, 21 Dec 22
22/81

Comments: 8 pages, 2 figures

Cosmological stability in $f(φ,{\cal G})$ gravity [CL]

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http://arxiv.org/abs/2212.10022


In gravitational theories where a canonical scalar field $\phi$ with a potential $V(\phi)$ is coupled to a Gauss-Bonnet (GB) term ${\cal G}$ with the Lagrangian $f(\phi,{\cal G})$, we study the cosmological stability of tensor and scalar perturbations in the presence of a perfect fluid. We show that, in decelerating cosmological epochs with a positive tensor propagation speed squared, the existence of nonlinear functions of ${\cal G}$ in $f$ always induces Laplacian instability of a dynamical scalar perturbation associated with the GB term. This is also the case for $f({\cal G})$ gravity, where the presence of nonlinear GB functions $f({\cal G})$ is not allowed during the radiation- and matter-dominated epochs. A linearly coupled GB term with $\phi$ of the form $\xi (\phi){\cal G}$ can be consistent with all the stability conditions, provided that the scalar-GB coupling is subdominant to the background cosmological dynamics.

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S. Tsujikawa
Wed, 21 Dec 22
25/81

Comments: 13 pages, no figures

A new universal property of cosmological gravitational wave anisotropies [CL]

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http://arxiv.org/abs/2212.10316


The anisotropies of the stochastic gravitational wave background, as produced in the early phases of cosmological evolution, can act as a key probe of the primordial universe particle content. We point out a new universal property of gravitational wave anisotropies of cosmological origin: for adiabatic initial conditions, their angular power spectrum is insensitive to the equation of state of the cosmic fluid driving the expansion before big-bang nucleosynthesis. Any deviation from this universal behaviour points to the presence of non-adiabatic sources of primordial fluctuations. Such scenarios can be tested by gravitational wave detectors operating at a frequency range which is fully complementary to CMB experiments. In this work we prove this general result, and we illustrate its consequences for a representative realisation of initial conditions based on the curvaton scenario. In the case of the simplest curvaton setup, we also find a significant cross-correlation between gravitational wave anisotropies and the CMB temperature fluctuations. There is a fourfold enhancement vis-`{a}-vis the purely adiabatic scenario. We discuss the implications of our findings for identifying the origin of the (cosmological) gravitational wave background when, as is often the case, this cannot be determined solely on the basis of its spectral shape.

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A. Malhotra, E. Dimastrogiovanni, G. Domènech, et. al.
Wed, 21 Dec 22
31/81

Comments: 14 pages, 4 figures

Quasar UV/X-ray relation luminosity distances are shorter than reverberation-measured radius-luminosity relation luminosity distances [CEA]

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http://arxiv.org/abs/2212.10483


We use measurements of 59/58 quasars (QSOs), over a redshift range $0.0041\leq z \leq 1.686$, to do a comparative study of the radius–luminosity ($R-L$) and X-ray$-$UV luminosity ($L_X-L_{UV}$) relations and the implication of these relations for cosmological parameter estimation. By simultaneously determining $R-L$ or $L_X-L_{UV}$ relation parameters and cosmological parameters in six different cosmological models, we find that both $R-L$ and $L_X-L_{UV}$ relations are standardizable but provide only weak cosmological parameter constraints, with $L_X-L_{UV}$ relation data favoring larger current non-relativistic matter density parameter $\Omega_{m0}$ values than $R-L$ relation data and most other available data. We derive $L_X-L_{UV}$ and $R-L$ luminosity distances for each of the sources in the six cosmological models and find that $L_X-L_{UV}$ relation luminosity distances are shorter than $R-L$ relation luminosity distances as well as standard flat $\Lambda$CDM model luminosity distances. This explains why $L_X-L_{UV}$ relation QSO data favor larger $\Omega_{m0}$ values than do $R-L$ relation QSO data or most other cosmological measurements. While our sample size is small and only spans a small $z$ range, these results indicate that more work is needed to determine whether the $L_X-L_{UV}$ relation can be used as a cosmological probe.

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N. Khadka, M. Zajaček, R. Prince, et. al.
Wed, 21 Dec 22
32/81

Comments: 19 pages, 9 figures

Renormalizing one-point probability distribution function for cosmological counts in cells [CEA]

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http://arxiv.org/abs/2212.09799


We study the one-point probability distribution function (PDF) for matter density averaged over spherical cells. The leading part to the PDF is defined by the dynamics of the spherical collapse whereas the next-to-leading part comes from the integration over fluctuations around the saddle-point solution. The latter calculation receives sizable contributions from unphysical short modes and must be renormalized. We propose a new approach to renormalization by modeling the effective stress-energy tensor for short perturbations. The model contains three free parameters related to the counterterms in the one-loop matter power spectrum and bispectrum, as well as their redshift dependence. This relation can be used to impose priors in fitting the model to the PDF data. We confront the model with the results of high-resolution N-body simulations and find excellent agreement for cell radii $r_\geq 10\,{\rm Mpc}/h$ at all redshifts up to $z=0$. Discrepancies at a few per cent level are detected at low redshifts for $r_\leq 10\,{\rm Mpc}/h$ and are associated with two-loop corrections to the model.

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A. Chudaykin, M. Ivanov and S. Sibiryakov
Wed, 21 Dec 22
36/81

Comments: 70 pages, 18 figures, 3 tables

Thermal Production of Massless Dark Photons [CL]

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http://arxiv.org/abs/2212.09755


A dark photon is predicted by several well-motivated Standard Model extensions and UV completions. Here the most general effective field theory up to dimension-six operators describing the interactions of a massless dark photon with all Standard Model particles is considered. This captures the predictions of a generic model featuring this type of vector boson at sufficiently low energies. In such framework the thermal production rate of dark photons is computed at leading order, including the contributions of all SM particles. The corresponding cosmological yield of the dark photon and its contribution to the effective number of neutrinos are also calculated. These predictions satisfy the current observational bounds and will be tested by future measurements.

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A. Salvio
Wed, 21 Dec 22
39/81

Comments: 16 pages, 4 figures

Inflation in Metric-Affine Quadratic Gravity [CL]

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http://arxiv.org/abs/2212.09896


In the general framework of Metric-Affine theories of gravity, where the metric and the connection are independent variables, we consider actions quadratic in the Ricci scalar curvature and the Holst invariant (the contraction of the Riemann curvature with the Levi-Civita antisymmetric tensor) coupled non-minimally to a scalar field. We study the profile of the equivalent effective metric theory, featuring an extra dynamical pseudoscalar degree of freedom, and show that it reduces to an effective single-field inflationary model. We analyze in detail the inflationary predictions and find that they fall within the latest observational bounds for a wide range of parameters, allowing for an increase in the tensor-to-scalar ratio. The spectral index can either decrease or increase depending on the position in parameter space.

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I. Gialamas and K. Tamvakis
Wed, 21 Dec 22
53/81

Comments: 21 pages, 7 figures, 3 tables

Towards an effective action for chiral magnetohydrodynamics [CL]

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http://arxiv.org/abs/2212.09787


We consider chiral magnetohydrodynamics, i.e. a finite-temperature system where an axial $U(1)$ current is not conserved due to an Adler-Bell-Jackiw anomaly saturated by the dynamical operator $F_{\mu\nu} \tilde{F}^{\mu\nu}$. We express this anomaly in terms of the 1-form symmetry associated with magnetic flux conservation and study its realization at finite temperature. We present Euclidean generating functional and dissipative action approaches to the dynamics and reproduce some aspects of chiral MHD phenomenology from an effective theory viewpoint, including the chiral separation and magnetic effects. We also discuss the construction of non-invertible axial symmetry defect operators in our formalism.

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A. Das, N. Iqbal and N. Poovuttikul
Wed, 21 Dec 22
73/81

Comments: revtex, 29+6 pages

Leptogenesis via Inflaton Mass Terms in Non-Minimally Coupled Inflation [CL]

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http://arxiv.org/abs/2212.09454


We consider a model of baryogenesis based on adding lepton number-violating quadratic mass terms to the inflaton potential of a non-minimally coupled inflation model. The $L$-violating mass terms generate a lepton asymmetry in a complex inflaton field via the mass term Affleck-Dine mechanism, which is transferred to the Standard Model (SM) sector when the inflaton decays to right-handed (RH) neutrinos. The model is minimal in that it requires only the SM sector, RH neutrinos, and a non-minimally coupled inflaton sector. We find that baryon isocurvature fluctuations can be observable in metric inflation but are negligible in Palatini inflation. The model is compatible with reheating temperatures that may be detectable in the observable primordial gravitational waves predicted by metric inflation.

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K. Lloyd-Stubbs and J. McDonald
Tue, 20 Dec 22
30/97

Comments: 18 pages, 6 figures

Gravity, Horizons and Open EFTs [CL]

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http://arxiv.org/abs/2212.09157


Wilsonian effective theories exploit hierarchies of scale to simplify the description of low-energy behaviour and play as central a role for gravity as for the rest of physics. They are useful both when hierarchies of scale are explicit in a gravitating system and more generally for understanding precisely what controls the size of quantum corrections in gravitational systems. But effective descriptions are also relevant for open systems (e.g. fluid mechanics as a long-distance description of statistical systems) for which the `integrating out’ of unobserved low-energy degrees of freedom complicate a straightforward application of Wilsonian methods. Observations performed only on one side of an apparent horizon provide examples where open system descriptions also arise in gravitational physics. This chapter describes some early adaptations of Open Effective Theories (i.e. techniques for exploiting hierarchies of scale in open systems) in gravitational settings. Besides allowing the description of new types of phenomena (such as decoherence) these techniques also have an additional benefit: they sometimes can be used to resum perturbative expansions at late times and thereby to obtain controlled predictions in a regime where perturbative predictions otherwise generically fail.

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C. Burgess and G. Kaplanek
Tue, 20 Dec 22
50/97

Comments: 52 pages, 5 Figures; Invited chapter for the Section “Effective Quantum Gravity” edited by C. Burgess and J. Donoghue of the “Handbook of Quantum Gravity” (Eds. C. Bambi, L. Modesto and I.L. Shapiro, Springer Singapore, expected in 2023)

Quantum recoherence in the early universe [CL]

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http://arxiv.org/abs/2212.09486


Despite being created through a fundamentally quantum-mechanical process, cosmological structures have not yet revealed any sign of genuine quantum correlations. Among the obstructions to the direct detection of quantum signatures in cosmology, environmental-induced decoherence is arguably one of the most inevitable. Yet, we discover a mechanism of quantum recoherence for the adiabatic perturbations when they couple to an entropic sector. After a transient phase of decoherence, a turning point is reached, recoherence proceeds and adiabatic perturbations exhibit a large amount of self-coherence at late-time. This result is also understood by means of a non-Markovian master equation, which reduces to Wilsonian effective-field theory in the unitary limit. This allows us to critically assess the validity of open-quantum-system methods in cosmology and to highlight that re(de)coherence from linear interactions has no flat-space analogue.

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T. Colas, J. Grain and V. Vennin
Tue, 20 Dec 22
59/97

Comments: 5 + 12 pages, 4 + 2 figures

TASI Lectures on Cosmic Signals of Fundamental Physics [CL]

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http://arxiv.org/abs/2212.08685


The history of the Universe and the forces that shaped it are encoded in maps of the cosmos. From understanding these maps, we gain insights into nature that are inaccessible by other means. Unfortunately, the connection between fundamental physics and cosmic observables is often left to experts (and/or computers), making the general lessons from data obscure to many particle theorists. Fortunately, the same basic principles that govern the interactions of particles, like locality and causality, also control the evolution of the Universe as a whole and the manifestation of new physics in data. By focusing on these principles, we can understand more intuitively how the next generation of cosmic surveys will inform our understanding of fundamental physics. In these lectures, we will explore this relationship between theory and data through three examples: light relics ($N_{\rm eff}$) and the cosmic microwave background (CMB), neutrino mass and gravitational lensing of the CMB, and primordial non-Gaussianity and the distribution of galaxies. We will discuss both the theoretical underpinnings of these signals and the real-world obstacles to making the measurements.

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D. Green
Tue, 20 Dec 22
62/97

Comments: 72 pages, 14 figures, 2 tables

A Dark Matter Trigger for Early Dark Energy Coincidence [CEA]

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http://arxiv.org/abs/2212.08098


Early dark energy (EDE), whose cosmological role is localized in time around the epoch of matter-radiation equality in order to resolve the Hubble tension, introduces a new coincidence problem: why should the EDE dynamics occur near equality if EDE is decoupled from both matter and radiation? The resolution of this problem may lie in an {\it early dark sector} (EDS), wherein the dark matter mass is dependent on the EDE scalar field. Concretely, we consider a Planck-suppressed coupling of EDE to dark matter, as would naturally arise from breaking of the global $U(1)$ shift symmetry of the former by quantum gravity effects. With a sufficiently flat potential, the rise to dominance of dark matter at matter-radiation equality itself triggers the rolling and subsequent decay of the EDE. We show that this {\it trigger} EDS (tEDS) model can naturally resolve the EDE coincidence problem at the background level without any fine tuning of the coupling to dark matter or of the initial conditions. When fitting to current cosmological data, including that from the local distance ladder and the low-redshift amplitude of fluctuations, the tEDS maximum-likelihood model performs comparably to EDE for resolving the Hubble tension, achieving $H_0 =71.2$ km/s/Mpc. However, fitting the \emph{Planck} cosmic microwave background data requires a specific range of initial field positions to balance the scalar field fluctuations that drive acoustic oscillations, providing testable differences with other EDE models.

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M. Lin, E. McDonough, J. Hill, et. al.
Mon, 19 Dec 22
7/62

Comments: 12 pages, 6 figures

Microcanonical Hamiltonian Monte Carlo [CL]

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http://arxiv.org/abs/2212.08549


We develop Microcanonical Hamiltonian Monte Carlo (MCHMC), a class of models which follow a fixed energy Hamiltonian dynamics, in contrast to Hamiltonian Monte Carlo (HMC), which follows canonical distribution with different energy levels. MCHMC tunes the Hamiltonian function such that the marginal of the uniform distribution on the constant-energy-surface over the momentum variables gives the desired target distribution. We show that MCHMC requires occasional energy conserving billiard-like momentum bounces for ergodicity, analogous to momentum resampling in HMC. We generalize the concept of bounces to a continuous version with partial direction preserving bounces at every step, which gives an energy conserving underdamped Langevin-like dynamics with non-Gaussian noise (MCLMC). MCHMC and MCLMC exhibit favorable scalings with condition number and dimensionality. We develop an efficient hyperparameter tuning scheme that achieves high performance and consistently outperforms NUTS HMC on several standard benchmark problems, in some cases by more than an order of magnitude.

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J. Robnik, G. Luca, E. Silverstein, et. al.
Mon, 19 Dec 22
28/62

Comments: 32 pages, 10 figures

Effective Field Theory for Large Scale Structure [CEA]

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http://arxiv.org/abs/2212.08488


This chapter is a non-expert introduction to the effective field theory of large scale structure. First, we give a detailed pedagogical explanation of why previous attempts to build non-linear cosmological perturbation theory failed. After that we introduce the description of dark matter as an effective non-ideal fluid and show how it corrects the shortcomings of the previous approaches. Finally, we develop a formulation of the effective field theory of large-scale structure from a nonequilibrium field theory perspective, called time-sliced perturbation theory. We show how this framework can be used for a consistent renormalization of cosmological correlation functions and a systematic resummation of large infrared effects relevant for the baryon acoustic oscillations.

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M. Ivanov
Mon, 19 Dec 22
35/62

Comments: 46 pages, 11 figures. Invited chapter for the Section “Effective Quantum Gravity” edited by C. Burgess and J. Donoghue of the “Handbook of Quantum Gravity” (Eds. C. Bambi, L. Modesto and I.L. Shapiro, Springer Nature, expected in 2023)

Aspects of the Dark Dimension in Cosmology [CL]

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http://arxiv.org/abs/2212.08527


It was recently understood that if the swampland conjectures are confronted to experiment they naturally point to a solution of the cosmological hierarchy problem in which the smallness of the dark energy is ascribed to an internal (dark) dimension with characteristic length-scale in the micron range. It was later inferred that the universal coupling of the Standard Model fields to the massive spin-2 Kaluza-Klein (KK) excitations of the graviton in the dark dimension gives an unavoidable dark matter candidate. Since the partial decay widths of KK gravitons into the visible sector must be relatively small to accommodate experiment, the model is particularly challenging to probe. We study the impact of the KK tower in cosmology. We show that the modulation of redshifted 21-cm lines driven by ${\rm KK} \to \gamma \gamma$ is within the reach of next generation experiments (e.g. SKA and FARSIDE). We also explore the global structure of the inflationary phase and show that the model parameters required for a successful uniform inflation driven by a 5-dimensional cosmological constant (corresponding to a flat region of the 5-dimensional potential) are natural.

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L. Anchordoqui, I. Antoniadis and D. Lust
Mon, 19 Dec 22
44/62

Comments: 14 pages revtex with 1 figure

The scaling of primordial gauge fields [CEA]

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http://arxiv.org/abs/2212.07929


It has been conjectured that a specific set of Cauchy data may lead to an unexpected growth of the gauge fields in conformally flat cosmological backgrounds. After introducing a class of models where the (hyper)magnetic fields are produced quantum mechanically from the early variation of the gauge coupling, we show that the standard evolution for wavelengths larger than the Hubble radius fully accounts for the anomalous scaling which is however unable to increase the magnetic power spectra. This dynamical evolution has nothing to do with a peculiar choice of the initial conditions but rather with the rate of variation of the gauge coupling during inflation. While the correct scaling follows from the properly normalized solutions of the mode functions and from the late dominance of the conductivity, a further amplification of the magnetic power spectra can only occur when the post-inflationary expansion rate is slower than radiation and it is again unrelated to the initial data possibly set during the inflationary stage.

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M. Giovannini
Fri, 16 Dec 22
11/72

Comments: 10 pages, 1 figure

Mass-varying Dark Matter from a Phase Transition [CL]

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http://arxiv.org/abs/2212.07884


We propose a mass-varying dark matter (MVDM) model consisting of a scalar field and a fermionic field interacting via a simple Yukawa coupling, and containing an exponential self-interaction potential for the scalar field. Analyzing the evolution of this coupled scalar-fermion system in an expanding Universe, we find that it initially behaves like radiation but then undergoes a phase transition after which it behaves like pressureless dark matter. The two free parameters of this model are the temperature at which the phase transition occurs and the current relic density of dark matter; the mass of the dark matter particle, given by the mass of the fermion, is derived from this. For a phase transition temperature between 10 MeV and $10^7$ GeV, the current dark matter relic density is achieved for a fermion mass in the range of 1 GeV to $10^9$ GeV. In this dark matter model, the scalar becomes a sub-dominant unclustered component of dark matter that can lower the amplitude of structure formation by up to a few percent. Another feature is that the mass-varying fermion component can lead to discrepant measurements of the current dark matter density of about ten percent inferred from early and late-time probes assuming LCDM.

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S. Mandal and N. Sehgal
Fri, 16 Dec 22
12/72

Comments: 11 pages, 7 figures; Mathematica code and notes for numerical/analytic calculations are provided at this https URL

Towards A Direct Detection of the Spin of Dark Matter [CL]

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http://arxiv.org/abs/2212.07442


We investigate the contribution of higher spin particles in the signal of direct detection experiments searching for dark matter. We consider a bosonic or fermionic higher spin dark matter (HSDM) candidate which interacts with the Standard Model via a dark U(1) mediator. For a particular subclass of interactions, spin-polarized targets may be used for spin determination: The angular dependence of scatterings can distinguish integer (spin-$s$) vs. half-integer (spin-$s + 1/2$), while the recoil energy dependence of the signal determines $s$. We consider also the signal of a supersymmetric higher spin dark sector, which suggests a characteristic signal (”SUSY Rilles”) for directional direct detection.

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L. Jenks, K. Koutrolikos, E. McDonough, et. al.
Fri, 16 Dec 22
15/72

Comments: 22 pages, 6 figures

Erasure of Strings and Vortexes [CL]

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http://arxiv.org/abs/2212.07535


The interaction of defects can lead to a phenomenon of erasure. During this process, a lower-dimensional object gets absorbed and dissolved by a higher-dimensional one. The phenomenon is very general and has a wide range of implications, both cosmological and fundamental. In particular, all types of strings, such as cosmic strings, QCD flux tubes, or fundamental strings, get erased when encountering a defect, either solitonic or a $D$-brane that deconfines their fluxes. This leads to a novel mechanism of cosmic string break-up, accompanied by gravitational and electromagnetic radiations. The arguments based on loss of coherence and the entropy count suggest that the erasure probability is very close to one, and strings never make it through the deconfining layer. We confirm this by a numerical simulation of the system, which effectively captures the essence of the phenomenon: a $2+1$-dimensional problem of interaction between a Nielsen-Olesen vortex of a $U(1)$ Higgs model and a domain wall inside which the $U(1)$ gauge group is unHiggsed and the magnetic flux is deconfined. In accordance with the entropy argument, in our simulation, the vortex never makes it across the wall.

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G. Dvali and J. Valbuena-Bermúdez
Fri, 16 Dec 22
20/72

Comments: 11 pages, 7 figures, the results of our numerical simulations can be visualized in the following \href{this https URL}{video}

A New Test of Dynamical Dark Energy Models and Cosmic Tensions in Hořava Gravity [CEA]

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http://arxiv.org/abs/2212.07683


Horava gravity has been proposed as a renormalizable, higher-derivative, Lorentz-violating quantum gravity model without ghost problems. A Horava gravity based dark energy (HDE) model for dynamical dark energy has been also proposed earlier by identifying all the extra (gravitational) contributions from the Lorentz-violating terms as an effective energy-momentum tensor in Einstein equation. We consider a complete CMB, BAO, and SNe Ia data test of the HDE model by considering general perturbations over the background perfect HDE fluid. Except from BAO, we obtain the preference of non-flat universes for all other data-set combinations. We obtain a positive result on the cosmic tensions between the Hubble constant H0 and the cosmic shear S8, because we have a shift of H0 towards a higher value, though not enough for resolving the H0 tension, but the value of S8 is unaltered. This is in contrast to a rather decreasing H0 but increasing S8 in a non-flat LCDM. For all other parameters, like Omega_m and Omega_Lambda, we obtain quite comparable results with those of LCDM for all data sets, especially with BAO, so that our results are close to a cosmic concordance between the datasets, contrary to the standard non-flat LCDM. We also obtain some undesirable features but we propose several promising ways for improvements by generalizing our analysis.

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E. Valentino, N. Nilsson and M. Park
Fri, 16 Dec 22
35/72

Comments: 21 pages, 10 figures

Spontaneous Scalarization of Black Holes in Gauss-Bonnet Teleparallel Gravity [CL]

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http://arxiv.org/abs/2212.07653


In this paper, we find new scalarized black holes by coupling a scalar field with the Gauss-Bonnet invariant in Teleparallel gravity. The Teleparallel formulation of this theory uses torsion instead of curvature to describe the gravitational interaction and it turns out that, in this language, the usual Gauss-Bonnet term in four dimensions, decays in two distinct boundary terms, the Teleparallel Gauss-Bonnet invariants. Both can be coupled individually, or in any combination, to a scalar field, to obtain a Teleparallel Gauss-Bonnet extension of the Teleparallel equivalent of general relativity. The theory we study contains the familiar Riemannian Einstein-Gauss-Bonnet gravity theory as a particular limit and offers a natural extension, in which scalarization is triggered by torsion and with new interesting phenomenology. We demonstrate numerically the existence of asymptotically flat scalarized black hole solutions and show that, depending on the choice of coupling of the boundary terms, they can have a distinct behaviour compared to the ones known from the usual Einstein-Gauss-Bonnet case. More specifically, non-monotonicity of the metric functions and the scalar field can be present, a feature that was not observed until now for static scalarized black hole solutions.

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S. Bahamonde, D. Doneva, L. Ducobu, et. al.
Fri, 16 Dec 22
50/72

Comments: 21 pages, 10 figures

Finite energy sum rules for gravitational Regge amplitudes [CL]

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http://arxiv.org/abs/2212.08001


We develop a framework to derive consistency constraints on gravitational Regge amplitudes based on the finite energy sum rules (FESRs), which directly connect gravitational Regge amplitudes at a finite ultraviolet scale with infrared physics without suffering from super-Planckian physics. For illustration, we consider four-point scattering of an identical massless scalar coupled to gravity. First, we derive multiple FESRs without relying on the $s\text{-}t\text{-}u$ permutation invariance. We then make use of FESRs, crossing symmetry, and other principles such as unitarity, to derive bounds on the Regge parameters. The bounds result in infrared finite gravitational positivity bounds in four spacetime dimensions.

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T. Noumi and J. Tokuda
Fri, 16 Dec 22
54/72

Comments: 22 pages plus appendices, 11 figures

Symmetric Teleparallel Horndeski [CL]

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http://arxiv.org/abs/2212.08005


Horndeski gravity is the most general scalar-tensor theory with one scalar field leading to second-order Euler-Lagrange field equations for the metric and scalar field, and it is based on Riemannian geometry. In this paper, we formulate an analogue version of Horndeski gravity in a symmetric teleparallel geometry which assumes that both the curvature (general) and torsion are vanishing and gravity is only related to nonmetricity. Our setup requires that the Euler-Lagrange equations for not only metric and scalar field but also connection should be at most second order. We find that the theory can be always recast as a sum of the Riemannian Horndeski theory and new terms that are purely teleparallel. Due to the nature of nonmetricity, there are many more possible ways of constructing second-order theories of gravity. In this regard, up to some assumptions, we find the most general $k$-essence extension of Symmetric Teleparallel Horndeski. We also formulate a novel theory containing higher-order derivatives acting on nonmetricity while still respecting the second-order conditions, which can be recast as an extension of Kinetic Gravity Braiding. We finish our study by presenting the FLRW cosmological equations for our model.

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S. Bahamonde, G. Trenkler, L. Trombetta, et. al.
Fri, 16 Dec 22
58/72

Comments: 34 pages

Searching for Domain Wall Network by Parkes Pulsar Timing Array [CL]

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http://arxiv.org/abs/2212.07871


We search for stochastic gravitational wave background generated by domain wall networks in the Data Release-2 of Parkes Pulsar Timing Array and find that the observed strong common power-law process can be explained by domain wall networks for the wall tension $\sigma_{\rm{DW}}\sim (29-414~\rm{TeV})^3$ and the wall-decay temperature $T_d\sim 26-363~\rm{MeV}$. Interestingly, the same parameter region can largely alleviate the Hubble tension, if the free particles generated from domain wall networks further decay into dark radiation. In addition, the preferred parameter space corresponds to the axion mass range $m_a \sim 10^{-13}-10^{-8}\ {\rm eV}$ for QCD axion. On the other hand, assuming that the common power-law process is not due to domain wall networks, we can put stringent constraints on the wall tension and decay temperature around the energy scale of QCD phase transition.

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L. Bian, S. Ge, C. Li, et. al.
Fri, 16 Dec 22
59/72

Comments: 18 pages, 13 figures, 4 tables. Comments welcome

The graviton four-point function in de Sitter space [CL]

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http://arxiv.org/abs/2212.07370


We compute the tree-level late-time graviton four-point correlation function, and the related quartic wavefunction coefficient, for Einstein gravity in de Sitter spacetime. We derive this result in several ways: by direct calculation, using the in-in formalism and the wavefunction of the universe; by a heuristic derivation leveraging the flat space wavefunction coefficient; and by using the boostless cosmological bootstrap, in particular the combination of the cosmological optical theorem, the amplitude limit, and the manifestly local test. We find agreement among the different methods.

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J. Bonifacio, H. Goodhew, A. Joyce, et. al.
Thu, 15 Dec 22
3/75

Comments: 46 pages

Efficiently evaluating loop integrals in the EFTofLSS using QFT integrals with massive propagators [CEA]

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http://arxiv.org/abs/2212.07421


We develop a new way to analytically calculate loop integrals in the Effective Field Theory of Large Scale-Structure. Previous available methods show severe limitations beyond the one-loop power spectrum due to analytical challenges and computational and memory costs. Our new method is based on fitting the linear power spectrum with cosmology-independent functions that resemble integer powers of quantum field theory massive propagators with complex masses. A remarkable small number of them is sufficient to reach enough accuracy. Similarly to former approaches, the cosmology dependence is encoded in the coordinate vector of the expansion of the linear power spectrum in our basis. We first produce cosmology-independent tensors where each entry is the loop integral evaluated on a given combination of basis vectors. For each cosmology, the evaluation of a loop integral amounts to contracting this tensor with the coordinate vector of the linear power spectrum. The 3-dimensional loop integrals for our basis functions can be evaluated using techniques familiar to particle physics, such as recursion relations and Feynman parametrization. We apply our formalism to evaluate the one-loop bispectrum of galaxies in redshift space. The final analytical expressions are quite simple and can be evaluated with little computational and memory cost. We show that the same expressions resolve the integration of all one-loop $N$-point function in the EFTofLSS. This method, which is originally presented here, has already been applied in the first one-loop bispectrum analysis of the BOSS data to constraint $\Lambda$CDM parameters and primordial non-Gaussianities, see arXiv:2206.08327 and arXiv:2201.11518.

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C. Anastasiou, D. Bragança, L. Senatore, et. al.
Thu, 15 Dec 22
24/75

Comments: 69 + 27 pages, 27 figures. arXiv admin note: text overlap with arXiv:2111.05739 by other authors

Quantum Tunneling of Ultralight Dark Matter Out of Satellite Galaxies [CEA]

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http://arxiv.org/abs/2212.07386


The idea of ultralight scalar (axion) dark matter is theoretically appealing and may resolve some small-scale problems of cold dark matter; so it deserves careful attention. In this work we carefully analyze tunneling of the scalar field in dwarf satellites due to the tidal gravitational force from the host halo. The tidal force is far from spherically symmetric; causing tunneling along the axis from the halo center to the dwarf, while confining in the orthogonal plane. We decompose the wave function into a spherical term plus higher harmonics, integrate out angles, and then numerically solve a residual radial Schr\”odinger-Poisson system. By demanding that the core of the Fornax dwarf halo can survive for at least the age of the universe places a bound on the dark matter particle mass $2\times 10^{-22}\,\mbox{eV}\lesssim m\lesssim 6\times 10^{-22}\,$eV. Interestingly, we show that if another very low density halo is seen, then it rules out the ultralight scalar as core proposal completely. Furthermore, the non-condensed particles likely impose an even sharper lower bound. We also determine how the residual satellites could be distributed as a function of radius.

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M. Hertzberg and A. Loeb
Thu, 15 Dec 22
68/75

Comments: 6 pages, 2 figures, in double column format

A new approach and code for spinning black holes in modified gravity [CL]

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http://arxiv.org/abs/2212.07293


We discuss and implement a spectral method approach to computing stationary and axisymmetric black hole solutions and their properties in modified theories of gravity. The resulting code is written in the Julia language and is transparent and easily adapted to new settings. We test the code on both general relativity and on Einstein-Scalar-Gauss-Bonnet gravity. It is accurate and fast, converging on a spinning solution in these theories with tiny errors ($\sim \mathcal{O}\left(10^{-13}\right)$ in most cases) in a matter of seconds.

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P. Fernandes and D. Mulryne
Thu, 15 Dec 22
74/75

Comments: 40 pages, 14 figures. GitHub repository: this https URL

Aspects of Inflation and Cosmology in Non-Minimally Coupled and $R^{2}$ Palatini Gravity [CL]

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http://arxiv.org/abs/2212.06749


This thesis presents research exploring aspects of inflation and cosmology in the context of inflation models in which an inflaton is non-minimally coupled to the Ricci scalar, or is considered in conjunction with a term quadratic in the Ricci scalar. We consider a $\phi^{2}$ Palatini inflation model in $R^{2}$ gravity and investigate whether this model can overcome some of the problems of the original $\phi^{2}$ chaotic inflation model. We investigate the compatibility of this model with the observed CMB when treated as an effective theory of inflation in quantum gravity by examining the constraints on the model parameters arising due to Planck-suppressed potential corrections and reheating. Additionally, we consider two possible reheating channels and assess their viability in relation to the constraints on the size of the coupling to the $R^{2}$ term. We present an application of the Affleck-Dine mechanism, in which quadratic $B$-violating potential terms generate the asymmetry, with a complex inflaton as the Affleck-Dine field. We derive the $B$ asymmetry generated in the inflaton condensate analytically and numerically. We use the present-day asymmetry to constrain the size of the $B$-violating mass term and derive an upper bound on the inflaton mass in order for the Affleck-Dine dynamics to be compatible with non-minimally coupled inflation in the metric and Palatini formalisms. We demonstrate the existence of a new class of inflatonic Q-balls in a non-minimally coupled Palatini inflation model, through an analytical derivation of the Q-ball equation and numerical confirmation of the existence of solutions, and derive a range of the inflaton mass squared within which the model can inflate and produce Q-balls. We derive analytical estimates of the properties of these Q-balls, explore the effects of curvature, and discuss observational signatures of the model.

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K. Lloyd-Stubbs
Wed, 14 Dec 22
63/69

Comments: PhD Thesis, 286 pages, 28 figures

From Cosmic Inflation and Matter Creation to Dark Matter – Journey of the Inflaton? [CL]

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http://arxiv.org/abs/2212.06117


A scenario of the inflaton evolution from cosmic inflation and matter creation to dark energy/dark matter today is presented. To start with, a model of the inflationary phase of the inflaton is discussed. The inflaton rolls down a simple quadratic hilltop potential along with matter creation, following an exact tracking solution of its dynamics. Being dragged down by the presence of matter, it rolls down slowly and naturally ending inflation as the universe stops accelerating due to the presence of matter. The model predictions for the standard metrics such as scalar/tensor spectral indexes and tensor to scalar ratio are fully consistent with the current CMB limits. The quadratic potential could be extended to complete a potential hill subsequent to inflation. The evolution of inflaton discussed recently is consistent with this picture of its journey from cosmic inflation to dark matter today.

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B. Balakrishna
Tue, 13 Dec 22
13/105

Comments: arXiv admin note: text overlap with arXiv:2210.15475

Left-Right Symmetry Breaking and Gravitational Waves : A Tale of Two Phase Transitions [CEA]

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http://arxiv.org/abs/2212.05829


We study possible ways gravitational waves (GW) get sourced in a theory with minimal left-right symmetry breaking. First order phase transitions generically lead to gravitational waves sourced by bubble collisions, while second order phase transitions (SOPT) do not. Interesting variants on the standard classification of phase transitions occur due to the breaking of discrete parity combined with the limitation of light cone in the early Universe. If local effective potential signals SOPT or a cross over, breaking of discrete parity in conjunction with finiteness of the causal horizon leads to a \textsl{causal horizon limited} second order phase transition, which results in domain walls separating left-like and right-like domains. On the other hand for the case of usual first order phase transition (FOPT), we get the usual signal from spontaneously created bubbles, but also, as we argue from a lingering late time domain wall structure separating the two types of vacua. Thus both FOPT and putative SOPT give rise to distinct features in the spectrum of GW. The signatures are testable via experiments such as IPTA, and DECIGO and LISA. Finally we point out that a version of the left-right symmetric model which separates parity breaking from gauge symmetry breaking is also subject to domain wall formation and amenable to GW observations.

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Z. Borboruah and U. Yajnik
Tue, 13 Dec 22
18/105

Comments: 36 pages, 23 total figures including subfigures

Towards a reliable reconstruction of the power spectrum of primordial curvature perturbation on small scales from GWTC-3 [CEA]

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http://arxiv.org/abs/2212.05516


Primordial black holes (PBHs) can be both candidates of dark matter and progenitors of binary black holes (BBHs) detected by the LIGO-Virgo-KAGRA collaboration. Since PBHs could form in the very early Universe through the gravitational collapse of primordial density perturbations, the population of BBHs detected by gravitational waves encodes much information on primordial curvature perturbation. In this work, we take a reliable and systematic approach to reconstruct the power spectrum of the primordial curvature perturbation from GWTC-3, under the hierarchical Bayesian inference framework, by accounting for the measurement uncertainties and selection effects. In addition to just considering the single PBH population model, we also report the results considering the multi-population model, i.e., the mixed PBH and astrophysical black hole binaries model. We find that the maximum amplitude of the reconstructed power spectrum of primordial curvature perturbation can be $\sim2.5\times10^{-2}$ at $\mathcal{O}(10^{5})~\rm Mpc^{-1}$ scales, which is consistent with the PBH formation scenario from inflation at small scales.

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L. Zheng, Z. Li, Z. Chen, et. al.
Tue, 13 Dec 22
46/105

Comments: N/A

On de Sitter Spacetime and String Theory [CL]

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http://arxiv.org/abs/2212.06086


We review various aspects of de Sitter spacetime in string theory: its status as an effective field theory spacetime solution, its relation to the vacuum energy problem in string theory, its (global) holographic definition in terms of two entangled and non-canonical conformal field theories, as well as a realization of a realistic de Sitter universe endowed with the observed visible matter and the necessary dark sector in order to reproduce the realistic cosmological structure. In particular, based on the new insight regarding the cosmological constant problem in string theory, we argue that in a doubled, T-duality-symmetric, phase-space-like and non-commutative generalized-geometric formulation, string theory can naturally lead to a small and positive cosmological constant that is radiatively stable and technically natural. Such a formulation is fundamentally based on a quantum spacetime, but in an effective spacetime description of this general formulation of string theory, the curvature of the dual spacetime is the cosmological constant of the observed spacetime, while the size of the dual spacetime is the gravitational constant of the same observed spacetime. Also, the three scales associated with intrinsic non-commutativity of string theory, the cosmological constant scale and the Planck scale, as well as the Higgs scale, can be arranged to satisfy various seesaw-like formulae. Along the way, we show that these new features of string theory can be implemented in a particular deformation of cosmic-string-like models.

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P. Berglund, T. Hübsch and D. Minic
Tue, 13 Dec 22
59/105

Comments: 116 pages, 4 figures

Non-equilibrium dynamics of Axion-like particles: the quantum master equation [CEA]

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http://arxiv.org/abs/2212.05161


We study the non-equilibrium dynamics of Axion-like particles (ALP) coupled to Standard Model degrees of freedom in thermal equilibrium. The Quantum Master Equation (QME) for the (ALP) reduced density matrix is derived to leading order in the coupling of the (ALP) to the thermal bath, but to \emph{all} orders of the bath couplings to degrees of freedom within or beyond the Standard Model other than the (ALP). The (QME) describes the damped oscillation dynamics of an initial misaligned (ALP) condensate, thermalization with the bath, decoherence and entropy production within a unifying framework. The (ALP) energy density $\mathcal{E}(t)$ features two components: a cold'' component from the misaligned condensate and ahot” component from thermalization with the bath, with $\mathcal{E}(t)= \mathcal{E}{c}\,e^{-\gamma(T)\,t}+\mathcal{E}{h}(1-e^{-\gamma(T)\,t})$ thus providing a “mixed dark matter” scenario. Relaxation of the (ALP) condensate, thermalization, decoherence and entropy production occur on similar time scales. An explicit example with (ALP)-photon coupling, valid post recombination yields a relaxation rate $\gamma(T)$ with a substantial enhancement from thermal emission and absorption. A misaligned condensate is decaying at least since recombination and on the same time scale thermalizing with the cosmic microwave background (CMB). Possible consequences for birefringence of the (CMB) and (ALP) contribution to the effective number of ultrarelativistic species and galaxy formation are discussed.

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S. Cao and D. Boyanovsky
Tue, 13 Dec 22
67/105

Comments: 28 pages

Black hole solutions in the quadratic Weyl conformal geometric theory of gravity [CL]

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http://arxiv.org/abs/2212.05542


We consider numerical black hole solutions in the Weyl conformal geometry, and its associated conformally invariant Weyl quadratic gravity. In this model Einstein gravity (with a positive cosmological constant) is recovered in the spontaneously broken phase of Weyl gravity, after the Weyl gauge field ($\omega _{\mu}$) becomes massive through a Stueckelberg mechanism, and it decouples. As a first step in our investigations we write down the conformally invariant gravitational action, containing a scalar degree of freedom, and the Weyl vector. The field equations are derived from the variational principle in the absence of matter. By adopting a static spherically symmetric geometry, the vacuum field equations for the gravitational, scalar, and Weyl fields are obtained. After reformulating the field equations in a dimensionless form, and by introducing a suitable independent radial coordinate, we obtain their solutions numerically. We detect the formation of a black hole from the presence of a Killing horizon for the timelike Killing vector in the metric tensor components, indicating the existence of the singularity in the metric. Several models, corresponding to different functional forms of the Weyl vector, are considered. An exact black hole model, corresponding to a Weyl vector having only a radial spacelike component, is also obtained. The thermodynamic properties of the Weyl geometric type black holes (horizon temperature, specific heat, entropy and evaporation time due to Hawking luminosity) are also analyzed in detail.

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J. Yang, S. Shahidi and T. Harko
Tue, 13 Dec 22
71/105

Comments: 29 pages, 13 figures, accepted for publication in EPJC

An update on adiabatic modes in cosmology and $δ$N formalism [CEA]

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http://arxiv.org/abs/2212.05112


In this paper, we generalize the Weinberg’s procedure to determine the comoving curvature perturbation $\cal R$ to non-attractor inflationary regimes. We show that both modes of $\cal R$ are related to a symmetry of the perturbative equations in the Newtonian gauge. As a byproduct, we clarify that adiabaticity does not generally imply constancy of $\cal R$, not even in the $k\rightarrow 0$ limit. Applying this knowledge to the separate Universe approach, we find that correlators of $\delta N$ {\it do not} generically correspond to comoving curvature perturbations correlators, even at the linear level, but rather to correlators of curvature perturbations at uniform density, at least at linear level. Thus, $\delta N$ formalism does not capture information about decaying (for slow-roll) or growing (beyond slow-roll) modes of $\cal R$. The latter being the only interesting mode for models of inflation related to primordial black holes formation.

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D. Cruces, C. Germani and A. Palomares
Tue, 13 Dec 22
99/105

Comments: 15 pages, 1 figure

Growth of Cosmic Structure [CEA]

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http://arxiv.org/abs/2212.05003


We review one of the most fruitful areas in cosmology today that bridge theory and data – the temporal growth of large-scale structure. We go over the growth’s physical foundations, and derive its behavior in simple cosmological models. While doing so, we explain how measurements of growth can be used to understand theory. We then review how some of the most mature cosmological probes – galaxy clustering, gravitational lensing, the abundance of clusters of galaxies, cosmic velocities, and cosmic microwave background – can be used to probe the growth of structure. We report the current constraints on growth, which are summarized as measurements of the parameter combination $f\sigma_8$ as a function of redshift, or else as the mass fluctuation amplitude parameter $S_8$. We finally illustrate several statistical approaches, ranging from the “growth index” parameterization to more general comparisons of growth and geometry, that can sharply test the standard cosmological model and indicate the presence of modifications to general relativity.

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D. Huterer
Mon, 12 Dec 22
39/52

Comments: Invited review for The Astronomy and Astrophysics Review, aimed at a non-expert; 29 pages + references

Exploring High Frequency Gravitational Waves with Magnons [CL]

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http://arxiv.org/abs/2212.04094


Detecting gravitational waves with a frequency higher than 10 kHz requires a new idea. In previous papers, we proposed magnon gravitational wave detectors and gave the first limit on GHz gravitational waves by reinterpreting the existing data of axion dark matter experiments. In this paper, we show that the sensitivity can be improved by constructing the detector specific to gravitational waves. In particular, we employ an infinite sum of terms in the expansion of Fermi normal coordinates to probe gravitational waves with a wavelength comparable to the detector size. As a consequence, we obtain the sensitivity around $h_c \sim 10^{-20}$.

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A. Ito and J. Soda
Fri, 9 Dec 22
67/75

Comments: 13 pages, 2 figures

Primordial black holes generated by the non-minimal spectator field [CEA]

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http://arxiv.org/abs/2212.03577


In this paper, we propose a model in which a spectator field non-minimally couples to an inflaton field and the power spectrum of the perturbation of the spectator field at small scales is dramatically enhanced by the sharp feature in the form of non-minimal coupling. At or after the end of inflation, the perturbation of the spectator field is converted into curvature perturbation and leads to the formation of primordial black holes (PBHs). Furthermore, for example, we consider three phenomenological models for generating PBHs with mass function peaked at $\sim10^{-12}M_\odot$ and representing all the cold dark matter in our Universe and find that the scalar induced gravitational waves generated by the curvature perturbation can be detected by the future space-borne gravitational-wave detectors such as Taiji, TianQin and LISA.

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D. Meng, C. Yuan and Q. Huang
Thu, 8 Dec 22
30/63

Comments: 15 pages and 4 figures

Model independent bounds for the number of $e$-folds during the evolution of the universe [CL]

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http://arxiv.org/abs/2212.03730


We present a simple procedure to obtain universal bounds for quantities of cosmological interest, such as the number of $e$-folds during inflation, reheating, and radiation, as well as the reheating temperature. The main assumption is to represent each of the various epochs of evolution of the universe as being due to a single substance changing instantaneously into the next, describing a new era of evolution of the universe. This assumption, commonly used to obtain solutions of the Friedmann equations for simple cosmological models, is implemented here to find model-independent bounds on cosmological quantities of interest. In particular, we find that the bound $N_k\approx 56$ for $-\frac{1}{3} < \omega_{re} < \frac{1}{3}$ is very robust as an upper bound on the number of $e$-folds during inflation and also as a lower bound when $\omega_{re} > \frac{1}{3}$, where $\omega_{re}$ is the effective equation of state parameter during reheating. These are model-independent results that any single-field model of inflation should satisfy. As an example, we illustrate the two approaches with the basic $\alpha$ attractor model and show how they complement each other.

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G. German, R. Quaglia and A. Colorado
Thu, 8 Dec 22
34/63

Comments: 17 pages, 3 figures, 2 tables

Modified gravity and cosmology with nonminimal (derivative) coupling between matter and the Einstein tensor [CL]

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http://arxiv.org/abs/2212.03821


We construct new classes of modified theories in which the matter sector couples with the Einstein tensor, namely we consider direct couplings of the latter to the energy-momentum tensor, and to the derivatives of its trace. We extract the general field equations and we apply them in a cosmological framework, obtaining the Friedmann equations, whose extra terms give rise to an effective dark energy sector. At the background level we show that we can successfully describe the usual thermal history of the universe, with the sequence of matter and dark-energy epochs, while the dark-energy equation-of-state parameter can lie in the phantom regime, tending progressively to -1 at present and future times. Furthermore, we confront the theory with Cosmic Chronometer data, showing that the agreement is very good. Finally, we perform a detailed investigation of scalar and tensor perturbations, and extracting an approximate evolution equation for the matter overdensity we show that the predicted behavior is in agreement with observations.

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P. Asimakis, S. Basilakos, A. Lymperis, et. al.
Thu, 8 Dec 22
57/63

Comments: 9 pages,4 figures

Observing axions through photon ring dimming of black holes [CL]

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http://arxiv.org/abs/2212.03020


It is known that magnetic fields exist near black holes and photons can go around the black holes due to strong gravity. Utilizing these facts, we can probe hypothetical pseudoscalar particles, so-called axions. In fact, photons can be converted into axions when they propagate in a magnetic field. The conversion of such photons into axions leads to a dimming of the photon ring around the black hole shadow. We show that the photon ring dimming can occur efficiently for supermassive black holes. Remarkably, it turns out that the maximal dimming rate of the photon ring is 25%. In the case of M87$^*$, the dimming could be around 10% in the X-ray and gamma-ray bands. The frequency band and the magnitude of the dimming depend on the axion-photon coupling and axion mass. Hence, the distorted spectrum of the photon ring provides a novel tool for detecting axions.

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K. Nomura, K. Saito and J. Soda
Wed, 7 Dec 22
2/74

Comments: 17 pages, 4 figures

Stringent Pulsar Timing Bounds on Light Scalar Couplings to Matter [CL]

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http://arxiv.org/abs/2212.03098


Pulsar Timing constraints on scalar-tensor theories with conformal and disformal couplings to matter are discussed. Reducing the dynamics to the motion in the centre of mass frame and using the mean anomaly parametrisation, we find the first post-Newtonian corrections induced by the conformal and disformal interactions in the form of a generalized quasi-Keplerian solution. We also derive the radiation reaction force due to scalar radiation and the corresponding Post-Keplerian Parameters (PKP). We use different pulsar time of arrival (TOA) data sets to probe the scalar corrections to the PKP. In particular, we focus on systems with large orbital frequencies as the contributions to the PKP terms induced by the disformal coupling are sensitive to higher frequencies. We find that the most constraining pulsar timing events are PSR B1913+16 and the double pulsar PSR J0737-3039A/B, being stronger than the Cassini bound on the conformal coupling obtained from the Shapiro effect in the solar system. The combined constraints using other pulsar events give an upper bound on the conformal coupling $\beta^2 < 2.3 \cdot 10^{-5}$ and a lower bound on the disformal coupling scale of $\Lambda \sim 1 \ {\rm MeV}$ which is comparable to the Cassini bound and to the GW-170817 constraints respectively. Future measurements for pulsar timing with black hole companions are also discussed.

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D. Benisty, P. Brax and A. Davis
Wed, 7 Dec 22
16/74

Comments: 17 pages, 9 figures

Large Deviations in the Early Universe [CL]

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http://arxiv.org/abs/2212.02535


Fluctuations play a critical role in cosmology. They are relevant across a range of phenomena from the dynamics of inflation to the formation of structure. In many cases, these fluctuations are coarse grained and follow a Gaussian distribution as a consequence of the Central Limit Theorem. Yet, some classes of observables are dominated by rare fluctuations and are sensitive to the details of the underlying microphysics. In this paper, we argue that the Large Deviation Principle can be used to diagnose when one must to appeal to the fundamental description. Concretely, we investigate the regime of validity for the Fokker-Planck equation that governs Stochastic Inflation. For typical fluctuations, this framework leads to the central limit-type behavior expected of a random walk. However, fluctuations in the regime of the Large Deviation Principle are determined by instanton-like saddle points accompanied by a new energy scale. When this energy scale is above the UV cutoff of the EFT, the tail is only calculable in the microscopic description. We explicitly demonstrate this phenomenon in the context of determining the phase transition to eternal inflation, the distribution of scalar field fluctuations in de Sitter, and the production of primordial black holes.

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T. Cohen, D. Green and A. Premkumar
Wed, 7 Dec 22
17/74

Comments: 32 pages + references, 3 figures

Spatially Homogeneous Universes with Late-Time Anisotropy [CEA]

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http://arxiv.org/abs/2212.03234


The Cosmological Principle asserts that on sufficiently large scales the universe is homogeneous and isotropic on spatial slices. Challenging this principle requires a departure from the FLRW ansatz. In this paper we analyse the cosmological evolution of spatially homogeneous but anisotropic universes in which only two of the three space dimensions are maximally symmetric, namely the closed Kantowski-Sachs universe and the open axisymmetric Bianchi type III universe. These models are characterised by two scale factors and we study their evolution in universes with radiation, matter and a cosmological constant. In all cases, the two scale factors evolve differently and this anisotropy leads to a lensing effect in the propagation of light. We derive explicit formulae for computing redshifts, angular diameter distances and luminosity distances and discuss the predictions of these models in relation to observations for type Ia supernovae and the CMB.

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A. Constantin, T. Harvey, S. Hausegger, et. al.
Wed, 7 Dec 22
52/74

Comments: N/A

Ultra High Energy Cosmic Rays — an Overview [HEAP]

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http://arxiv.org/abs/2212.01600


We review the main experimental evidences on ultra high energy cosmic rays and their implications in the physics of these extremely energetic particles, also in connection with dark matter and cosmology. We discuss the basis of theoretical models aiming at explaining observations, highlighting the most relevant open questions in this fascinating field of research.

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R. Aloisio
Tue, 6 Dec 22
61/87

Comments: 8 pages, 11 figures, invited review talk given at the 12th Cosmic Rays International Seminar, CRIS 2022, 12-16 September 2022, Naples, Italy

The density of state method for first-order phase transitions in Yang-Mills theories [CL]

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http://arxiv.org/abs/2212.01074


Lattice Field Theory can be used to study finite temperature first-order phase transitions in new, strongly-coupled gauge theories of phenomenological interest. Metastable dynamics arising in proximity of the phase transition can lead to large, uncontrolled numerical errors when analysed with standard methods. In this contribution, we discuss a prototype lattice calculation in which the first-order deconfinement transition in the strong Yang-Mills sector of the standard model is analysed using a novel lattice method, the logarithmic linear relaxation algorithm. This method provides a determination of the density of states of the system with exponential error suppression. Thermodynamic observables can be reconstructed with a controlled error, providing a promising direction for accurate numerical predictions.

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D. Mason, B. Lucini, M. Piai, et. al.
Mon, 5 Dec 22
4/63

Comments: 10 pages, 6 figures; contribution to the proceedings of the 39th Lattice conference, 8th-13th August 2022, Bonn, Germany. arXiv admin note: text overlap with arXiv:2211.10373

Transitioning from a bounce to $R^2$ inflation [CL]

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http://arxiv.org/abs/2212.01093


Non-singular bouncing cosmologies are well–motivated models for the early universe. Recent observational data are consistent with positive spatial curvature and allow for a natural collapsing and bouncing phase in the very early universe. Additionally, bouncing cosmologies have the potential to rectify conceptual shortcomings identified in the theory of inflation, such as the singularity problem. In this paper we present a classical bouncing model in the context of modified gravity, including an $R^2$-term in the action. We show that after the bounce, the universe enters naturally a period of inflation, driven by the $R^2$–term. We analyse the stability of the model and find that the scalaron assists the stability of the model.

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R. Daniel, M. Campbell, C. Bruck, et. al.
Mon, 5 Dec 22
30/63

Comments: 19 pages, 8 figures

Regularization in cosmological spacetimes without infrared distortions [CL]

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http://arxiv.org/abs/2212.01078


We reexamine the regularization of the two-point function of a scalar field in a Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime. Adiabatic regularization provides a set of subtraction terms in momentum space that successfully remove its ultraviolet divergences at coincident points, but can significantly distort the power spectrum at infrared scales, especially for light fields. In this work we propose, by using the intrinsic ambiguities of the renormalization program, a new set of subtraction terms that minimize the distortions for scales $k \lesssim M$, with $M$ an arbitrary mass scale. Our method is consistent with local covariance and equivalent to general regularization methods in curved spacetime. We apply our results to the regularization of the power spectrum in de Sitter space: while the adiabatic scheme yields exactly $\Delta_{\phi}^{\rm (reg)} = 0$ for a massless field, our proposed prescription recovers the standard scale-invariant result $\Delta_{\phi}^{\rm (reg)} \simeq H^2 /(4\pi^2)$ at super-horizon scales.

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A. Ferreiro and F. Torrenti
Mon, 5 Dec 22
34/63

Comments: 5 pages + references, 1 figure

Numerical simulations of inflationary dynamics: slow-roll and beyond [CL]

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http://arxiv.org/abs/2212.00529


Cosmic inflation is a period of rapid accelerated expansion of space in the very early universe. During inflation, vacuum quantum fluctuations are amplified and stretched to cosmological scales which seed the fluctuations in the cosmic microwave background as well as the large-scale structure of our universe. Large quantum fluctuations may lead to the formation of primordial black holes (PBHs) in the post-inflationary universe. Numerical simulations of the inflationary dynamics are presented here for a single canonical scalar field minimally coupled to gravity. We spell out the basic equations governing the inflationary dynamics in terms of cosmic time $t$ and define a set of dimensionless variables convenient for numerical analysis. We then provide a link to our simple numerical Python code on GitHub that can be used to simulate the background dynamics as well as the evolution of linear perturbations during inflation. The code computes both scalar and tensor power spectra for a given inflaton potential $V(\phi)$. We discuss a concrete algorithm to use the code for various purposes, especially for computing the enhanced scalar power spectrum in the context of PBH formation. We intend to extend the framework to simulate the dynamics of a number of different quantities, including the computation of scalar-induced second-order tensor power spectrum in the revised version of this manuscript in the near future.

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S. Bhatt, S. Mishra, S. Basak, et. al.
Fri, 2 Dec 22
51/81

Comments: 39 pages, 20 figures, GitHub link to codes provided in the paper, comments and suggestions are welcome

The Cosmic Neutrino Background Distribution on the Surface of the Earth [CL]

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http://arxiv.org/abs/2212.00036


We argue that the reflection of relic neutrinos from the surface of the Earth results in a significant local $\nu-\bar{\nu}$ asymmetry, far exceeding the expected primordial lepton asymmetry. The net fractional electron neutrino number $\frac{n_{\nu_e}-n_{\bar{\nu}e}}{n{\nu_e}}$ is up to $\mathcal{O}(10^5) \sqrt{\frac{m_\nu}{0.1~\text{eV}}}$ larger than that implied by the baryon asymmetry. This enhancement is due to the weak 4-Fermi repulsion of the $\nu_e$ from ordinary matter which slows down the $\nu_e$ near the Earth’s surface, and to the resulting evanescent neutrino wave that penetrates below the surface. This repulsion thus creates a net $\nu_e$ overdensity in a shell $\sim 7~\text{meters} \sqrt{\frac{0.1~\text{eV}}{m_\nu}}$ thick around the Earth’s surface. Similarly the repulsion between $\bar{\nu}\mu$ or $\bar{\nu}\tau$ and ordinary matter creates an overdensity of $\bar{\nu}_{\mu, \tau}$ of similar size. These local enhancements increase the size of $\mathcal{O}(G_F)$ torques of the $C\nu B$ on spin-polarized matter by a factor of order $10^5$. In addition, they create a gradient of the net neutrino density which naturally provides a way out of the forty-year-old “no-go” theorems on the vanishing of $\mathcal{O}(G_F)$ forces. The torque resulting from such a gradient force can be $10^8$ times larger than that of earlier proposals. Although the size of these effects is still far from current reach, they may point to new directions for $C\nu B$ detection.

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A. Arvanitaki and S. Dimopoulos
Fri, 2 Dec 22
53/81

Comments: 14 pages, 6 figures

Realization of Dirac quantization in loop quantum gravity [CL]

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http://arxiv.org/abs/2212.00203


The system of gravity coupled to the non-rotational dust field is studied at both classical and quantum levels. The scalar constraint of the system can be written in the form of a true physical Hamiltonian with respect to the dust time. In the framework of loop quantum gravity, the scalar constraint is promoted to a well-defined operator in a suitable Hilbert space of the coupled system, such that the physical Hamiltonian becomes a symmetric operator. By the deparametrized form, a general expression of the solutions to the quantum scalar constraint is obtained, and the observables on the space of solutions can be constructed. Moreover, the Dirac quantization procedure can be fully carried out in loop quantum gravity by this system.

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X. Zhang and Y. Ma
Fri, 2 Dec 22
59/81

Comments: 6 pages

Collinear and triangular solutions to the three-body problem in the parameterized post-Newtonian formalism [CL]

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http://arxiv.org/abs/2212.00198


This paper investigates the three-body problem in the parameterized post-Newtonian (PPN) formalism, for which we focus on a coplanar case in a class of fully conservative theories characterized by the Eddington-Robertson parameters $\beta$ and $\gamma$. It is shown that there can still exist a collinear equilibrium configuration and a triangular one, each of which is a generalization of the post-Newtonian equilibrium configuration in general relativity. The collinear configuration can exist for arbitrary mass ratio, $\beta$, and $\gamma$. On the other hand, the PPN triangular configuration depends on the nonlinearity parameter $\beta$ but not on $\gamma$. For any value of $\beta$, the equilateral configuration is possible, if and only if three finite masses are equal or two test masses orbit around one finite mass. For general mass cases, the PPN triangle is not equilateral as in the post-Newtonian case. It is shown also that the PPN displacements from the standard Lagrange points $L_1$, $L_2$ and $L_3$ depend on $\beta$ and $\gamma$, whereas those to $L_4$ and $L_5$ rely only on $\beta$.

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Y. Nakamura and H. Asada
Fri, 2 Dec 22
79/81

Comments: 8 pages, 2 figures

Large-scale geometry of the Universe [CEA]

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http://arxiv.org/abs/2211.16893


The large scale geometry of the late Universe can be decomposed as R$\times {\Sigma}_3$, where R stands for cosmic time and ${\Sigma}_3$ is the three dimensional spatial manifold. We conjecture that the spatial geometry of the Universe’s spatial section ${\Sigma}_3$ conforms with the Thurston-Perelman theorem, according to which the geometry of $\Sigma_3$ is either one of the eight geometries from the Thurston geometrization conjecture, or a combination of Thurston geometries smoothly sewn together. We assume that topology of individual geometries plays no observational role, i.e. the size of individual geometries is much larger than the Hubble radius today. We investigate the dynamics of each of the individual geometries by making use of the simplifying assumption that our local Hubble patch consists of only one such geometry, which is approximately homogeneous on very large scales, but spatial isotropy is generally violated. Spatial anisotropies grow in time in decelerating universes, but they decay in accelerating universes. The thus-created anisotropy problem can be solved by a period of primordial inflation, akin to how the flatness problem is solved. Therefore, as regards Universe’s large scale geometry, any of the Thurston’s geometries should be considered on a par with Friedmann’s geometries. We consider two observational methods that can be used to test our conjecture: one based on luminosity distance and one on angular diameter distance measurements, but leave for the future their detailed forecasting implementations.

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Y. Awwad and T. Prokopec
Thu, 1 Dec 22
4/85

Comments: 38 pages, 36 figures

Probing new physics on the horizon of black holes with gravitational waves [CL]

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http://arxiv.org/abs/2211.16900


Black holes are the most compact objects in the Universe. According to general relativity, black holes have a horizon that hides a singularity where Einstein’s theory breaks down. Recently, gravitational waves opened the possibility to probe the existence of horizons and investigate the nature of compact objects. This is of particular interest given some quantum-gravity models which predict the presence of horizonless and singularity-free compact objects. Such exotic compact objects can emit a different gravitational-wave signal relative to the black hole case. In this thesis, we analyze the stability of horizonless compact objects, and derive a generic framework to compute their characteristic oscillation frequencies. We provide an analytical, physically-motivated template to search for the gravitational-wave echoes emitted by these objects in the late-time postmerger signal. Finally, we infer how extreme mass-ratio inspirals observable by future gravitational-wave detectors will allow for model-independent tests of the black hole paradigm.

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E. Maggio
Thu, 1 Dec 22
45/85

Comments: PhD thesis, 160 pages

The one-loop bispectrum of galaxies in redshift space from the Effective Field Theory of Large-Scale Structure [CEA]

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http://arxiv.org/abs/2211.17130


We derive the kernels and the Effective Field Theory of Large-Scale Structure counterterms for the one-loop bispectrum of dark matter and of biased tracers in real and redshift space. This requires the expansion of biased tracers up to fourth order in fluctuations. In the process, we encounter several subtleties related to renormalization. One is the fact that, in renormalizing the momentum, a local counterterm contributes non-locally. A second subtlety is related to the renormalization of local products of the velocity fields, which need to be expressed in terms of the renormalized velocity in order to preserve Galilean symmetry. We check that the counterterms we identify are necessary and sufficient to renormalize the one-loop bispectrum at leading and subleading order in the derivative expansion. The kernels that we originally present here have already been used for the first analyses of the one-loop bispectrum in BOSS data [1, 2].

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G. D’Amico, Y. Donath, M. Lewandowski, et. al.
Thu, 1 Dec 22
47/85

Comments: 39 + 27 pages, ancillary Mathematica file in “Other formats”

Centenary of Alexander Friedmann's Prediction of the Universe Expansion and the Quantum Vacuum [CL]

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http://arxiv.org/abs/2211.17101


We review the main scientific pictures of the universe developed from ancient times to Albert Einstein and underline that all of them treated the universe as a stationary system with unchanged physical properties. In contrast to this, 100 years ago Alexander Friedmann predicted that the universe expands starting from the point of infinitely large energy density. We briefly discuss the physical meaning of this prediction and its experimental confirmation consisting of the discovery of redshift in the spectra of remote galaxies and relic radiation. After mentioning the horizon problem in the theory of the hot universe, the inflationary model is considered in connection with the concept of quantum vacuum as an alternative to the inflaton field. The accelerated expansion of the universe is discussed as powered by the cosmological constant originating from the quantum vacuum. The conclusion is made that since Alexander Friedmann’s prediction of the universe expansion radically altered our picture of the world in comparison with the previous epochs, his name should be put on a par with the names of Ptolemy and Copernicus.

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G. Klimchitskaya and V. Mostepanenko
Thu, 1 Dec 22
63/85

Comments: 16 pages, 1 figure

Islands in the Fluid: Islands are Common in Cosmology [CL]

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http://arxiv.org/abs/2211.16600


We discuss the possibility of entanglement islands in cosmological spacetimes with a general perfect fluid with an equation of state $w$. We find that flat universes with time-symmetric slices where the Hubble parameter vanishes always have islands on that slice. We then move away from such slices, considering still universes with a general perfect fluid. Under the local thermal equilibrium assumption, the comoving entropy density $s_c$ is constant. As a result, the conditions for an island become an inequality between the energy density (or Hubble parameter) and the temperature at some time of normalization. The consequences are that islands can exist for practically all fluids that are not radiation, i.e. $w\neq 1/3$. We also discuss the ramifications of our results for universes with spatial curvature. Finally, we show that islands occur in the Simple Harmonic Universe model which has no classical singularity at the background level, in contrast to all previous examples where islands occurred only in space-times with singularities.

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I. Ben-Dayan, M. Hadad and E. Wildenhain
Thu, 1 Dec 22
81/85

Comments: 26 pages, 5 figures

Freezing-In Gravitational Waves [CL]

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http://arxiv.org/abs/2211.16513


The thermal plasma in the early universe produced a stochastic gravitational wave (GW) background, which peaks today in the microwave regime and was dubbed the cosmic gravitational microwave background (CGMB). In previous works only single graviton production processes that contribute to the CGMB have been considered. Here we also investigate graviton pair production processes and show that these can lead to a significant contribution if the maximum temperature of the universe in units of Planck mass divided by the internal coupling in the heat bath is large enough. As the dark matter freeze-in production mechanism is conceptually very similar to the GW production mechanism from the primordial thermal plasma, we refer to the latter as “GW freeze-in production”. We also show that quantum gravity effects arising in single graviton production are smaller than the leading order result by a factor of the square of the ratio between the maximum temperature and the Planck mass. In our work we explicitly compute the CGMB spectrum within a scalar model with quartic interaction.

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J. Ghiglieri, J. Schütte-Engel and E. Speranza
Thu, 1 Dec 22
82/85

Comments: 18 pages, 6 figures

Latest data constraint of some parameterized dark energy models [CEA]

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http://arxiv.org/abs/2211.15881


Using various latest cosmological datasets including Type-Ia supernovae, cosmic microwave background radiation, baryon acoustic oscillations, and estimations of the Hubble parameter, we test some dark energy models with parameterized equations of state and try to distinguish or select observation-preferred models. We obtain the best fitting results of the six models and calculate their values of the Akaike Information Criteria and Bayes Information Criterion. And we can distinguish these dark energy models from each other by using these two information criterions. However, the $\Lambda $CDM model remains the best fit model. Furthermore, we perform geometric diagnostics including statefinder and Om diagnostics to understand the geometric behaviour of the dark energy models. We find that the six DE models can be distinguished from each other and from $\Lambda$CDM, Chaplygin gas, quintessence models after the statefinder and Om diagnostics were performed. Finally, we consider the growth factor of the dark energy models with comparison to $\Lambda $CDM model. Still, we find the models can be distinguished from each other and from $\Lambda $CDM model through the growth factor approximation.

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J. Yang, X. Fan, C. Feng, et. al.
Wed, 30 Nov 22
50/81

Comments: 23 pages, 6 figures, to be published in CPL

Primordial Black Hole Formation during a Strongly Coupled Crossover [CEA]

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http://arxiv.org/abs/2211.15674


The final mass distribution of primordial black holes is sensitive to the equation of state of the Universe at the scales accessible by the power spectrum. Motivated by the presence of phase transitions in several beyond the Standard Model theories, some of which are strongly coupled, we analyse the production of primordial black holes during such phase transitions, which we model using the gauge/gravity duality. We focus in the (often regarded as physically uninteresting) case for which the phase transition is just a smooth crossover. We find an enhancement of primordial black hole production in the range $M_{\rm{PBH}}\in[10^{-16},10^{-6}]M_{\odot}$.

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A. Escrivà and J. Subils
Wed, 30 Nov 22
75/81

Comments: 5 pages + references, 4 figures

FeynMG: a FeynRules extension for scalar-tensor theories of gravity [CL]

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http://arxiv.org/abs/2211.14300


The ability to represent perturbative expansions of interacting quantum field theories in terms of simple diagrammatic rules has revolutionized calculations in particle physics (and elsewhere). Moreover, these rules are readily automated, a process that has catalysed the rise of symbolic algebra packages. However, in the case of extended theories of gravity, such as scalar-tensor theories, it is necessary to precondition the Lagrangian to apply this automation or, at the very least, to take advantage of existing software pipelines. We present a Mathematica code FeynMG, which works in conjunction with the well-known package FeynRules, to do just that: FeynMG takes as inputs the FeynRules model file for a non-gravitational theory and a user-supplied gravitational Lagrangian. FeynMG provides functionality that inserts the minimal gravitational couplings of the degrees of freedom specified in the model file, determines the couplings of the additional tensor and scalar degrees of freedom (the metric and the scalar field from the gravitational sector), and preconditions the resulting Lagrangian so that it can be passed to FeynRules, either directly or by outputting an updated FeynRules model file. The Feynman rules can then be determined and output through FeynRules, using existing universal output formats and interfaces to other analysis packages.

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S. Muñoz, E. Copeland, P. Millington, et. al.
Tue, 29 Nov 22
9/80

Comments: 35 pages, 1 figure, GitLab link: this https URL

Completely Dark Matter from Rapid-Turn Multifield Inflation [CL]

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http://arxiv.org/abs/2211.14323


We study cosmological gravitational particle production as applied to “rapid-turn” models of inflation involving two scalar fields. We are interested in the production of massive spin-0 particles that only interact gravitationally and provide a candidate for the dark matter. Specifically, we study two models of rapid-turn multifield inflation, motivated in part by the de Sitter swampland conjecture, that are distinguished by the curvature of field space and the presence or absence of field space ‘angular momentum’ conservation. We find that one of these models leads to insufficient particle production and cannot explain the observed dark matter relic abundance. The second model is able to explain the origin of spin-0 dark matter via gravitational production, and we identify the relevant region of parameter space that is consistent with measurements of the dark-matter relic abundance, the dark-matter-photon isocurvature perturbations, and the spectrum of curvature perturbations that is probed by cosmological observations. Our work demonstrates the compatibility of the de Sitter swampland conjecture with completely dark matter.

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E. Kolb, A. Long, E. McDonough, et. al.
Tue, 29 Nov 22
27/80

Comments: N/A

Implications of the Weak Gravity Conjecture for Tidal Love Numbers of Black Holes [CL]

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http://arxiv.org/abs/2211.14325


The Weak Gravity Conjecture indicates that extremal black holes in the low energy effective field theory should be able to decay. This criterion gives rise to non-trivial constraints on the coefficients of higher-order derivative corrections to gravity. In this paper, we investigate the tidal deformability of neutral black holes due to higher-order derivative corrections. As a case in point, we consider a correction of cubic order in the Riemann curvature tensor. The tidal Love numbers of neutral black holes receive leading-order corrections from higher-order derivative terms, since black holes in pure General Relativity have vanishing tidal Love number. We conclude that the tidal deformability of neutral black holes is constrained by the Weak Gravity Conjecture, and therefore provides a test for quantum gravity.

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V. Luca, J. Khoury and S. Wong
Tue, 29 Nov 22
41/80

Comments: 21 pages, 2 figures

The Hubble Constant Troubled by Dark Matter in Non-Standard Cosmologies [CEA]

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http://arxiv.org/abs/2211.14345


The Standard Cosmological Model has experienced tremendous success at reproducing observational data by assuming a universe dominated by a cosmological constant and dark matter in a flat geometry. However, several studies, based on local measurements, indicate that the universe is expanding too fast, in disagreement with the Cosmic Microwave Background. Taking into account combined data from CMB, Baryon Acoustic Oscillation, and type Ia Supernovae, we show that if the mechanism behind the production of dark matter particles has at least a small non-thermal origin, one can induce larger values of the Hubble rate $H_0$, within the $\Lambda$CDM, to alleviate the trouble with $H_0$. In the presence of non-standard cosmology, however, we can fully reconcile CMB and local measurements and reach $H_0=70-74\, {\rm km s^{-1} Mpc^{-1}}$.

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J. Alcaniz, J. Neto, F. Queiroz, et. al.
Tue, 29 Nov 22
44/80

Comments: 3 figures, 7 pages. Accepted for Publication in Nature Scientific Reports

Gravitational Wave Probes of Massive Gauge Bosons at the Cosmological Collider [CL]

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http://arxiv.org/abs/2211.14331


We extend the reach of the “cosmological collider” for massive gauge boson production during inflation from the CMB scales to the interferometer scales. Considering a Chern-Simons coupling between the gauge bosons and the pseudoscalar inflaton, one of the transverse gauge modes is efficiently produced and its inverse decay leaves an imprint in the primordial scalar and tensor perturbations. We study the correlation functions of these perturbations and derive the updated constraints on the parameter space from CMB observables. We then extrapolate the tensor power spectrum to smaller scales consistently taking into account the impact of the gauge field on inflationary dynamics. Our results show that the presence of massive gauge fields during inflation can be detected from characteristic gravitational wave signals encompassing the whole range of current and planned interferometers.

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X. Niu, M. Rahat, K. Srinivasan, et. al.
Tue, 29 Nov 22
48/80

Comments: 35 pages, 7 figures

Primordial black holes and gravitational waves from non-canonical inflation [CEA]

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http://arxiv.org/abs/2211.14900


Primordial black holes (PBHs) can generically form in inflationary setups through the collapse of enhanced cosmological perturbations, providing us access to the early Universe through their associated observational signatures. In the current work we propose a new mechanism of PBH production within non-canonical inflation, using a class of steep-deformed inflationary potentials compatible with natural values for the non-canonical exponents. In particular, by requiring significant PBH production we extract constraints on the non-canonical exponents. Additionally, we find that our scenario can lead to the formation of asteroid-mass PBHs, which can account for the totality of the dark matter, as well as to production of solar-mass PBHs within the LIGO/VIRGO detection band. Finally, we find that the enhanced cosmological perturbations which collapse to form PBHs can produce a stochastic gravitational-wave (GW) background induced by second-order gravitational interactions. Very interestingly, we obtain a GW signal detectable by future GW experiments, in particular by SKA, LISA and BBO.

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T. Papanikolaou, A. Lymperis, S. Lola, et. al.
Tue, 29 Nov 22
56/80

Comments: 17 pages without appendices (23 in total), 7 figures

Parity-Odd and Even Trispectrum from Axion Inflation [CL]

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http://arxiv.org/abs/2211.14324


The four-point correlation function of primordial scalar perturbations has parity-even and parity-odd contributions, and the parity-odd signal in cosmological observations is opening a novel window to look for new physics in the inflationary epoch. We study the distinct parity-odd and even prediction from the axion inflation model, in which the inflaton couples to a vector field via a Chern-Simons interaction, and the vector field is considered to be either approximately massless ($m_A \ll $ the Hubble scale $H$) or very massive ($m_A \sim H $). The parity-odd signal arises due to one transverse mode of the vector field being predominantly produced during inflation. We adopt the in-in formalism to evaluate the correlation functions. Considering the vector field mode function to be dominated by its real part up to a constant phase, we simplify the formulas for numerical computations. The numerical studies show that the massive and massless vector fields give significant parity-even signals, while the parity-odd signals are about one to two orders of magnitude smaller.

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X. Niu, M. Rahat, K. Srinivasan, et. al.
Tue, 29 Nov 22
80/80

Comments: 21 pages, 10 figures

Primordial black holes from Higgs inflation with a Gauss-Bonnet coupling [CEA]

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http://arxiv.org/abs/2211.13364


Primordial black holes (PBHs) can be the source for all or a part of today’s dark matter density. Inflation provides a mechanism for generating the seeds of PBHs in the presence of a temporal period where the velocity of an inflaton field $\phi$ rapidly decreases toward 0. We compute the primordial power spectra of curvature perturbations generated during Gauss-Bonnet (GB) corrected Higgs inflation in which the inflaton field has not only a nonminimal coupling to gravity but also a GB coupling. For a scalar-GB coupling exhibiting a rapid change during inflation, we show that curvature perturbations are sufficiently enhanced by the appearance of an effective potential $V_{\rm eff}(\phi)$ containing the structures of plateau-type, bump-type, and their intermediate type. We find that there are parameter spaces in which PBHs can constitute all dark matter for these three types of $V_{\rm eff}(\phi)$. In particular, models with bump- and intermediate-types give rise to the primordial scalar and tensor power spectra consistent with the recent Planck data on scales relevant to the observations of cosmic microwave background. This property is attributed to the fact that the number of e-foldings $\Delta N_c$ acquired around the bump region of $V_{\rm eff}(\phi)$ can be as small as a few, in contrast to the plateau-type where $\Delta N_c$ typically exceeds the order of 10.

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R. Kawaguchi and S. Tsujikawa
Mon, 28 Nov 22
1/93

Comments: 20 pages, 7 figures

Logarithmic Duality of the Curvature Perturbation [CEA]

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http://arxiv.org/abs/2211.13932


We study the comoving curvature perturbation $\mathcal{R}$ in general single-field inflation models whose potential can be approximated by a piecewise quadratic potential $V(\varphi)$ by using the $\delta N$ formalism. We find a general formula for $\mathcal{R}(\delta\varphi)$, which consists of a sum of logarithmic functions of the field perturbation $\delta\varphi$ at the point of interest, as well as of its field velocity perturbations $\delta\pi_*$ at the boundaries of each quadratic piece, which are functions of $\delta\varphi$ through the equations of motion. In some simple cases, $\mathcal{R}(\delta\varphi)$ reduces to a single logarithm, which yields either the renowned “exponential tail” of the probability distribution function of $\mathcal{R}$ or the Gumbel distribution.

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S. Pi and M. Sasaki
Mon, 28 Nov 22
25/93

Comments: 7 pages, 3 figures

A hybrid model for the dark sector [CL]

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http://arxiv.org/abs/2211.13653


Diverse cosmological and astrophysical observations strongly hint at the presence of dark matter and dark energy in the Universe. One of the main goals of Cosmology is to explain the nature of these two components. It may well be that both dark matter and dark energy have a common origin. In this paper, we develop a model in which the dark sector arises due to an interplay between two interacting scalar fields. Employing a hybrid inflation potential, we show that the model can be described as a system of a pressureless fluid coupled to a light scalar field. We discuss this setup’s cosmological consequences and the observational signatures in the cosmic microwave background radiation and the large-scale structures.

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C. Bruck, G. Poulot and E. Teixeira
Mon, 28 Nov 22
40/93

Comments: 13 pages, 10 figures

Hybrid $α$-attractors, primordial black holes and gravitational wave backgrounds [CEA]

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http://arxiv.org/abs/2211.14262


We investigate the two-stage inflation regime in the theory of hybrid cosmological $\alpha$-attractors. The spectrum of inflationary perturbations is compatible with the latest Planck/BICEP/Keck results, thanks to the attractor properties of the model. However, at smaller scales, it may have a very high peak of controllable width and position, leading to a copious production of primordial black holes (PBH) and generation of a stochastic background of gravitational waves (SGWB).

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M. Braglia, A. Linde, R. Kallosh, et. al.
Mon, 28 Nov 22
52/93

Comments: 39 pages, 12 figures

Slow-roll inflation in $f\left(R, T, R_{ab}T^{ab}\right)$ gravity [CL]

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http://arxiv.org/abs/2211.13233


In the framework of $f\left(R, T, R_{ab}T^{ab}\right)$ gravity theory, the slow-roll approximation of the cosmic inflation is investigated, where $T$ is the trace of the energy-momentum tensor $T^{ab}$, $R$ and $R_{ab}$ are the Ricci scalar and tensor, respectively. After obtaining the equations of motion of the gravitational field from the action principle in the spatially flat FLRW metric, the fundamental equations of this theory are received by introducing the inflation scalar field as the matter and taking into account only the minimum curvature-inflation coupling term. Remarkably, after taking the slow-roll approximation, the identical equations as in $f(R, T)$ gravity with a $RT$ mixing term are derived. Several potentials of interest in different domains are evaluated individually, calculating the slow-roll parameter and the e-folding number $N$. Finally, we analyze the behavior of the inflation scalar field under perturbation while ignoring the effect of metric perturbations. This research complements the slow-roll inflation in the modified theory of gravity.

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Z. Feng
Mon, 28 Nov 22
53/93

Comments: 14 pages, 1 figure

Gravitational waves radiated by magnetic galactic binaries and detection by LISA [CL]

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http://arxiv.org/abs/2211.14278


In the context of the future Laser Interferometer Space Antenna (LISA) mission, galactic binary systems of white dwarfs and neutron stars will represent the dominant source of Gravitational Waves (GWs) within the $10^{-4}-10^{-1}\,\mathrm{Hz}$ frequency band. It is expected that LISA will measure simultaneously, the GWs from more than ten thousands of these compact galactic binaries. The analysis of such a superposition of signals will represent one of the greatest challenge for the mission. Currently, in the LISA Datacode Challenge, each galactic binary is modeled as a quasi-monochromatic source of GWs. This corresponds to the circular motion of two point-masses at the 2.5 post-Newtonian approximation. If this picture is expected to be an accurate description for most of the galactic binaries that LSIA will detect, we nevertheless expect to observe eccentric systems with complex physical properties beyond the point-mass approximation. In this work, we investigate how a binary system of highly magnetic objects in quasi-circular orbit could affect the quasi-monochromatic picture of the GW signal detected by LISA. We demonstrate that the eccentricity generates additional frequency peaks at harmonics of the mean motion and that magnetism is responsible for shifting each frequency peak with respect to the case without magnetism. We provide analytical estimates and argue that LISA will be able to detect magnetism if it can measure the main peaks at two and three times the mean motion with a sufficient accuracy.

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A. Bourgoin, C. Poncin-Lafitte, S. Mathis, et. al.
Mon, 28 Nov 22
76/93

Comments: 4 pages, 1 figure, proceedings Les rencontres de Moriond

One-loop tensor power spectrum from an excited scalar field during inflation [CEA]

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http://arxiv.org/abs/2211.12766


We present a consistent one-loop calculation for the inflationary tensor power spectrum in the presence of an excited spectator scalar field using the in-in formalism. We find that the super-horizon primordial power spectrum of the tensor mode can be scale-invariantly enhanced or reduced by the loop effects of a subhorizon scalar field. Our calculation also includes the scalar-induced gravitational wave spectrum classically computed in the previous literature, which is significant only near the scales where the scalar field is amplified. The super-horizon enhancement is a higher-order effect of the interaction Hamiltonian, which can be understood as a Bogoliubov transformation introduced by nonlinear interactions. On the other hand, the scale-invariant reduction of the tensor power spectrum may occur due to the fourth-order scalar-scalar-tensor-tensor coupling. This phenomenon can be understood as the evolution of an anisotropic Bianchi type-I background in the separate universe approach. Our result suggests that large-scale measurements may indirectly test the dramatic effects of small-scale cosmological perturbations through loop corrections. This possibility opens a new ground in probing the small-scale physics of the primordial Universe through gravitational wave detectors of cosmological scales.

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A. Ota, M. Sasaki and Y. Wang
Thu, 24 Nov 22
28/71

Comments: 22 pages, 5 figures, full details of 2209.02272 and more

Gravitational radiation from binary systems in $f(R)$ gravity: A semi-classical approach [CL]

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http://arxiv.org/abs/2211.12947


The rate of energy loss and orbital period decay of quasi-stable compact binary systems are derived in $f(R)$ theory of gravity using the method of a single vertex graviton emission process from a classical source. After linearising the $f(R)$ action written in an equivalent scalar-tensor format in the Einstein frame, we identify the appropriate interaction terms between the massless spin-2 tensor mode, massive scalar mode, and the energy momentum tensor. The definition of the scalar field is related to the $f(R)$ models. Then using the interaction vertex we compute the rate of energy loss due to spin-2 quadrupole radiation, which comes out to be the same as the Peter-Mathews formula with a multiplication factor, and also the energy loss due to the scalar dipole radiation. The total energy loss is the sum of these two contributions. Our derivation is most general as it is applicable for both arbitrary eccentricity of the binary orbits and arbitrary mass of the scalar field. Using the derived theoretical formula for the period decay of the binary systems, we compare the predictions of $f(R)$ gravity and general relativity for the observations of three binary systems, i.e. Hulse-Taylor Binary, PSR J1141-6545 and PSR J1738+0333. Thus we put bound on three well-known $f(R)$ dark energy models, namely the Hu-Sawicki, the Straobinsky, and the Tsujukawa model. We get the best constraint on $f'(R_0)-1$ (where $R_0$ is the scalar curvature of the Universe at the present epoch) from the Tsujikawa model, i.e $\vert f'(R_0)-1\vert < 3.44\times 10^{-4}$. This bound is stronger than those from most of the astrophysical observations and even some cosmological observations.

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A. Narang, S. Mohanty and S. Jana
Thu, 24 Nov 22
67/71

Comments: 21 pages, 1 figure, 2 tables

One-loop tensor power spectrum from an excited scalar field during inflation [CEA]

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http://arxiv.org/abs/2211.12766


We present a consistent one-loop calculation for the inflationary tensor power spectrum in the presence of an excited spectator scalar field using the in-in formalism. We find that the super-horizon primordial power spectrum of the tensor mode can be scale-invariantly enhanced or reduced by the loop effects of a subhorizon scalar field. Our calculation also includes the scalar-induced gravitational wave spectrum classically computed in the previous literature, which is significant only near the scales where the scalar field is amplified. The super-horizon enhancement is a higher-order effect of the interaction Hamiltonian, which can be understood as a Bogoliubov transformation introduced by nonlinear interactions. On the other hand, the scale-invariant reduction of the tensor power spectrum may occur due to the fourth-order scalar-scalar-tensor-tensor coupling. This phenomenon can be understood as the evolution of an anisotropic Bianchi type-I background in the separate universe approach. Our result suggests that large-scale measurements may indirectly test the dramatic effects of small-scale cosmological perturbations through loop corrections. This possibility opens a new ground in probing the small-scale physics of the primordial Universe through gravitational wave detectors of cosmological scales.

Read this paper on arXiv…

A. Ota, M. Sasaki and Y. Wang
Thu, 24 Nov 22
10/71

Comments: 22 pages, 5 figures, full details of 2209.02272 and more

Gravitational radiation from binary systems in $f(R)$ gravity: A semi-classical approach [CL]

Posted on by

http://arxiv.org/abs/2211.12947


The rate of energy loss and orbital period decay of quasi-stable compact binary systems are derived in $f(R)$ theory of gravity using the method of a single vertex graviton emission process from a classical source. After linearising the $f(R)$ action written in an equivalent scalar-tensor format in the Einstein frame, we identify the appropriate interaction terms between the massless spin-2 tensor mode, massive scalar mode, and the energy momentum tensor. The definition of the scalar field is related to the $f(R)$ models. Then using the interaction vertex we compute the rate of energy loss due to spin-2 quadrupole radiation, which comes out to be the same as the Peter-Mathews formula with a multiplication factor, and also the energy loss due to the scalar dipole radiation. The total energy loss is the sum of these two contributions. Our derivation is most general as it is applicable for both arbitrary eccentricity of the binary orbits and arbitrary mass of the scalar field. Using the derived theoretical formula for the period decay of the binary systems, we compare the predictions of $f(R)$ gravity and general relativity for the observations of three binary systems, i.e. Hulse-Taylor Binary, PSR J1141-6545 and PSR J1738+0333. Thus we put bound on three well-known $f(R)$ dark energy models, namely the Hu-Sawicki, the Straobinsky, and the Tsujukawa model. We get the best constraint on $f'(R_0)-1$ (where $R_0$ is the scalar curvature of the Universe at the present epoch) from the Tsujikawa model, i.e $\vert f'(R_0)-1\vert < 3.44\times 10^{-4}$. This bound is stronger than those from most of the astrophysical observations and even some cosmological observations.

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A. Narang, S. Mohanty and S. Jana
Thu, 24 Nov 22
60/71

Comments: 21 pages, 1 figure, 2 tables

Quantum coherence in relativistic transport theory: applications to baryogenesis [CL]

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http://arxiv.org/abs/2211.11785


We derive field-theoretic local quantum transport equations which can describe quantum coherence. Our methods are based on Kadanoff–Baym equations derived in the Schwinger–Keldysh closed time path formalism of non-equilibrium quantum field theory. We focus on spatially homogeneous and isotropic systems and mixing fermions with a time-dependent mass and a weak coupling to a thermal plasma.
We introduce a new local approximation (LA) method and use it to derive quantum kinetic equations which can describe coherence and also include effects of the spectral width. The method is based on a local ansatz of the collision term. We also improve the earlier coherent quasiparticle approximation (cQPA) by giving a straightforward derivation of the spectral ansatz, a new way of organizing the gradient expansion, and a transparent way to derive the coherence-gradient resummed collision term. In both methods the transport equations can describe flavor coherence and particle–antiparticle coherence, and the related oscillations, of the mixing fermions.
In addition to formulating the local equations we apply them to baryogenesis in the early universe. More specifically, we study the details of CP-asymmetry generation in resonant leptogenesis and the evolution of the axial vector current in electroweak baryogenesis (in a time-dependent analogue). We solve the equations numerically, and perform extensive analysis and compare the results to semiclassical (Boltzmann) equations. The results cover known semiclassical effects. We find that dynamical treatment of local quantum coherence is necessary for an accurate description of CP-asymmetry generation. When these details are known they can then be partially incorporated into simpler (e.g. semiclassical) approaches. However, coherent quantum kinetic equations are needed for accurate results across different scenarios or wide parameter ranges.

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H. Jukkala
Wed, 23 Nov 22
48/71

Comments: PhD thesis (the compilation part); 103 pages, 7 figures. For the full thesis, see this https URL

Non-perturbative massless minimal quantum scalar field with $V(φ)=λφ^4/4!+βφ^3/3!$ in the inflationary de Sitter spacetime [CL]

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http://arxiv.org/abs/2211.12027


We consider a massless, minimally coupled quantum scalar field theory with an asymmetric self interaction, $V (\phi) = \lambda\phi^4/4!+\beta\phi^3/3!$ ($\lambda >0$) in the inflationary de Sitter spacetime. This potential is bounded from below. While the $\beta=0$ case has been much well studied, the motivation behind taking such a hybrid potential corresponds to the fact that it might generate finite negative vacuum expectation values of $V(\phi)$ as well of $\phi$, leading to some dynamical screening of the inflationary cosmological constant, $\Lambda$, at late times, with the initial conditions, $\langle \phi \rangle=0=\langle V(\phi) \rangle $. In this work we first compute the vacuum expectation values of $\phi,\, \phi^2$ and $V(\phi)$, using the late time, non-perturbative stochastic formalism. The backreactions to the inflationary $\Lambda$ are estimated. We also compute the dynamically generated mass of the scalar field using $\langle \phi^2 \rangle$. We next compute $\langle\phi^2\rangle$ using quantum field theory with respect to the initial Bunch-Davies vacuum at one and two loop, using the Schwinger-Keldysh formalism. These results show non-perturbative secular logarithms, growing with the cosmological time. Using next a recently proposed renormalisation group inspired formalism, we attempt to find out a resummed $\langle\phi^2\rangle$. We have been able to resum some part of the same which contains contributions only from the local self energy. The corresponding dynamically generated mass is computed. Comparison of the stochastic and the quantum field theory results shows that they differ numerically, although they have similar qualitative behaviour. Possible reasons for such quantitative mismatch is discussed. The manifestation of strong non-classical effects in the results found via both the formalisms has been emphasised.

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S. Bhattacharya and N. Joshi
Wed, 23 Nov 22
61/71

Comments: v1, 35pp, 10 figures, 1 table

Are nonsingular black holes with super-Planckian hair ruled out by S2 star data? [CL]

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http://arxiv.org/abs/2211.11585


We propose a novel nonsingular black-hole spacetime representing a strong deformation of the Schwarzschild solution with mass $M$ by an additional hair $\ell$, which may be hierarchically larger than the Planck scale. Our black-hole model presents a de Sitter core and $\mathcal{O}(\ell^2/r^2)$ slow-decaying corrections to the Schwarzschild solution. Our black-hole solutions are thermodynamically preferred when $0.2 \lesssim \ell/GM \lesssim \, 0.3$ and are characterized by strong deviations in the orbits of test particles from the Schwarzschild case. In particular, we find corrections to the perihelion precession angle scaling linearly with $\ell$. We test our model using the available data for the orbits of the S2 star around $\text{SgrA}^*$. These data strongly constrain the value of the hair $\ell$, casting an upper bound on it of $\sim \, 0.47 \, GM$, but do not rule out the possible existence of regular black holes with super-Planckian hair.

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M. Cadoni, M. Laurentis, I. Martino, et. al.
Tue, 22 Nov 22
13/83

Comments: 6 pages, 2 figures, 1 table