Tag Archives: High Energy Physics – Theory

The comoving curvature perturbation in Jordan and Einstein frames [CL]

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http://arxiv.org/abs/2305.15326


In the context of $F(\phi)R$ models of gravity, the conformal invariance of the curvature perturbation on the uniform-field slicings has been already demonstrated in several publications. In this work, we study the conformal invariance of the curvature perturbation defined on hypersurfaces that are comoving with an effective fluid. We derive the comoving curvature perturbation in each conformal frame and relate both. It is shown that the conformal invariance of this gauge-invariant curvature perturbation does not always hold, and the analysis on superhorizon and subhorizon scales is performed in the slow-roll regime of inflation. We find that the comoving curvature perturbation is conformally invariant on superhorizon scales but the same cannot be concluded on the subhorizon regime.

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J. Díaz and M. Karčiauskas
Thu, 25 May 23
64/64

Comments: 21 pages

Dark Sectors with Mass Thresholds Face Cosmological Datasets [CEA]

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http://arxiv.org/abs/2305.14166


Interacting dark sectors may undergo changes in the number of their relativistic species during the early universe, due to a mass threshold $m$ (similar to changes in the Standard Model bath), and in doing so affect the cosmic history. When such changes occur close to recombination, i.e., for $m\sim (0.1-10)~\text{eV}$, the stringent bound on the effective number of neutrino species, $N_{\text{eff}}$, can be relaxed and the value of the Hubble expansion rate $H_0$ inferred from Cosmic Microwave Background (CMB) observations raised. We search for such sectors (with and without mass thresholds) in the latest cosmological datasets, including the full-shape (FS) of BOSS DR12 galaxy power spectrum. We perform a detailed analysis, accounting for the choice of prior boundaries and additionally exploring the possible effects of dark sector interactions with (a fraction of) the dark matter. We find $\Delta N_{\text{eff}}\leq 0.55\, (0.46)$ at 95% C.L. with (without) a mass threshold. While a significantly larger Hubble rate is achieved in this scenario, $H_0=69.01^{+0.66}_{-1.1}$, the overall fit to CMB+FS data does not provide a compelling advantage over the $\Lambda$CDM model. Furthermore, we find that dark matter interactions with the dark sector do not significantly improve the (matter fluctuations) $S_8$ tension with respect to the $\Lambda$CDM model. Our work provides model-independent constraints on (decoupled) dark sectors with mass thresholds around the eV scale.

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I. Allali, F. Rompineve and M. Hertzberg
Wed, 24 May 23
81/81

Comments: 18 + 18 pages, 38 figures and tables

Minimal Preheating [CL]

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http://arxiv.org/abs/2305.11246


An oscillating inflaton field induces small amplitude oscillations of the Hubble parameter at the end of inflation. These Hubble parameter induced oscillations, in turn, trigger parametric particle production of all light fields, even if they are not directly coupled to the inflaton. We here study the induced particle production for a light scalar field (e.g. the Standard Model Higgs field) after inflation as a consequence of this effect. Our analysis yields a model-independent lower bound on the efficiency of energy transfer from the inflaton condensate to particle excitations.

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R. Brandenberger, V. Kamali and R. Ramos
Mon, 22 May 23
30/60

Comments: 9 pages, 7 figures

A generalization of photon sphere based on escape/capture cone [CL]

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http://arxiv.org/abs/2305.11208


In asymptotically flat spacetimes, bearing the null geodesics reaching the future null infinity in mind, we propose new concepts, the “dark horizons” as generalizations of the photon sphere. They are defined in terms of the structure of escape/capture cones of photons with respect to a unit timelike vector field. More specifically, considering a two-sphere that represents a set of emission directions of photons, the dark horizons are located at positions where a hemisphere is marginally included in the capture and escape cones, respectively. We show that both of them are absent in the Minkowski spacetime, while they exist in spacetimes with black hole(s) under a certain condition. We derive the general properties of the dark horizons in spherically symmetric spacetimes and explicitly calculate the locations of the dark horizons in the Vaidya spacetime and the Kerr spacetime.

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M. Amo, K. Izumi, H. Yoshino, et. al.
Mon, 22 May 23
38/60

Comments: 34 pages, 11figures

Leading Loops in Cosmological Correlators [CL]

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http://arxiv.org/abs/2305.11228


Cosmological correlators from inflation are often generated at tree level and hence loop contributions are bounded to be small corrections by perturbativity. Here we discuss a scenario where this is not the case. Recently, it has been shown that for any number of scalar fields of any mass, the parity-odd trispectrum of a massless scalar must vanish in the limit of exact scale invariance due to unitarity and the choice of initial state. By carefully handling UV-divergences, we show that the one-loop contribution is non-vanishing and hence leading. Surprisingly, the one-loop parity-odd trispectrum is simply a rational function of kinematics, which we compute explicitly in a series of models, including single-clock inflation. Although the loop contribution is the leading term in the parity-odd sector, its signal-to-noise ratio is typically bounded from above by that of a corresponding tree-level parity-even trispectrum, unless instrumental noise and systematics for the two observables differ. Furthermore, we identify a series of loop contributions to the wavefunction that cancel exactly when computing correlators, suggesting a more general phenomenon.

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M. Lee, C. McCulloch and E. Pajer
Mon, 22 May 23
42/60

Comments: 34 pages, 4 figures

A large $|η|$ approach to single field inflation [CL]

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http://arxiv.org/abs/2305.11568


Single field models of inflation capable to produce primordial black holes usually require a significant departure from the standard, perturbative slow-roll regime. In fact, in many of these scenarios, the size of the slow-roll parameter $|\eta|$ becomes larger than one during a short phase of inflationary evolution. In order to develop an analytical control on these systems, we explore the limit of $|\eta|$ large, and promote $1/|\eta|$ to a small quantity to be used for perturbative expansions. Formulas simplify, and we obtain analytic expressions for the two and three point functions of curvature fluctuations, which share some of the features found in realistic inflationary models generating primordial black holes. We study one-loop corrections in this framework: we discuss criteria for adsorbing ultraviolet divergences into the available parameters, leaving log-enhanced infrared contributions of controllable size.

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G. Tasinato
Mon, 22 May 23
54/60

Comments: 20 pages, 3 figures

Primordial black holes from null energy condition violation during inflation [CL]

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http://arxiv.org/abs/2305.10933


The violation of the null energy condition (NEC) is closely related to potential solutions for the cosmological singularity problem and may therefore play a crucial role in the very early universe. We explore a novel approach to generate primordial black holes (PBHs) via the violation of the NEC in a single-field inflationary scenario. In our scenario, the universe transitions from a first slow-roll inflation stage with a Hubble parameter H = Hinf1 to a second slow-roll inflation stage with H = Hinf2 > Hinf1, passing through an intermediate stage of NEC violation. The resulting primordial scalar power spectrum is naturally enhanced by the NEC violation at a certain wavelength. As a result, PBHs with masses and abundances of observational interest can be produced in our scenario. We also examine the phenomenological signatures of scalar-induced gravitational waves (SIGWs). Our work highlights the significance of utilizing a combination of PBHs, SIGWs, and primordial gravitational waves as a powerful probe for exploring the NEC violation during inflation.

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Y. Cai, M. Zhu and Y. Piao
Fri, 19 May 23
5/46

Comments: 8 pages, 5 figures

Relativistic drag forces on black holes from scalar dark matter clouds of all sizes [CL]

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http://arxiv.org/abs/2305.10492


We use numerical simulations of scalar field dark matter evolving on a moving black hole background to confirm the regime of validity of (semi-)analytic expressions derived from first principles for both dynamical friction and momentum accretion in the relativistic regime. We cover both small and large clouds (relative to the de Broglie wavelength of the scalars), and light and heavy particle masses (relative to the BH size). In the case of a small dark matter cloud, the effect of accretion is a non-negligible contribution to the total force on the black hole, even for small scalar masses. We confirm that this momentum accretion transitions between two regimes (wave- and particle-like) and we identify the mass of the scalar at which the transition between regimes occurs.

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D. Traykova, R. Vicente, K. Clough, et. al.
Fri, 19 May 23
27/46

Comments: 11 pages, 5 figures. Comments welcome!

Parameterized Parity Violation in Gravitational Wave Propagation [CL]

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http://arxiv.org/abs/2305.10478


Gravitational parity violation arises in a variety of theories beyond general relativity. Gravitational waves in such theories have their propagation altered, leading to birefringence effects in both the amplitude and speed of the wave. In this work, we introduce a generalized, theory-motivated parametrization scheme to study parity violation in gravitational wave propagation. This parametrization maps to parity-violating gravity theories in a straightforward way. We find that the amplitude and velocity birefringence effects scale with an effective distance measure that depends on how the dispersion relation is modified. Furthermore, we show that this generic parametrization can be mapped to the parametrized-post-Einsteinian (ppE) formalism with convenient applications to gravitational wave observations and model-agnostic tests of general relativity. We derive a mapping to the standard ppE waveform of the gravitational wave response function, and also find a ppE waveform mapping at the level of the polarization modes, $h_+$ and $h_\times$. Finally, we show how existing constraints in the literature translate to bounds on our new parity-violating parameters and discuss avenues for future analysis.

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L. Jenks, L. Choi, M. Lagos, et. al.
Fri, 19 May 23
31/46

Comments: 19 pages

Primordial Black Hole Reheating [CL]

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http://arxiv.org/abs/2305.10518


Post-inflationary reheating phase is usually said to be solely governed by the decay of coherently oscillating inflaton into radiation. In this submission, we explore a new avenue toward reheating through the evaporation of primordial black holes (PBHs). After the inflation, if PBHs form, depending on its initial mass, abundance, and inflaton coupling with the radiation, we found two physically distinct possibilities of reheating the universe. In one possibility, the thermal bath is solely obtained from the decay of PBHs while inflaton plays the role of dominant energy component in the entire process. In the other possibility, we found that PBHs itself dominate the total energy budget of the Universe during the course of evolution, and then its subsequent evaporation leads to radiation dominated universe. Furthermore, we analyze the impact of both monochromatic and extended PBH mass functions and estimate the detailed parameter ranges for which those distinct reheating histories are realized.

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M. Haque, E. Kpatcha, D. Maity, et. al.
Fri, 19 May 23
44/46

Comments: 17 pages, 9 figures

White dwarf cooling in $f(R,T)$ gravity [CL]

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http://arxiv.org/abs/2305.10144


In recent times, astounding observations of both over- and under-luminous type Ia supernovae have emerged. These peculiar observations hint not only at surpassing the Chandrasekhar limit but may also suggest potential modifications in the physical attributes of their progenitors, such as their cooling rate. This, in turn, can influence their temporal assessments and provide a compelling explanation for these intriguing observations. In this spirit, we investigate here the cooling process of white dwarfs in $f(R,T)$ gravity with the simplest model $f(R,T) = R + \lambda T$, where $\lambda$ is the model parameter. Our modelling suggests that the cooling timescale of white dwarfs exhibits an inverse relationship with the model parameter $\lambda$, which implies that for identical initial conditions, white dwarfs in $f(R,T)$ gravity cool faster. This further unveils that in the realm of $f(R,T)$ gravity, the energy release rate for white dwarfs increases as $\lambda$ increases. Furthermore, we also report that the luminosity of the white dwarfs also depends on $\lambda$ and an upswing in $\lambda$ leads to an amplification in the luminosity, and consequently a larger white dwarf in general relativity can exhibit comparable luminosity to a smaller white dwarf in $f(R,T)$ gravity.

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S. Bhattacharjee
Thu, 18 May 23
11/67

Comments: N/A

Frequency-domain approach to self-force in hyperbolic scattering [CL]

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http://arxiv.org/abs/2305.09724


We develop a frequency-domain method for calculating the self-force acting on a scalar charge on a fixed scattering geodesic in Schwarzschild spacetime. Existing frequency-domain methods, which are tailored for bound orbits, are inadequate here for several reasons. One must account for the continuous spectrum in the scattering problem, deal with slowly-convergent radial integrals that are hard to evaluate numerically, and confront the inapplicability of the standard self-force method of “extended homogeneous solutions”, which only works for compactly supported sources. We tackle each of these issues in turn, and then present a full numerical implementation, in which we calculate the self-force correction to the scatter angle due to scalar-field back-reaction. We perform a range of internal validation tests, as well as ones based on comparison with existing time-domain results. We discuss the merits and remaining limitations of our method, and outline directions for future work.

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C. Whittall and L. Barack
Thu, 18 May 23
31/67

Comments: 30 pages, 11 figures

Gravitational Positivity for Phenomenologists: Dark Gauge Boson in the Swampland [CL]

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http://arxiv.org/abs/2305.10058


The gravitational positivity bound gives quantitative “swampland” constraints on low-energy effective theories inside theories of quantum gravity. We give a comprehensive discussion of this bound for those interested in applications to phenomenological model building. We present a practical recipe for deriving the bound, and discuss subtleties relevant for realistic models. As an illustration, we study the positivity bound on the scattering of the massive gauge bosons in the Higgs/St\”{u}ckelberg mechanism. Under certain assumptions on gravitational amplitudes at high energy, we obtain a lower bound $m_{V} \gtrsim \Lambda_\mathrm{UV}^2 /g M_\mathrm{Pl}$ on the gauge boson mass $m_V$, where $g$ is the coupling constant of the gauge field, $M_\mathrm{Pl}$ is the reduced Planck mass and $\Lambda_\mathrm{UV}$ is the ultraviolet cutoff of the effective field theory. This bound can strongly constrain new physics models involving a massive gauge boson.

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K. Aoki, T. Noumi, R. Saito, et. al.
Thu, 18 May 23
38/67

Comments: 30 pages, 12 figures

Black holes that are too cold to respect cosmic censorship [CL]

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http://arxiv.org/abs/2305.08918


In this essay it is proved that there are black holes that are dangerously cold. In particular, by analyzing the emission spectra of highly charged black holes we reveal the fact that near-extremal black holes whose Bekenstein-Hawking temperatures lie in the regime $T_{\text{BH}}\lesssim m^6_e/e^3$ may turn into horizonless naked singularities, thus violating the cosmic censorship principle, if they emit a photon with the characteristic thermal energy $\omega=O(T_{\text{BH}})$ [here ${m_e,e}$ are respectively the proper mass and the electric charge of the electron, the lightest charged particle]. We therefore raise here the conjecture that, in the yet unknown quantum theory of gravity, the temperatures of well behaved black-hole spacetimes are fundamentally bounded from below by the relation $T_{\text{BH}}\gtrsim m^6_e/e^3$.

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S. Hod
Wed, 17 May 23
10/67

Comments: This essay is awarded 4th Prize in the 2023 Essay Competition of the Gravity Research Foundation. 8 pages

Unimodular Proca Theory: Breaking the U(1) gauge symmetry of unimodular gravity via a mass term [CL]

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http://arxiv.org/abs/2305.09380


We study the Hamiltonian structure of unimodular-like theories, where the cosmological constant (or other supposed constants of nature) are demoted from fixed parameters to classical constants of motion. No new local degrees of freedom are present as a result of a $U(1)$ gauge invariance of the theory. Hamiltonian analysis of the action reveals that the only possible gauge fixing that can be enforced is setting the spatial components of the four-volume time vector ${\cal T}^{i}\approx0$. As a consequence of this, the gauge-fixed unimodular path integral is equivalent to the minisuperspace unimodular path integral. However, should we break the $U(1)$ gauge invariance, two things happen: a massless propagating degree of freedom appears, and the (gauge-invariant) zero-mode receives modified dynamics. The implications are investigated, with the phenomenology depending crucially on the target “constant”.

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R. Isichei and J. Magueijo
Wed, 17 May 23
11/67

Comments: N/A

Quasinormal modes and grey-body factors of regular black holes with a scalar hair from the Effective Field Theory [CL]

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http://arxiv.org/abs/2305.09187


The Effective Field Theory (EFT) of perturbations on an arbitrary background geometry with a timelike scalar profile has been recently constructed in the context of scalar-tensor theories. Unlike General Relativity, the regular Hayward metric is realized as an exact background metric in the Effective Field Theory with timelike scalar profile without resorting to special matter field, such as nonlinear electrodynamics. The fundamental quasinormal mode for axial graviational perturbations of this black hole has been considered recently with the help of various methods. Here we make a further step in this direction and find that, unlike the fundamental mode, a few first overtones deviate from their Schwarzschild limit at a much higher rate. This outburst of overtones occurs because the overtones are extremely sensitive to the least change of the near-horizon geometry. The analytical formula for quasinormal modes is obtained in the eikonal regime. In addition, we calculated grey-body factors and showed that regular Hayward black hole with a scalar hair has smaller grey-body factor than the Schwarzschild one. Integration of the wave-like equation in time-domain shows that the power-law tails following the ring-down phase at late times are indistinguishable from the Schwarzschild ones.

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R. Konoplya
Wed, 17 May 23
32/67

Comments: 9 pages, revtex, 3 figures

Primordial black holes and inflation from double-well potentials [CEA]

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http://arxiv.org/abs/2305.09630


We investigate the formation of large peaks in the inflationary curvature power spectrum from double-well potentials. In such scenarios, the initial CMB spectrum is created at large field values. Subsequently, the inflaton will cross one of the minima and will decelerate rapidly as it reaches the local maximum at the origin, either falling back or crossing it. During this final phase, a significant peak in the curvature power spectrum can be generated. Our analysis reveals that this class of models produces more pronounced peaks than the more commonly studied quasi-inflection point scenarios with less tuning for the model parameters. Finally, we construct an explicit theoretically motivated inflationary scenario that is consistent with the latest CMB observations and capable of generating sufficiently large curvature perturbations for primordial black holes.

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A. Karam, N. Koivunen, E. Tomberg, et. al.
Wed, 17 May 23
44/67

Comments: 22 pages, 5 figures

Cold New Early Dark Energy pulls the trigger on the $H_0$ and $S_8$ tensions: a simultaneous solution to both tensions without new ingredients [CEA]

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http://arxiv.org/abs/2305.08895


In this work, we show that the Cold New Early Dark Energy (Cold NEDE) model in its original form can solve both the Hubble tension and the $S_8$ tension without adding any new ingredients at the fundamental level. So far, it was assumed that the trigger field in the Cold NEDE model is completely subdominant. However, relaxing this assumption and letting the trigger field contribute a mere $0.5\%$ of the total energy density leads to a resolution of the $S_8$ tension while simultaneously improving it as a solution to the $H_0$ tension. Fitting this model to baryonic acoustic oscillations, large-scale-structure, supernovae (including a SH0ES prior), and cosmic microwave background data, we report a preferred NEDE fraction of $f_\mathrm{NEDE}= 0.134^{+0.032}_{-0.025}$ ($68\%$ C.L.), lifting its Gaussian evidence for the first time above $5\sigma$ (up from $4 \sigma$ when the trigger contribution to dark matter is negligible). At the same time, we find the new concordance values $H_0 = 71.71 \pm 0.88 \,\mathrm{km}\, \mathrm{sec}^{-1}\, \mathrm{Mpc}^{-1}$ and $S_8 = 0.793 \pm 0.018$. Excluding large-scale structure data and the SH$_0$ES prior, both Gaussian tensions are reduced below the $2 \sigma$ level.

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J. Cruz, F. Niedermann and M. Sloth
Wed, 17 May 23
46/67

Comments: 40 pages, 7 figures, 8 tables

A short survey of matter-antimatter evolution in the primordial universe [CL]

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http://arxiv.org/abs/2305.09055


We offer a survey of the matter-antimatter evolution within the primordial Universe. While the origin of the tiny matter-antimatter asymmetry has remained one of the big questions in modern cosmology, antimatter itself has played a large role for much of the Universe’s early history. In our study of the evolution of the Universe we adopt the position of the standard model $\Lambda$-CDM Universe implementing the known baryonic asymmetry. We present the composition of the Universe across its temperature history while emphasizing the epochs where antimatter content is essential to our understanding. Special topics we address include the heavy quarks in quark-gluon plasma (QGP), the creation of matter from QGP, the free-streaming of the neutrinos, the vanishing of the muons, the magnetism in the electron-positron cosmos, and a better understanding of the environment of the Big Bang Nucleosynthesis (BBN) producing the light elements. We suggest but do not explore further that the methods used in exploring the early Universe may also provide new insights in the study of exotic stellar cores, magnetars, as well as gamma-ray burst (GRB) events. We describe future investigations required in pushing known physics to its extremes in the unique laboratory of the matter-antimatter early Universe.

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J. Rafelski, J. Birrell, A. Steinmetz, et. al.
Wed, 17 May 23
67/67

Comments: 46 pages, 26 figures

On the Decoherence of Primordial Gravitons [CL]

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http://arxiv.org/abs/2305.08071


It is well-known that the primordial scalar curvature and tensor perturbations, $\zeta$ and $\gamma_{ij}$, are conserved on super-horizon scales in minimal inflation models. However, their wave functional has a rapidly oscillating phase which is slow-roll unsuppressed, as can be seen either from boundary (total-derivative) terms of cosmological perturbations, or the WKB approximation of the Wheeler-DeWitt equation. Such an oscillatory phase involves gravitational non-linearity between scalar and tensor perturbations. By tracing out unobserved modes, the oscillatory phase causes faster decoherence of primordial gravitons compared to those by bulk interactions. Our results put a stronger lower bound of decoherence effect to the recent proposals probing squeezed primordial gravitons.

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S. Ning, C. Sou and Y. Wang
Tue, 16 May 23
2/83

Comments: 42 pages, 3 figures, 1 table

Dissipative Inflation via Scalar Production [CL]

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http://arxiv.org/abs/2305.07695


We describe a new mechanism that gives rise to dissipation during cosmic inflation. In the simplest implementation, the mechanism requires the presence of a massive scalar field with a softly-broken global $U(1)$ symmetry, along with the inflaton field. Particle production in this scenario takes place on parametrically sub-horizon scales, at variance with the case of dissipation into gauge fields. Consequently, the backreaction of the produced particles on the inflationary dynamics can be treated in a \textit{local} manner, allowing us to compute their effects analytically. We determine the parametric dependence of the power spectrum which deviates from the usual slow-roll expression. Non-Gaussianities are always sizeable whenever perturbations are generated by the noise induced by dissipation: $f_{\rm NL}^{\rm eq} \gtrsim {O}(10)$.

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P. Creminelli, S. Kumar, B. Salehian, et. al.
Tue, 16 May 23
6/83

Comments: 31 pages + appendices, 8 figures

Extinction biases quasar luminosity distances determined from quasar UV and X-ray flux measurements [GA]

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http://arxiv.org/abs/2305.08179


A sample of X-ray detected reverberation-mapped quasars provides a unique opportunity to compare cosmological constraints inferred using two well-established relations – the X-ray/UV luminosity ($L_{X}-L_{UV}$) relation and the broad-line region radius-UV monochromatic luminosity ($R-L$) relation. $L_{X}-L_{UV}$ and $R-L$ luminosity distances to the same quasars exhibit a distribution of their differences that is generally positively skewed for the six cosmological models we consider. This behaviour can be interpreted qualitatively to arise as a result of the dust extinction of UV/X-ray quasar emission. We show that the extinction always contributes to the non-zero difference between $L_{X}-L_{UV}$-based and $R-L$-based luminosity distances and we derive a linear relationship between the X-ray/UV colour index $E_{X-UV}$ and the median/mean value of the luminosity-distance difference, which also depends on the value of the $L_{X}-L_{UV}$ relation slope. Taking into account the prevailing positive values of the luminosity-distance difference median, we estimate an average X-ray/UV colour index of $\overline{E}{X-UV}=0.089 \pm 0.019$ mag, while the value based on the positive mean values of the difference is $\overline{E}{X-UV}=0.050\pm 0.013$ mag. We demonstrate that this amount of extinction is typical for the majority of quasars since it originates in the circumnuclear and interstellar media of host galaxies. It can only be slightly alleviated by the standard hard X-ray and far-UV extinction cuts used by Lusso et al. (2020). Consequently, the $L_{X}-L_{UV}$ relation QSO data compilation of Lusso et al. (2020) cannot be used for cosmological purposes.

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M. Zajaček, B. Czerny, N. Khadka, et. al.
Tue, 16 May 23
19/83

Comments: 12 pages, 7 figures, 3 tables; submitted to the MNRAS Main Journal, comments welcome

Measuring $H_0$ with Spectroscopic Surveys [CEA]

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http://arxiv.org/abs/2305.07977


Galaxy surveys map the three-dimensional distribution of matter in the Universe, encoding information about both the primordial cosmos and its subsequent evolution. By comparing the angular and physical scales of features in the galaxy distribution, we can compute the physical distance to the sample, and thus extract the Hubble parameter, $H_0$. In this chapter, we discuss how this is performed in practice, introducing two key standard rulers''. The first, the sound horizon at recombination, leads to baryon acoustic oscillations, and, by combining with external data from the CMB or Big Bang Nucleosynthesis, leads to a competitive $H_0$ constraint. Information can also be extracted from the physical scale of the horizon at matter-radiation equality; though somewhat less constraining, this depends on very different physics and is an important validation test of the physical model. We discuss how both such constraints can be derived (usingtemplate” and “full-shape” methodologies), and present a number of recent constraints from the literature, some of which are comparable in precision to (and independent from) Planck. Finally, we discuss future prospects for improving these constraints in the future.

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M. Ivanov and O. Philcox
Tue, 16 May 23
21/83

Comments: Invited chapter for the edited book “Hubble Constant Tension” (Eds. E. Di Valentino and D. Brout, Springer Singapore, expected in 2024)

Abelian-Higgs cosmic strings: effective action and particle radiation [CL]

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http://arxiv.org/abs/2305.08155


We utilized the duality between massive vector and massive Kalb-Ramond fields to derive an effective action for Abelian-Higgs cosmic strings. This enabled us to determine the classically renormalized string tension and facilitate calculations for back-reaction effects. Additionally, we derived a comprehensive expression for the energy flux of radiation emitted by Abelian-Higgs cosmic strings. Applying this equation to a cuspless loop, we obtained that the loop lifetime is proportional to the square of the loop length, which is in agreement with field-theory simulations.

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I. Rybak
Tue, 16 May 23
77/83

Comments: 14 pages, 1 figure

First-order phase transitions in Yang-Mills theories and the density of state method [CL]

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http://arxiv.org/abs/2305.07463


When studied at finite temperature, Yang-Mills theories in $3+1$ dimensions display the presence of confinement/deconfinement phase transitions, which are known to be of first order — the $SU(2)$ gauge theory being the exception. Theoretical as well as phenomenological considerations indicate that it is essential to establish a precise characterisation of these physical systems in proximity of such phase transitions. We present and test a new method to study the critical region of parameter space in non-Abelian quantum field theories on the lattice, based upon the Logarithmic Linear Relaxation (LLR) algorithm. We apply this method to the $SU(3)$ Yang Mills lattice gauge theory, and perform extensive calculations with one fixed choice of lattice size. We identify the critical temperature, and measure interesting physical quantities near the transition. Among them, we determine the free energy of the model in the critical region, exposing for the first time its multi-valued nature with a numerical calculation from first principles, providing this novel evidence in support of a first order phase transition. This study sets the stage for future high precision measurements, by demonstrating the potential of the method.

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B. Lucini, D. Mason, M. Piai, et. al.
Mon, 15 May 23
48/53

Comments: 25 pages, 21 figures

A robust explanation of CMB anomalies with a new formulation of inflationary quantum fluctuations [CL]

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http://arxiv.org/abs/2305.06057


The presence of CMB Hemispherical Asymmetry (HPA) challenges the current understanding of inflationary cosmology which does not generically predict the parity violation in the primordial correlations. In this paper, we shall review the recently proposed resolution to this based on a new formulation of quantizing inflationary fluctuations by focusing on the discrete spacetime transformations in a gravitational context. The predictive power of this formulation is that one can generate a scale dependent HPA in the context of single field inflation for all the primordial modes including scalar and tensor fluctuations without introducing any additional parameters. This result can be seen as an indication of spontaneous breaking of $\mathcal{C}\mathcal{P}\mathcal{T}$ symmetry in an expanding Universe, if confirmed by future observations it would be a great leap in the subject of quantum field theory in curved spacetime.

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K. Kumar and J. Marto
Thu, 11 May 23
23/55

Comments: 13 pages, 2 figures, Based on the talk given at the workshop on “Tensions in Cosmology” in Corfu 2022. This manuscript is written for Proceedings of Science (PoS), Corfu 2022 and it is based on arXiv: 2209.03928 [gr-qc]

Extreme-mass-ratio inspirals into rotating boson stars: nonintegrability, chaos, and transient resonances [CL]

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http://arxiv.org/abs/2305.05691


General relativity predicts that black holes are described by the Kerr metric, which has integrable geodesics. This property is crucial to produce accurate waveforms from extreme-mass-ratio inspirals. Astrophysical environments, modifications of gravity and new fundamental fields may lead to nonintegrable geodesics, inducing chaotic effects. We study geodesics around self-interacting rotating boson stars and find robust evidence of nonintegrability and chaos. We identify islands of stability around resonant orbits, where the orbital radial and polar oscillation frequency ratios, known as rotation numbers, remain constant throughout the island. These islands are generically present both in the exterior and the interior of compact boson stars. A monotonicity change of rotation curves takes place as orbits travel from the exterior to the interior of the star. Therefore, configurations with neutron-star-like compactness can support degenerate resonant islands. This anomaly is reported here for the first time and it is not present in black holes. Such configurations can also support extremely prolonged resonant islands that span from the exterior to the interior of the star and are shielded by thick chaotic layers. We adiabatically evolve inspirals using approximated post-Newtonian fluxes and find time-dependent plateaus in the rotation curves which are associated with island-crossing orbits. Crossings of external islands give rise to typical gravitational-wave glitches found in non-Kerr objects. Furthermore, when an inspiral is traversing an internal island that is surrounded by a thick chaotic layer, a new type of simultaneous multifrequency glitch occurs that may be detectable with space interferometers such as LISA, and can serve as evidence of an extreme-mass-ratio inspiral around a supermassive boson star.

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K. Destounis, F. Angeloni, M. Vaglio, et. al.
Thu, 11 May 23
28/55

Comments: 22 pages, 17 figures, higher resolution plots available upon request

Starobinsky Inflation from String Theory? [CL]

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http://arxiv.org/abs/2305.05703


Starobinsky inflation is currently one of the best models concerning agreement with cosmological data. Despite this observational success, it is still lacking a robust embedding into a UV complete theory. Previous efforts to derive Starobinsky inflation from string theory have been based on the derivation of higher derivative curvature terms from the low-energy limit of ten-dimensional string theory. This approach is however known to fail due to the difficulty to tame the effect of contributions proportional to the Ricci scalar to a power larger than two. In this paper we investigate an alternative attempt which exploits instead the ubiquitous presence of scalar fields in string compactifications combined with the fact that Starobinsky inflation can be recast as Einstein gravity coupled to a scalar field with a precise potential and conformal coupling to matter fermions. We focus in particular on type IIB K\”ahler moduli since they have shown to lead to exponential potentials with a Starobinsky-like plateau. We consider three classes of moduli with a different topological origin: the volume modulus, bulk fibre moduli, and blow-up modes. The only modulus with the correct coupling to matter is the volume mode but its potential does not feature any plateau at large field values. Fibre moduli admit instead a potential very similar to Starobinsky inflation with a natural suppression of higher curvature corrections, but they cannot reproduce the correct conformal coupling to matter. Blow-up modes have both a wrong potential and a wrong coupling. Our analysis implies therefore that embedding Starobinsky inflation into string theory seems rather hard. Finally, it provides a detailed derivation of the coupling to matter of fibre moduli which could be used as a way to discriminate Starobinsky from fibre inflation.

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M. Brinkmann, M. Cicoli and P. Zito
Thu, 11 May 23
38/55

Comments: 24 pages, 4 figures

Reconstructing k-inflation from $n_s(N)$ and reheating constraints [CL]

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http://arxiv.org/abs/2305.05042


Inspired by the reconstruction scheme of the inflaton field potential $V(\phi)$ from the attractors$n_s(N)$, we investigate the viability of reconstruct the inflationary potential within the framework of k-inflation for a non-linear kinetic term $K(X)=k_{n+1}X^n$ through three expressions for the scalar spectral index $n_s(N)$, namely: (i) $n_s-1=-\frac{2}{N}$, (ii) $n_s-1=-\frac{p}{N}$, and (iii) $n_s-1=-\frac{\beta}{N^q}$. For each reconstructed potential, we determine the values of the parameter space which characterize it by requiring that it must reproduce the observable parameters from PLANCK 2018 and BICEP/Keck results. Furthermore, we analyze the reheating era by assuming a constant equation of state, in which we derive the relations between the reheating duration, the temperature at the end of reheating together with the reheating epoch, and the number of $e$-folds during inflation. In this sense, we unify the inflationary observables in order to narrow the parameter space of each model within the framework of the reconstruction in k-inflation.

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R. Herrera, M. Housset, C. Osses, et. al.
Wed, 10 May 23
3/65

Comments: 40 pages and 6 figures

Possible hints of decreasing dark energy from supernova data [CEA]

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http://arxiv.org/abs/2305.04946


The potential energy from a time-dependent scalar field provides a possible explanation for the observed cosmic acceleration. In this paper, we investigate how the redshift vs brightness data from the recent Pantheon+ survey of type Ia supernovae constrain the possible evolution of a single scalar field for the period of time (roughly half the age of the universe) over which supernova data are available. Taking a linear approximation to the potential, we find that models providing a good fit to the data typically have a decreasing potential energy at present (accounting for over 99% of the allowed parameter space) with a significant variation in scalar potential ($\langle {\rm Range}(V)/V_0 \rangle \approx 0.97$) over the period of time corresponding to the available data ($z < 2.3$). Including quadratic terms in the potential, the data can be fit well for a wide range of possible potentials including those with positive or negative $V_2$ of large magnitude, and models where the universe has already stopped accelerating. We describe a few degeneracies and approximate degeneracies in the model that help explain the somewhat surprising range of allowed potentials.

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M. Raamsdonk and C. Waddell
Wed, 10 May 23
18/65

Comments: N/A

Instability of scalarized compact objects in Einstein-scalar-Gauss-Bonnet theories [CL]

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http://arxiv.org/abs/2305.05185


We investigate the linear stability of scalarized black holes (BHs) and neutron stars (NSs) in the Einstein-scalar-Gauss-Bonnet (GB) theories against the odd- and even-parity perturbations including the higher multipole modes. We show that the angular propagation speeds in the even-parity perturbations in the $\ell \to \infty$ limit, with $\ell$ being the angular multipole moments, become imaginary and hence scalarized BH solutions suffer from the gradient instability. We show that such an instability appears irrespective of the structure of the higher-order terms in the GB coupling function and is caused purely due to the existence of the leading quadratic term and the boundary condition that the value of the scalar field vanishes at the spatial infinity.~This indicates that the gradient instability appears at the point in the mass-charge diagram where the scalarized branches bifurcate from the Schwarzschild branch. We also show that scalarized BH solutions realized in a nonlinear scalarization model also suffer from the gradient instability in the even-parity perturbations. Our result also suggests the gradient instability of the exterior solutions of the static and spherically-symmetric scalarized NS solutions induced by the same GB coupling functions.

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M. Minamitsuji and S. Mukohyama
Wed, 10 May 23
31/65

Comments: 14 pages

Exploring departures from Schwarzschild black hole geometry in $f(R)$ gravity [CL]

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http://arxiv.org/abs/2305.04695


Different astrophysical methods can be combined to detect possible deviations from General Relativity. In this work, we consider a class of $f(R)$ gravity models selected by the existence of Noether symmetries. In this framework, it is possible to determine a set of static and spherically symmetric black hole solutions, encompassing small departures from the Schwarzschild geometry. In particular, when gravity is the only dominating interaction, we exploit the ray-tracing technique to reconstruct the image of a black hole, the epicyclic frequencies, and the black hole shadow profile. Moreover, when matter dynamics is also affected by an electromagnetic radiation force, we take into account the general relativistic Poynting-Robertson effect. In light of the obtained results, the proposed strategy results to be robust and efficient: on the one hand, it allows to investigate gravity from strong to weak field regimes; on the other hand, it is capable of detecting small departures from General Relativity, depending on the current observational sensitivity.

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V. Falco, F. Bajardi, R. D’Agostino, et. al.
Tue, 9 May 23
1/88

Comments: 19 pages; 7 figures; 2 tables; accepted for publication on EPJ C

Breakdown of the Newton-Einstein Standard Gravity at Low Acceleration in Internal Dynamics of Wide Binary Stars [GA]

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http://arxiv.org/abs/2305.04613


A gravitational anomaly is found at weak gravitational acceleration $g_{\rm{N}} < 10^{-9}$ m s$^{-2}$ from analyses of the dynamics of wide binary stars selected from the Gaia EDR3 database that have accurate distances, proper motions, and reliably inferred stellar masses. Implicit high-order multiplicities are required and the multiplicity fraction is calibrated so that binary internal motions agree statistically with Newtonian dynamics at a high enough acceleration of $10^{-8}$ m s$^{-2}$. The observed sky-projected motions and separation are deprojected to the three-dimensional relative velocity $v$ and separation $r$ through a Monte Carlo method, and a statistical relation between the Newtonian acceleration $g_{\rm{N}} \equiv GM/r^2$ (where $M$ is the total mass of the binary system) and a kinematic acceleration $g \equiv v^2/r$ is compared with the corresponding relation predicted by Newtonian dynamics. The empirical acceleration relation at $< 10^{-9}$ m s$^{-2}$ systematically deviates from the Newtonian expectation. A gravitational anomaly parameter $\delta_{\rm{obs-newt}}$ between the observed acceleration at $g_{\rm{N}}$ and the Newtonian prediction is measured to be: $\delta_{\rm{obs-newt}}= 0.034\pm 0.007$ and $0.109\pm 0.013$ at $g_{\rm{N}}\approx10^{-8.91}$ and $10^{-10.15}$ m s$^{-2}$, from the main sample of 26,615 wide binaries within 200 pc. These two deviations in the same direction represent a $10\sigma$ significance. The deviation represents a direct evidence for the breakdown of standard gravity at weak acceleration. At $g_{\rm{N}}=10^{-10.15}$ m s$^{-2}$, the observed to Newton predicted acceleration ratio is $g_{\rm{obs}}/g_{\rm{pred}}=10^{\sqrt{2}\delta_{\rm{obs-newt}}}=1.43\pm 0.06$. This systematic deviation agrees with the boost factor that the AQUAL theory predicts for kinematic accelerations in circular orbits under the Galactic external field.

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K. Chae
Tue, 9 May 23
38/88

Comments: 31 pages, 28 figures, submitted to ApJ

Exploring the viability of pseudo Nambu-Goldstone boson as ultralight dark matter in a mass range relevant for strong gravity applications [CL]

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http://arxiv.org/abs/2305.03776


We study a simple extension of the Standard Model featuring a dark sector with an ultralight pseudo Nambu-Goldstone boson as dark matter candidate. We focus on the mass range $\mathcal{O}(10^{-20} – 10^{-10})$ eV, relevant for strong gravity applications, and explore its production and evolution in the early Universe. The model is formulated in such a way that dark matter does not couple directly to photons or other Standard Model particles avoiding some of the most stringent cosmological bounds related to axion-like particles. In this work, two different scenarios are considered depending on whether dark matter is produced in a pre-inflationary or post-inflationary regime. We also discuss the effect from emergent topological defects such as cosmic strings and domain walls, and estimate the spectrum of stochastic gravitational waves produced by their decay, enabling to test the model at current and future gravitational-wave experiments.

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A. Morais, V. Oliveira, A. Onofre, et. al.
Tue, 9 May 23
72/88

Comments: 22 pages, 5 figures

New Horizons in the Holographic Conformal Phase Transition [CL]

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http://arxiv.org/abs/2305.03773


We describe cosmological solutions of the holographic dilaton with the aim of exploring alternatives to the commonly studied thermal Randall-Sundrum phase transition. It is well known that the thermal transition is typically strongly first order, with the requirement of a perturbative 5D gravity theory obstructing completion of the transition. This thermal transition corresponds to nucleation of an infrared brane through the surface of an AdS-Schwarzschild horizon. The approach we study instead invokes an early epoch in which the cosmology is fully 5-dimensional, with highly relativistic brane motion, and with Rindler horizons obscuring the infrared brane at early times. Our approach corresponds, via AdS/CFT, to a non-equilibrium approach to the conformal phase transition. We comment on a class of initial conditions that generically leads to completion of the phase transition without sacrificing perturbativity of the 5D theory.

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C. Eröncel, J. Hubisz, S. Lee, et. al.
Tue, 9 May 23
82/88

Comments: 43 pages, 9 figures

One loop to rule them all: Perturbativity in the presence of ultra slow-roll dynamics [CEA]

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http://arxiv.org/abs/2305.03491


We discuss the issue of perturbativity in single-field inflationary models with a phase of ultra slow-roll (USR) tailor suited to generate an order-one abundance of primordial black holes (PBHs). More in detail, we impose the condition that loop corrections made up of short-wavelength modes enhanced by the USR dynamics do not alter the tree-level power spectrum of curvature perturbations. In our analysis, the USR phase is preceded and followed by two stages of ordinary slow-roll (SR), and we model the resulting SR/USR/SR dynamics using both instantaneous and smooth transitions. Focusing on scales relevant for CMB observations, we find that it is not possible, with these arguments, to rule out the scenario of PBH formation via USR, not even in the limit of instantaneous transition. However, we also find that loop corrections of short modes on the power spectrum of long modes, even though not large enough to violate perturbativity requirements, remain appreciable and, most importantly, are not tamed in realistic realisations of smooth SR/USR/SR transitions. This makes perturbativity a powerful theoretical tool to constrain USR dynamics. We extend the analysis at any scale beyond those relevant for CMB observations. We find that loop corrections of short modes remain within the few percent if compared to the tree-level power spectrum. However, we also find one notable exception of phenomenological relevance: we show that the so-called dip in the power spectrum of curvature perturbation is an artifact of the tree-level computation.

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G. Franciolini, A. Iovino, M. Taoso, et. al.
Mon, 8 May 23
14/63

Comments: 31 pages, 12 figures

Dissipative Genesis of the Inflationary Universe [CL]

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http://arxiv.org/abs/2305.02366


We study an inflation model with a flat scalar potential supported by observations and find that slow-roll inflation can emerge after a quasi-cyclic phase of the Universe, where it undergoes repeated expansions and contractions for a finite time period. The initial conditions and the positive spatial curvature required for such nontrivial dynamics align with the quantum creation of the Universe. The key ingredients that trigger inflation are dissipative interactions of the inflaton, which are necessary to reheat the Universe after inflation and thus give us an observational handle on pre-inflationary physics. Our discovery implies that inflation occurs more robustly after the creation.

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H. Matsui, A. Papageorgiou, F. Takahashi, et. al.
Fri, 5 May 23
8/67

Comments: 5 pages, 1 figure

Dissipative Emergence of Inflation from Quasi-Cyclic Universe [CL]

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http://arxiv.org/abs/2305.02367


Inflationary models, especially those with plateau-type potentials, are consistent with the cosmological data, but inflation itself does not resolve the initial singularity. This singularity is resolved, for example, by the idea of the quantum creation of the Universe from nothing such as the tunneling and no-boundary proposals. The simplest one predicts a closed Universe. Motivated by these facts, we investigate the classical dynamics of a closed Universe with a plateau-type potential. Depending on the initial inflaton field value, the Universe can undergo a variety of events: an immediate Big Crunch, a bounce or cyclic phase, and inflation. Although the non-inflationary solutions may appear irrelevant to our Universe, they can be turned into a single or multiple bounces followed by inflation, taking into account the interactions necessary for the reheating of the Universe after inflation. Thus, the dissipative mechanism in our setup explains both the graceful entry to and exit from inflation and gives us an indirect observational handle on the Universe just after creation. We also comment on the implications of these solutions on the probabilistic interpretations of the wave function of the Universe.

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H. Matsui, A. Papageorgiou, F. Takahashi, et. al.
Fri, 5 May 23
49/67

Comments: 53 pages, 11 figures

de Sitter Space Decay and Cosmological Constant Relaxation in Braney Unimodular Gravity [CL]

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http://arxiv.org/abs/2305.02349


General covariant unimodular gravity frameworks, based on the Henneaux-Teitelboim formulation, are, in disguise, precisely $4$-form field theories corrected with higher dimension operators. In the presence of charged tensional membranes, any de Sitter space in all such theories is unstable and decays. If the fluxes sourced by membranes are mutually incommensurate, de Sitter geometries comprise a very refined discretuum of states. Whenever the $4$-form sector is dominated by terms linear in flux the almost-Minkowski space is the unique long-time attractor. As a result, a tiny cosmological constant is natural in all such frameworks, without appealing to anthropic reasoning.

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N. Kaloper
Fri, 5 May 23
67/67

Comments: 28 pages, 5 figures

Lorentzian quantum cosmology with torsion [CL]

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http://arxiv.org/abs/2305.01690


We evaluate the Lorentzian gravitational path integral in the presence of non-vanishing torsion with the application of the Picard-Lefschetz theory for minisuperspaces corresponding to a number of phenomenological bouncing cosmological models as well as for the inflationary paradigm. It turns out that the semi-classical wave function derived from the saddle points of the path integral formalism coincides with the solutions of the Wheeler-DeWitt equation. Intriguingly, our analysis showed that the relative probability, derived using these semi-classical wave functions favors universes with smaller values of torsion. Moreover, we find that in the inflationary case, non-zero values of a certain parity-violating component of the torsion enhance the power in the large physical length scales, which can have important observational implications. On the other hand, in the case of bouncing models, the power spectrum is characterized by an initial region of growth, an intermediate oscillatory region, and then again a final region of growth. The shape of the power spectrum in the initial and intermediate regions is sensitive to the abundance of the bounce-enabling matter and torsion, along with the initial wave function of the universe, while the final size modifies the behavior of the power spectrum in the smaller length scales.

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V. Mondal and S. Chakraborty
Thu, 4 May 23
4/60

Comments: N/A

Asymptotic behavior of null geodesics near future null infinity IV: Null-access theorem for generic asymptotically flat spacetime [CL]

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http://arxiv.org/abs/2305.01767


In our previous papers [arXiv:2106.03150, arXiv:2110.10917, arXiv:2208.00822], we analyzed the asymptotic behavior of future directed null geodesics near future null infinity and then we showed a proposition on the accessibility of the null geodesics to future null infinity in a specific class of asymptotically flat spacetimes. In this paper, we adopt the retarded time of the Bondi coordinate as the parameter for the null geodesics and then see that one can relax the assumptions imposed in our previous studies. As a consequence, we obtain a new null-access theorem for generic asymptotically flat spacetimes.

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M. Amo, K. Izumi, Y. Tomikawa, et. al.
Thu, 4 May 23
17/60

Comments: 16 pages, no figures

The dark matter unitarity bound at NLO [CL]

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http://arxiv.org/abs/2305.01680


We reexamine the consequences of perturbative unitarity on dark matter freeze-out when both Sommerfeld enhancement and bound state formation affect dark matter annihilations. At leading order (LO) the annihilation cross-section is infrared dominated and the connection between the unitarity bound and the upper bound on the dark matter mass depends only on how the different partial waves are populated. We compute how this picture is modified at next-to-leading order (NLO) with the goal of assigning a reliable theory uncertainty to the freeze-out predictions. We explicitly compute NLO corrections in a simple model with abelian gauge interactions and provide an estimate of the theoretical uncertainty for the thermal masses of heavy electroweak $n$-plets. Along the way, we clarify the regularization and matching procedure necessary to deal with singular potentials in quantum mechanics with a calculable relativistic UV completion.

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S. Bottaro and D. Redigolo
Thu, 4 May 23
35/60

Comments: 8 pages + appendices, 5+2 figures

Test of the Second Postulate of Relativity from Gravitational Wave Observations [CL]

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http://arxiv.org/abs/2304.14820


The second postulate of special relativity states that the speed of light in vacuum is independent of the emitter’s motion. Though this claim has been verified in various experiments and observations involving electromagnetic radiation with very high accuracy, such a test for gravitational radiation still needs to be explored. We analyzed data from the LIGO and Virgo detectors to test this postulate for gravitational radiation within the ambit of \textit{emission models}, where the speed of gravitational waves emitted by a source moving with a velocity $v$ relative to a stationary observer is given by ${c’ = c + k\,v}$, where $k$ is a constant. We have estimated the upper bound on the 90\% credible interval over $k$ that parameterizes the deviation from the second postulate to be ${k \leq 8.3 \times {10}^{-18}}$ which is several orders of magnitude more stringent compared to previous bounds obtained from electromagnetic observations. The Bayes’ factor supports the second postulate, with very strong evidence that the data is consistent with the null hypothesis $k = 0$. This confirms that the speed of gravity is independent of the motion of the emitter, upholding the principle of relativity for gravitational interactions.

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R. Ghosh, S. Nair, L. Pathak, et. al.
Wed, 3 May 23
4/67

Comments: 7 pages, 3 figures

The average equation of state for the oscillating inflaton field of the simplest $α$-attractor E-model [CL]

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http://arxiv.org/abs/2305.01159


In this work, we calculate the average equation of state for the oscillating inflaton field of the simplest $\alpha$-attractor E-model. We show that the average equation of state can be solved analytically. We discover that when $\alpha$ is small, the average equation of state of the oscillating inflaton field approaches that of a cosmological constant. This is the phenomenon of oscillating inflation.

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C. Lin
Wed, 3 May 23
44/67

Comments: 9 pages, 3 figures

Cosmic acceleration in entropic cosmology [CL]

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http://arxiv.org/abs/2305.01607


In this paper we study the viability of an entropic cosmological model. The effects of entropic gravity are derived from a modified entropy-area relationship with a volumetric entropy term. This model describes a late time limit {cosmic acceleration}, whose origin is related to a volumetric term in the entropy. Moreover, we analyze the phenomenological implications of the entropic model using the Supernovae {\it Pantheon} compilation and the observational Hubble parameter data to find consistency with cosmological observations. Finally, we show the equivalence between the entropic model and a brane world cosmological model, by means of an effective geometrical construction.

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J. Chagoya, I. Díaz-Saldaña, J. López-Domínguez, et. al.
Wed, 3 May 23
52/67

Comments: 10 pages, 3 figures

Loop Corrections in Gravitational Wave Spectrum in Single Field Inflation [CEA]

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http://arxiv.org/abs/2305.01527


We study the one-loop corrections in power spectrum of long gravitational waves induced from small scale modes in the models of single field inflation undergoing a phase of ultra-slow-roll (USR). We show that the spectrum of long tensor perturbations are largely unaffected by the loop corrections from the short scalar modes. In particular, the spectrum of long tensor perturbations is insensitive to the sharpness of the transition from the USR phase to the final slow-roll phase. This is in contrast to the case of scalar power spectrum in which the loop corrections can be large for a sharp transition while it is slow-roll suppressed in a mild transition. We study the tensor-scalar-scalar bispectrum in the squeezed limit and demonstrate that the Maldacena consistency condition does hold.

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H. Firouzjahi
Wed, 3 May 23
54/67

Comments: 19 pages, 1 figure

Primordial black holes formation in a early matter dominated era from the pre-big bang scenario [CL]

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http://arxiv.org/abs/2305.01430


We discuss the production of primordial black holes in an early matter dominated era, which typically takes place in string inspired early universe cosmological models. In particular, we consider a pre-big bang scenario (extending previous results regarding formation in the radiation dominated era) where the enhancement of curvature perturbations is induced by a variation of the sound-speed parameter c_s during the string phase of high-curvature inflation. After imposing all relevant observational constraints, we find that the considered class of models is compatible with the production of a large amount of primordial black holes, in the mass range relevant to dark matter, only for a small range of the parameters space. On the other hand, we find that a huge production of light primordial black holes may occur both in such matter dominated era and in the radiation dominated one.

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C. P. and M. G
Wed, 3 May 23
64/67

Comments: 7 pages, 3 figures

Observable Gravitational Waves from Hyperkination in Palatini Gravity and Beyond [CL]

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http://arxiv.org/abs/2305.01399


We consider cosmology with an inflaton scalar field with an additional quartic kinetic term. Such a theory can be motivated by Palatini $R+R^2$ modified gravity. Assuming a runaway inflaton potential, we take the Universe to become dominated by the kinetic energy density of the scalar field after inflation. Initially, the leading kinetic term is quartic and we call the corresponding period hyperkination. Subsequently, the usual quadratic kinetic term takes over and we have regular kination, until reheating. We study, both analytically and numerically, the spectrum of primordial gravitational waves generated during inflation and re-entering the horizon during the subsequent eras. We demonstrate that the spectrum is flat for modes re-entering during radiation domination and hyperkination and linear in frequency for modes re-entering during kination: kinetic domination boosts the spectrum, but hyperkination truncates its peak. As a result, the effects of the kinetic period can be extended to observable frequencies without generating excessive gravitational waves, which could otherwise destabilise the process of Big Bang Nucleosynthesis. We show that there is ample parameter space for the primordial gravitational waves to be observable in the near future. If observed, the amplitude and `knee’ of the spectrum will provide valuable insights into the background theory.

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S. López, K. Dimopoulos, A. Karam, et. al.
Wed, 3 May 23
66/67

Comments: 40 pages, 7 figures

Observational constraints on power law Starobinsky inflation [CEA]

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http://arxiv.org/abs/2305.00682


In this work we revisit power law, $\frac{1}{M^2}R^\beta$, inflation to find the deviations from $R^2$ inflation allowed by current CMB and LSS observations. We compute the power spectra for scalar and tensor perturbations numerically and perform MCMC analysis to put constraints on parameters $M$ and $\beta$ from Planck-2018, BICEP3 and other LSS observations. We consider general reheating scenario and also vary the number of e-foldings during inflation, $N_{pivot}$, along with the other parameters. We find $\beta = 1.966^{+0.035}{-0.042}$, $M= \left(3.31^{+5}{-2}\right)\times 10^{-5}$ and $N_{pivot} = 41^{+10}_{-10}$ with $95\%\, C.\, L.$. This indicates that the current observations allow deviation from Starobinsky inflation. The scalar spectral index, $n_s$, and tensor-to-scalar ratio, $r$, derived from these parameters, are consistent with the Planck and BICEP3 observations.

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S. Saini and A. Nautiyal
Tue, 2 May 23
34/57

Comments: 13 pages, 5 figures

Starobinsky-Type B-L Higgs Inflation Leading Beyond MSSM [CL]

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http://arxiv.org/abs/2305.00523


Models of induced-gravity inflation are formulated within Supergravity employing as inflaton the Higgs field which leads to a spontaneous breaking of a U(1)_{B-L} symmetry at Mgut=2×10^16 GeV. We use a renormalizable superpotential, fixed by a U(1) R symmetry, and logarithmic or semi-logarithmic Kahler potentials with integer prefactors which exhibit a quadratic non-minimal coupling to gravity. We find inflationary solutions of Starobinsky type in accordance with the observations. The inflaton mass is predicted to be of the order of 10^13 GeV. The model can be nicely linked to MSSM offering an explanation of the magnitude of the mu parameter consistently with phenomenological data. Also it allows for baryogenesis via non-thermal leptogenesis, provided that the gravitino is heavier than about 10 TeV.

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C. Pallis
Tue, 2 May 23
42/57

Comments: Prepared for the Proceedings of the Corfu Summer Institute 2022 — Conference: C22-08-28. arXiv admin note: substantial text overlap with arXiv:1804.07038

The $EB$-correlation in Resolved Polarized Images: Connections to Astrophysics of Black Holes [GA]

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http://arxiv.org/abs/2305.00387


We present an in-depth analysis of a newly proposed correlation function in visibility space, between the $E$ and $B$ modes of the linear polarization, hereafter the $EB$-correlation, for a set of time-averaged GRMHD simulations compared with the phase map from different semi-analytic models as well as the Event Horizon Telescope (EHT) 2017 data for M87* source. We demonstrate that the phase map of the time-averaged $EB$-correlation contains novel information that might be linked to the BH spin, accretion state and the electron temperature. A detailed comparison with a semi-analytic approach with different azimuthal expansion modes shows that to recover the morphology of the real/imaginary part of the correlation function and its phase, we require higher orders of these azimuthal modes. To extract the phase features, we propose to use the Zernike polynomial reconstruction developing an empirical metric to break degeneracies between models with different BH spins that are qualitatively similar. We use a set of different geometrical ring models with various magnetic and velocity field morphologies and show that both the image space and visibility based $EB$-correlation morphologies in MAD simulations can be explained with simple fluid and magnetic field geometries as used in ring models. SANEs by contrast are harder to model, demonstrating that the simple fluid and magnetic field geometries of ring models are not sufficient to describe them owing to higher Faraday Rotation depths. A qualitative comparison with the EHT data demonstrates that some of the features in the phase of $EB$-correlation might be well explained by the current models for BH spins as well as electron temperatures, while others may require a larger theoretical surveys.

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R. Emami, S. Doeleman, M. Wielgus, et. al.
Tue, 2 May 23
46/57

Comments: 26 pages, 21 Figures

Constraining the quintessential \texorpdfstring{$α$}{a}-attractor inflation through dynamical horizon exit method [CL]

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http://arxiv.org/abs/2305.00230


In the present paper, we perform a sub-Planckian quantum mode analysis of linear cosmological perturbation in the inflaton field over a classical quasi de-Siter metric background by dynamical horizon exit (DHE) method. In this way, we probe the inflationary regime of a quintessential $\alpha$-attractor model by analysing the COBE/Planck normalized power spectra, spectral indices, tensor to scalar ratio, number of e-folds, running of the spectral index and inflationary Hubble parameter in $k$-space. We compare our results with ordinary $\alpha$-attractor $E$ and $T$ models and with that of Planck-2018 results. Our estimated values of $n_s$ and $r$ lie within $68\%$ CL with respect to Planck data for $k=0.001 – 0.009$ Mpc$^{-1}$ for all values of $\alpha$. The $\alpha$ values, obtained in our calculations satisfy various post inflationary constraints regarding preheating and reheating, reported in current literature. We observe that quintessence sets an upper bound of $\alpha=4.3$ and thereby restricts the model from becoming of the power law type, making it more efficacious than ordinary $\alpha$-attractors in explaining both inflation and dark energy. A striking observation in our analyses is that, unlike in our previous study, we find a continuous values of $\alpha$ within $\frac{1}{10}\leq \alpha\leq 4.3$ for the specified $k$ range. At the end, we have shown that the model parameters constrained in this work give a very small vacuum density $\sim 10^{-117}-10^{-115} M_P^4$ which is an essential criterion for current and future dark energy observations of the universe.

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A. Sarkar and B. Ghosh
Tue, 2 May 23
52/57

Comments: 46 pages, 20 figures, 2 tables

Multi-field inflation with large scalar fluctuations: non-Gaussianity and perturbativity [CEA]

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http://arxiv.org/abs/2304.14260


Recently multi-field inflation models that can produce large scalar fluctuations on small scales have drawn a lot of attention, primarily because they could lead to primordial black hole production and generation of large second-order gravitational waves. In this work, we focus on models where the scalar fields responsible for inflation live on a hyperbolic field space. In this case, geometrical destabilisation and non-geodesic motion are responsible for the peak in the scalar power spectrum. We present new results for scalar non-Gaussianity and discuss its dependence on the model’s parameters. On scales around the peak, we typically find that the non-Gaussianity is large and close to local in form. We validate our results by employing two different numerical techniques, utilising the transport approach, based on full cosmological perturbation theory, and the $\delta N$ formalism, based on the separate universe approximation. We discuss implications of our results for the perturbativity of the underlying theory, focusing in particular on versions of these models with potentially relevant phenomenology at interferometer scales.

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L. Iacconi and D. Mulryne
Fri, 28 Apr 23
10/68

Comments: 36 pages, 17 figures

Dynamics of axion-neutral pseudoscalar mixing [CL]

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http://arxiv.org/abs/2304.13884


Axions mix with neutral pions after the QCD phase transition through their common coupling to the radiation bath via a Chern-Simons term, as a consequence of the $U(1)$ anomaly. The non-equilibrium effective action that describes this mixing phenomenon is obtained to second order in the coupling of neutral pions and axions to photons. We show that a misaligned axion condensate induces a neutral pion condensate after the QCD phase transition. The dynamics of the pion condensate displays long and short time scales and decays on the longer time scale exhibiting a phenomenon akin to the “purification” in a Kaon beam. On the intermediate time scales the macroscopic pion condensate is proportional to a condensate of the abelian Chern-Simons term induced by the axion. We argue that the coupling to the common bath also induces kinetic mixing. We obtain the axion and pion populations, and these exhibit thermalization with the bath. The mutual coupling to the bath induces long-lived axion- neutral pion coherence independent of initial conditions. The framework of the effective action and many of the consequences are more broadly general and applicable to scalar or pseudoscalar particles mixing in a medium.

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S. Cao, W. Huang and D. Boyanovsky
Fri, 28 Apr 23
51/68

Comments: 35 pages, 2 figures. arXiv admin note: text overlap with arXiv:2209.07658

Perturbative Correction to the Average Expansion Rate of Spacetimes with Perfect Fluids [CL]

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http://arxiv.org/abs/2304.14187


This paper discusses the leading-order correction induced by cosmological perturbations on the average expansion rate of an expanding spacetime, containing one or many perfect fluids. The calculation is carried out up to the second order in the perturbations, and is kept as general as possible. In particular, no approximation such as a long-wavelength or a short-wavelength limit is invoked, and all three types of perturbations (scalar, vector, and tensor) are considered. First, the average value of the expansion rate is computed over a three-dimensional space-like surface where the total density of the fluids is constant. Then, a formula is derived relating that average value to the one over any other surface, on which a different scalar property of the fluids is constant. Moreover, the general formulas giving the correction to the average expansion rate are applied, in particular, to the case of a spacetime containing a single fluid with a constant equation of state. The sign and the effective equation of state of the corresponding back-reaction effect in the first Friedmann equation are examined.

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V. Comeau
Fri, 28 Apr 23
53/68

Comments: N/A

Boson Star Normal Modes [CEA]

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http://arxiv.org/abs/2304.13054


Boson stars are gravitationally bound objects that arise in ultralight dark matter models and form in the centers of galactic halos or axion miniclusters. We systematically study the excitations of a boson star, taking into account the mixing between positive and negative frequencies introduced by gravity. We show that the spectrum contains zero-energy modes in the monopole and dipole sectors resulting from spontaneous symmetry breaking by the boson star background. We analyze the general properties of the eigenmodes and derive their orthogonality and completeness conditions which have non-standard form due to the positive-negative frequency mixing. The eigenvalue problem is solved numerically for the first few energy levels in different multipole sectors and the results are compared to the solutions of the Schr\”odinger equation in fixed boson star gravitational potential. The two solutions differ significantly for the lowest modes, but get close for higher levels. We further confirm the normal mode spectrum in 3D wave simulations where we inject perturbations with different multipoles. As an application of the normal mode solutions, we compute the matrix element entering the evaporation rate of a boson star immersed in a hot axion gas. The computation combines the use of exact wavefunctions for the low-lying bound states and of the Schr\”odinger approximation for the high-energy excitations.

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J. Chan, S. Sibiryakov and W. Xue
Thu, 27 Apr 23
14/78

Comments: 33 pages, 21 figures

Bouncing and inflationary dynamics in quantum cosmology in the de Broglie-Bohm interpretation [CL]

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http://arxiv.org/abs/2304.13059


The quantum cosmology of the flat Friedmann-Lema{\^i}tre-Robertson-Walker Universe, filled with a scalar field, is considered in the de Broglie-Bohm (dBB) interpretation framework. A stiff-matter quantum bounce solution is obtained. The bouncing and subsequent pre-inflationary and inflationary dynamics are studied in details. We consider some representative primordial inflation models as examples, for which analytical expressions characterizing the dynamical quantities can be explicitly derived. The dependence of the inflationary dynamics on the quantum bounce parameters is then analyzed. The parameters emerging from our description are constrained by requiring the produced dynamics to be in accordance with some key cosmological quantities. The constraining conditions are also illustrated through regions of parameter space in terms of the bounce quantities.

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G. Vicente, R. Ramos and V. Magalhães
Thu, 27 Apr 23
27/78

Comments: 18 pages, 2 figures

Halo Formation from Yukawa Forces in the Very Early Universe [CEA]

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http://arxiv.org/abs/2304.13053


If long-range attractive forces exist and are stronger than gravity then cosmic halo formation can begin in the radiation-dominated era. We study a simple realization of this effect in a system where dark matter fermions have Yukawa interactions mediated by scalar particles, analogous to the Higgs boson in the standard model. We develop a self-consistent description of the system including exact background dynamics of the scalar field, and precise modelling of the fermion density fluctuations. For the latter, we provide accurate approximations for the linear growth as well as quantitative modelling of the nonlinear evolution using N-body simulations. We find that halo formation occurs exponentially fast and on scales substantially larger than simple estimates predict. The final fate of these halos remains uncertain, but could be annihilation, dark stars, primordial black holes, or even the existence of galaxy-sized halos at matter-radiation equality. More generally, our results demonstrate the importance of mapping scalar-mediated interactions onto structure formation outcomes and constraints for beyond the standard model theories.

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G. Domènech, D. Inman, A. Kusenko, et. al.
Thu, 27 Apr 23
36/78

Comments: 22 pages + references, 13 figures

Inflation Correlators at the One-Loop Order: Nonanalyticity, Factorization, Cutting Rule, and OPE [CL]

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http://arxiv.org/abs/2304.13295


Inflation correlators with one-loop massive exchange encode rich information about the dynamics of the massive loop particles. Their nonanalytic behavior in certain soft limits leads to characteristic oscillatory pattern, which is the leading signal of many particle models of cosmological collider physics. In this work, we investigate systematically such nonanalyticity for arbitrary one-particle-irreducible (1PI) one-loop correlators in various soft limits. With the partial Mellin-Barnes representation, we present and prove a factorization theorem and a cutting rule for arbitrary 1PI one-loop inflation correlators, which is reminiscent of the on-shell cutting rule for flat-space scattering amplitudes. We also show how to understand this factorization theorem from the viewpoint of operator product expansion on the future boundary. As an application of the one-loop factorization theorem, we derive new analytic and exact formulae for nonlocal cosmological collider signals for massive one-loop four-point inflation correlators of all possible 1PI topologies, including the bubble, the triangle, and the box graphs. Finally, we show how to push the computation of nonlocal signals to higher orders in the momentum ratio.

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Z. Qin and Z. Xianyu
Thu, 27 Apr 23
37/78

Comments: 60 pages

Inflaton phenomenology via reheating in the light of PGWs and latest BICEP/$Keck$ data [CEA]

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http://arxiv.org/abs/2304.13637


We are in the era of precision cosmology which offers us a unique opportunity to investigate beyond standard model physics. Towards this endeavor, inflaton is assumed to be a perfect new physics candidate. In this submission, we explore the phenomenological impact of the latest observation of PLANCK and BICEP/$Keck$ data on the physics of inflation. We particularly study three different models of inflation, namely $\alpha$-attractor E, T, and the minimal plateau model. We further consider two different post-inflationary reheating dynamics driven by inflaton decaying into Bosons and Fermions. Given the latest data in the inflationary $(n_s-r)$ plane, we derive detailed phenomenological constraints on different inflaton parameters and the associated physical quantities, such as inflationary e-folding number, $N_{ k}$, reheating temperatures $T_{\rm re}$. Apart from considering direct observational data, we further incorporate the bounds from primordial gravitational waves (PGWs) and different theoretical constraints. Rather than in the laboratory, our results illustrate the potential of present and future cosmological observations to look for new physics in the sky.

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A. Chakraborty, M. Haque, D. Maity, et. al.
Thu, 27 Apr 23
43/78

Comments: 17 pages, 8 tables and 10 figures

Bañados-Silk-West effect with finite forces near different types of horizons: general classification of scenarios [CL]

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http://arxiv.org/abs/2304.13087


If two particles move towards a black hole and collide in the vicinity of the horizon, under certain conditions their energy $E_{c.m.}$ in the center of mass frame can grow unbounded. This is the Ba\~{n}ados-Silk-West (BSW) effect. Usually, this effect is considered for extremal horizons and geodesic (or electrogedesic) trajectories. We study this effect in a more general context, when both geometric and dynamic factors are taken into account. We consider generic axially symmetric rotating black holes. The near-horizon behavior of metric coefficients is determined by three numbers $p,~q,$ $k$ that appear in the Taylor expansions for different types of a horizon$.$ This includes nonextremal, extremal and ultraextremal horizons. We also give general classification of possible trajectories that include so-called usual, subcritical, critical and ultracritical ones depending on the near-horizon behavior of the radial component of the four-velocity. We assume that particles move not freely but under the action of some unspecified force. We find when the finiteness of a force and the BSW effect are compatible with each other. The BSW effect implies that one of two particles has fine-tuned parameters. We show that such a particle always requires an infinite proper time for reaching the horizon. Otherwise, either a force becomes infinite or a horizon fails to be regular. This realizes the so-called principle of kinematic censorship that forbids literally infinite $E_{c.m.}$ in any act of collision. The obtained general results are illustrated for the Kerr-Newman-(anti-)de Sitter metric used as an example. The description of diversity of trajectories suggested in our work can be of use also in other contexts, beyond the BSW effect. In particular, we find the relation between a force and the type of a trajectory.

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H. H.V.Ovcharenko and O. O.B.Zaslavskii
Thu, 27 Apr 23
62/78

Comments: 38 pages, 2 figures

Stochastic gravitational-wave background at 3G detectors as a smoking gun for microscopic dark matter relics [CEA]

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http://arxiv.org/abs/2304.13576


Microscopic horizonless relics could form in the early universe either directly through gravitational collapse or as stable remnants of the Hawking evaporation of primordial black holes. In both cases they completely or partially evade cosmological constraints arising from Hawking evaporation and in certain mass ranges can explain the entirety of the dark matter. We systematically explore the stochastic gravitational-wave background associated with the formation of microscopic dark-matter relics in various scenarios, adopting an agnostic approach and discussing the limitations introduced by existing constraints, possible ways to circumvent the latter, and expected astrophysical foregrounds. Interestingly, this signal is at most marginally detectable with current interferometers but could be detectable by third-generations instruments such as the Einstein Telescope, strengthening their potential as discovery machines.

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G. Franciolini and P. Pani
Thu, 27 Apr 23
74/78

Comments: 11 pages, 4 figures

New exact solutions in multi-scalar field cosmology [CL]

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http://arxiv.org/abs/2304.12360


We use the method of the superpotential to derive exact solutions describing inflationary cosmologies in multi-field models. An example that describes a solution that interpolates between two de Sitter universes is described in detail.

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J. Russo
Wed, 26 Apr 23
43/62

Comments: 16 pages, 4 figures

Inflationary E-models revisited [CEA]

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http://arxiv.org/abs/2304.12558


The E-type $\alpha$-attractor models of single-field inflation were generalized further in order to accommodate production of primordial black holes (PBH) via adding a near-inflection point to the inflaton scalar potential at smaller scales, in good agreement with measurements of the cosmic microwave background (CMB) radiation. A minimal number of new parameters was used but their fine-tuning was maximized in order to increase possible masses of PBH formed during an ultra-slow-roll phase leading to a large enhancement of the power spectrum of scalar (curvature) perturbations by 6 or 7 orders of magnitude against the power spectrum of perturbations observed in CMB. It was found that extreme fine-tuning of the parameters in our models can lead to a formation of the Earth-size PBH with the masses of approximately $10^{27}$ g, still in agreement with CMB observations. Quantum corrections are known to lead to the perturbative upper bound on the amplitude of large scalar perturbations responsible for PBH production. The quantum (one-loop) corrections in our models were found to be suppressed by one order of magnitude for PBH with the masses of approximately $10^{19}$ g, which may form the whole dark matter in the Universe.

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D. Frolovsky and S. Ketov
Wed, 26 Apr 23
50/62

Comments: 12 pages, 7 figures, LaTeX

Adiabatic and isocurvature perturbations in extended theories with non–minimally coupled fields [CL]

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http://arxiv.org/abs/2304.12364


The scalar field sector in low–energy effective field theories motivated by string theory often contains several scalar fields, some of which possess non–standard kinetic terms. In this paper, we study theories with two scalar fields, in which one of the fields has a non–canonical kinetic term. The kinetic coupling is allowed to depend on both fields, going beyond the work in the literature, which usually considers the case of the coupling to depend on the other field only. Our aim is to study adiabatic and isocurvature perturbations in these extended theories. Our results show that the evolution equation for the curvature perturbation does not change when allowing the coupling to depend on both fields, while the effective mass of the entropy perturbation changes. We find expressions for the spectral index and its running at horizon crossing and at the end of inflation. We apply the formalism and study three phenomenological models, with different kinetic couplings.

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M. Angelis and C. Bruck
Wed, 26 Apr 23
58/62

Comments: 17 pages, 3 figures

Initial conditions problem in cosmological inflation revisited [CL]

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http://arxiv.org/abs/2304.12150


We present first results from a novel numerical relativity code based on a tetrad formulation of the Einstein-scalar field equations combined with recently introduced gauge/frame invariant diagnostics indicating that inflation does not solve the homogeneity and isotropy problem beginning from generic initial conditions following a big bang.

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D. Garfinkle, A. Ijjas and P. Steinhardt
Wed, 26 Apr 23
62/62

Comments: 10 pages, 4 figures

Gravitational-Wave Phasing of Compact Binary Systems to the Fourth-and-a-Half post-Newtonian Order [CL]

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http://arxiv.org/abs/2304.11185


The inspiral phase of gravitational waves emitted by spinless compact binary systems is derived through the fourth-and-a-half post-Newtonian (4.5PN) order beyond quadrupole radiation, and the leading amplitude mode ($\ell$, m) = (2, 2) is obtained at 4PN order. We also provide the radiated flux, as well as the phase in the stationary phase approximation. Rough numerical estimates for the contribution of each PN order are provided for typical systems observed by current and future gravitational wave detectors.

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L. Blanchet, G. Faye, Q. Henry, et. al.
Tue, 25 Apr 23
47/72

Comments: 9 pages, 1 table

The $π$-axion and $π$-axiverse of dark QCD [CL]

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http://arxiv.org/abs/2304.11176


Axions and axion-like particles (ALPs) are a prominent dark matter candidate, drawing motivation in part from the axiverse of string theory. Axion-like particles can also arise as composite degrees of freedom of a dark sector, for example, as dark pions in dark Quantum Chromo-Dynamics. In a dark Standard Model (SM) wherein all 6 quark flavors are light while the photon is massive, one finds a rich low-energy spectrum of stable and ultralight particles, in the form of neutral and charged dark scalars, and complex neutral scalars analogous to the SM kaon, with mass splittings determined by the mass and charge of the dark quarks. The model finds a natural portal to the visible sector via kinetic coupling of the dark and visible photons, and consequent millicharges for dark matter. The dark matter can be a mixture of all these ultralight bosonic degrees of freedom, and exhibit both parity-even and parity-odd interactions, making the theory testable at a wide variety of experiments. In context of dark QCD with $N_f$ flavors of light quarks, this scenario predicts $N_f^2-1$ ultralight axion-like particles — effectively an axiverse from dark QCD. This ‘$\pi$-axiverse’ is consistent with but makes no recourse to string theory, and is complementary to the conventional string theory axiverse.

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S. Alexander, H. Gilmer, T. Manton, et. al.
Tue, 25 Apr 23
56/72

Comments: N/A

Neutron star phase transition as the origin for the fast radio bursts and soft gamma-ray repeaters of SGR J1935+2154 [HEAP]

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http://arxiv.org/abs/2304.10871


Magnetars are believed as neutron stars (NSs) with strong magnetic fields. X-ray flares and fast radio bursts (FRBs) have been observed from the magnetar (soft gamma-ray repeater, SGR J1935+2154). We propose that the phase transition of the NS can power the FRBs and SGRs.Based on the equation of state provided by the MIT bag model and the mean field approximation, we solve the Tolman-Oppenheimer-Volkoff equations to get the NS structure. With spin-down of the NS, the hadronic shell gradually transfers to the quark shell.The gravitational potential energy released by one time of the phase transition can be achieved. The released energy, time interval between two successive phase transitions, and glitch are all consistent with the observations of the FRBs and the X-ray flares from SGR J1935+2154. We conclude that the phase transition of an NS is a plausible mechanism to power the SGRs as well as the repeating FRBs.

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J. Shen, Y. Zou, S. Yang, et. al.
Mon, 24 Apr 23
13/41

Comments: 11 pages, 3 figures

Synchronizing the Consistency Relation [CEA]

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http://arxiv.org/abs/2304.10559


We study the $N$-point function of the density contrast to quadratic order in the squeezed limit during the matter-dominated (MD) and radiation-dominated (RD) eras in synchronous gauge. Since synchronous gauge follows the free-fall frame of observers, the equivalence principle dictates that in the gradient approximation for the long-wavelength mode there is only a single, manifestly time-independent consistency relation for the $N$-point function. This simple form is dictated by the initial mapping between synchronous and local coordinates, unlike Newtonian gauge and its correspondingly separate dilation and Newtonian consistency relations. Dynamical effects only appear at quadratic order in the squeezed limit and are again characterized by a change in the local background, also known as the separate universe approach. We show that for the 3-point function the compatibility between these squeezed-limit relations and second-order perturbation theory requires both the initial and dynamical contributions to match, as they do in single-field inflation. This clarifies the role of evolution or late-time projection effects in establishing the consistency relation for observable bispectra, which is especially important for radiation acoustic oscillations and for establishing consistency below the matter-radiation equality scale in the MD era. Defining an appropriate angle and time average of these oscillations is also important for making separate universe predictions of spatially varying local observables during the RD era, which can be useful for a wider range of cosmological predictions beyond $N$-point functions.

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K. Inomata, H. Lee and W. Hu
Mon, 24 Apr 23
15/41

Comments: 65 pages, 1 figure

Gravitationally modulated quantum correlations: Discriminating classical and quantum models of ultra-compact objects with Bell nonlocality [CL]

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http://arxiv.org/abs/2304.10868


We investigate the relation between quantum nonlocality and gravity at the astrophysical scale, both in the classical and quantum regimes. Considering particle pairs orbiting in the strong gravitational field of ultra-compact objects, we find that the violation of Bell inequality acquires an angular modulation factor that strongly depends on the nature of the gravitational source. We show how such gravitationally-induced modulation of quantum nonlocality readily discriminates between black holes (both classical and inclusive of quantum corrections) and string fuzzballs, i.e., the true quantum description of ultra-compact objects according to string theory. These findings promote Bell nonlocality as a potentially key tool in comparing different models of classical and quantum gravity and putting them to the test.

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L. Petruzziello and F. Illuminati
Mon, 24 Apr 23
27/41

Comments: 12 pages, 4 figures

Disformal symmetry in the Universe: mimetic gravity and beyond [CL]

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http://arxiv.org/abs/2304.11035


Symmetries play an important role in fundamental physics. In gravity and field theories, particular attention has been paid to Weyl (or conformal) symmetry. However, once the theory contains a scalar field, conformal transformations of the metric can be considered a subclass of a more general type of transformation, so-called disformal transformation. Here, we investigate the implications of pure disformal symmetry in the Universe. We derive the form of general disformal invariant tensors from which we build the most general disformal invariant action. We argue that, in cosmology, disformal symmetry amounts to require that the lapse function is fully replaced by a (time-like) scalar field at the level of the action. We then show that disformal symmetry is in general an exactly equivalent formulation of general mimetic gravity. Lastly, we go beyond mimetic gravity and find that a particular class of invariance leads to seemingly Ostrogradski-like (with higher derivatives) Lagrangians, which are nevertheless absent of Ostrogradski ghosts in a cosmological background, despite having an additional degree of freedom. We also propose an application of our formalism to find new invertible disformal transformations, where the coefficient involves higher derivatives and curvature, further expanding the theory space of scalar-tensor theories.

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G. Domènech and A. Ganz
Mon, 24 Apr 23
33/41

Comments: 21 pages

Slow Contraction and the Weyl Curvature Hypothesis [CL]

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http://arxiv.org/abs/2304.10030


Using the power of numerical relativity, we show that, beginning from generic initial conditions that are far from flat, homogeneous and isotropic and have a large Weyl curvature, a period of slow contraction rapidly drives spacetime towards vanishingly small Weyl curvature as the total energy density grows, thus providing a dynamical mechanism that satisfies the Weyl Curvature Hypothesis. We also demonstrate a tight correlation between the Weyl Curvature Hypothesis and ultralocal behavior for canonical scalar fields with a sufficiently steep negative potential energy density.

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A. Ijjas
Mon, 24 Apr 23
34/41

Comments: 5 pages, 5 figures

Dai-Freed anomaly in the standard model and topological inflation [CL]

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http://arxiv.org/abs/2304.10100


When we impose the discrete symmetry in the standard model we have Dai-Freed global anomalies. However, interestingly if we introduce three right-handed neutrinos we can have an anomaly-free discrete $Z_4$ gauge symmetry. This $Z_4$ symmetry should be spontaneously broken down to the $Z_2$ symmetry to generate the heavy Majorana masses for the right-handed neutrinos. We show that this symmetry breaking naturally generates topological inflation, which is consistent with the CMB observations at present and predicts a significant tensor mode with scalar-tensor ratio $r > 0.03$. The right-handed neutrinos play an important role in reheating processes. The reheating temperature is as high as $\sim 10^8$GeV, and non-thermal leptogenesis successfully takes place.

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M. Kawasaki and T. Yanagida
Fri, 21 Apr 23
32/60

Comments: 9 pages and 2 figures

Clockwork Cosmology [CL]

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http://arxiv.org/abs/2304.09205


The higher order generalisation of the clockwork mechanism to gravitational interactions provides a means to generate an exponentially suppressed coupling to matter from a fundamental theory of multiple interacting gravitons, without introducing large hierarchies in the underlying potential and without the need for a dilaton, suggesting a possible application to the hierarchy problem. We work in the framework of ghost free multi-gravity with “nearest-neighbour” interactions, and present a formalism by which one is able to construct potentials such that the theory will always exhibit this clockwork effect. We also consider cosmological solutions to the general theory, where all metrics are of FRW form, with site-dependent scale factors/lapses. We demonstrate the existence of multiple deSitter vacua where all metrics share the same Hubble parameter, and we solve the modified Einstein equations numerically for an example clockwork model constructed using our formalism, finding that the evolution of the metric that matter couples to is essentially equivalent to that of general relativity at the modified Planck scale. It is important to stress that while we focus on the application to clockwork theories, our work is entirely general and facilitates finding cosmological solutions to any ghost free multi-gravity theory with “nearest-neighbour” interactions. Moreover, we clarify previous work on the continuum limit of the theory, which is generically a scalar-tensor braneworld, using the Randall-Sundrum model as a special case and showing how the discrete-clockwork cosmological results map to the continuum results in the appropriate limit.

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K. Wood, P. Saffin and A. Avgoustidis
Thu, 20 Apr 23
27/57

Comments: 48 pages, 4 figures

BCS in the Sky: Signatures of Inflationary Fermion Condensation [CL]

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http://arxiv.org/abs/2304.09428


We consider a Bardeen-Cooper-Schrieffer (BCS)-like model in the inflationary background. We show that with an axial chemical potential, the attractive quartic fermion self-interaction can lead to a BCS-like condensation. In the de Sitter (dS) limit of inflation, we perform the first computation of the non-perturbative effective potential that includes the full spacetime curvature effects in the presence of the chemical potential. The corresponding BCS phase transition is always first-order, when the varying Hubble is interpreted as an effective Gibbons-Hawking temperature of dS spacetime. In the condensate phase, the theory can be understood from UV and IR sides as fermionic and bosonic, respectively. This leads to distinctive signatures in the primordial non-Gaussianity of curvature perturbations. Namely, the oscillatory cosmological collider signal is smoothly turned off at a finite momentum ratio, since different momentum ratios effectively probe different energy scales. In addition, such BCS phase transitions can also source stochastic gravitational waves, feasible for future experiments.

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X. Tong, Y. Wang, C. Zhang, et. al.
Thu, 20 Apr 23
48/57

Comments: 30 pages, 8 figures

Gauge/frame invariant variables for the numerical relativity study of cosmological spacetimes [CL]

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http://arxiv.org/abs/2304.07616


To numerically evolve the full Einstein equations (or modifications thereof), simulations of cosmological spacetimes must rely on a particular formulation of the field equations combined with a specific gauge/frame choice. Yet truly physical results cannot depend on the given formulation or gauge/frame choice. In this paper, we present a resolution of the gauge problem and, as an example, numerically implement it to evaluate our previous work on contracting spacetimes.

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A. Ijjas
Wed, 19 Apr 23
14/58

Comments: 22 pages, 8 figures

Exorcising the Ghost Condensate Dark Energy with a Sextic Dispersion Relation [CL]

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http://arxiv.org/abs/2304.07344


The universe’s current acceleration is a pretty recent phenomenon in cosmological time scales. This means that the modes that have left our horizon since the beginning of the contemporary acceleration phase, have not really reached the exact IR limit. Noting this observation, we reconsider the possibility of having a ghost condensate as dark energy with a sixth-order dispersion relation. Looking at the three-point function of such a theory, we obtain the constraints on the coefficient of the sixth-order dispersion relation to avoid strong coupling. Such a ghost condensate if coupled to the standard model fields, induces a constant Lorentz-violating spin-dependent force, which can gravitate or anti-gravitate.

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A. Ashoorioon and A. Yousefi-Sostani
Wed, 19 Apr 23
25/58

Comments: 15+1 pages

Effective description of generalized disformal theories [CL]

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http://arxiv.org/abs/2304.08624


Generalized disformal transformations enable us to construct the generalized disformal Horndeski theories, which form the most general class of ghost-free scalar-tensor theories to this date. We extend the effective field theory (EFT) of cosmological perturbations to incorporate these generalized disformal Horndeski theories. The main difference from the conventional EFT is that our extended EFT involves operators with higher spatial derivatives of the lapse function. Our EFT also accommodates the generalized disformal transformation of U-DHOST theories.

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K. Takahashi, M. Minamitsuji and H. Motohashi
Wed, 19 Apr 23
26/58

Comments: 14 pages

Primordial Black Holes and Loops in Single-Field Inflation [CEA]

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http://arxiv.org/abs/2304.07801


Using the $\delta N$ formalism we calculate the one-loop correction to the large-scale power spectrum of the curvature perturbation in the standard scenario where primordial black holes are formed in the early universe thanks to a phase of ultra-slow-roll in single-field inflation. We explicitly show that one-loop corrections are negligible when the transition from the ultra-slow-roll to the slow-roll phase is smooth. We conclude that the PBH formation scenario through a ultra-slow-roll phase is viable.

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H. Firouzjahi and A. Riotto
Tue, 18 Apr 23
50/80

Comments: 11 pages

Parity violating scalar-tensor model in teleparallel gravity and its cosmological application [CL]

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http://arxiv.org/abs/2304.07138


The parity violating model based on teleparallel gravity is a competitive scheme for parity violating gravity, which has been preliminary studied in the literature. To further investigate the parity violating model in teleparallel gravity, in this paper, we construct all independent parity-odd terms that are quadratic in torsion tensor and coupled to a scalar field in a way without higher-order derivatives. Using these parity-odd terms, we formulate a general parity violating scalar-tensor model in teleparallel gravity and obtain its equations of motion. To explore potentially viable models within the general model, we investigate the cosmological application of a submodel of the general model in which terms above the second power of torsion are eliminated. We focus on analyzing cosmological perturbations and identify the conditions that preserve the parity violating signal of gravitational waves at linear order while avoiding the ghost instability.

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H. Rao and D. Zhao
Mon, 17 Apr 23
33/51

Comments: 17 pages. arXiv admin note: text overlap with arXiv:2201.02357, arXiv:2301.02847

Early Structure Formation from Cosmic String Loops in Light of Early JWST Observations [CEA]

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http://arxiv.org/abs/2304.06429


Cosmic strings, if they exist, source nonlinear and non-Gaussian perturbations all the way back to the time of equal matter and radiation (and earlier). Here, we compute the mass function of halos seeded by a scaling distribution of cosmic string loops, and we compare the results with the predictions of the standard Gaussian $\Lambda$CDM model. Assuming a simple linear relation between stellar mass and halo mass, we also compute the stellar mass function. The contribution of cosmic strings dominates at sufficiently high redshifts $z > z_c$ where $z_c$ depends on the mass of the halo and on the mass per unit length $\mu$ of the strings and is of the order $z_c \sim 12$ for $G\mu = 10^{-8}$. We find that strings with this value of $G\mu$ can explain the preliminary JWST data on the high redshift stellar mass density. Based on an extreme value statistic, we find that the mass of the heaviest expected string-seeded galaxy for the current JWST sky coverage is compatible with the heaviest detected galaxy. Given the uncertainties in the interpretation of the JWST data, we discuss predictions for higher redshift observations.

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H. Jiao, R. Brandenberger and A. Refregier
Fri, 14 Apr 23
7/64

Comments: 13 pages, 8 figures

Universal Gravitational Wave Signatures of Cosmological Solitons [CEA]

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http://arxiv.org/abs/2304.06709


Cosmological solitonic objects such as monopoles, cosmic strings, domain walls, oscillons and Q-balls often appear in theories of the early Universe. We demonstrate that such scenarios are generically accompanied by a novel production source of gravitational waves stemming from soliton isocurvature perturbations. The resulting induced universal gravitational waves (UGWs) reside at lower frequencies compared to gravitational waves typically associated with soliton formation. We show that UGWs from axion-like particle (ALP) oscillons, originating from ALP misalignment, extend the frequency range of produced gravitational waves by more than two orders of magnitude regardless of the ALP mass and decay constant and can be observable in upcoming gravitational wave experiments. UGWs open a new route for gravitational wave signatures in broad classes of cosmological theories.

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K. Lozanov, M. Sasaki and V. Takhistov
Fri, 14 Apr 23
29/64

Comments: 8 pages, 2 figures

Exploring Mirror Twin Higgs Cosmology with Present and Future Weak Lensing Surveys [CEA]

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http://arxiv.org/abs/2304.06308


We explore the potential of precision cosmological data to study non-minimal dark sectors by updating the cosmological constraint on the mirror twin Higgs model (MTH). The MTH model addresses the Higgs little hierarchy problem by introducing dark sector particles. In this work, we perform a Bayesian global analysis that includes the latest cosmic shear measurement from the DES three-year survey and the Planck CMB and BAO data. In the early Universe, the mirror baryon and mirror radiation behave as dark matter and dark radiation, and their presence modifies the Universe’s expansion history. Additionally, the scattering between mirror baryon and photon generates the dark acoustic oscillation process, suppressing the matter power spectrum from the cosmic shear measurement. We demonstrate how current data constrain these corrections to the $\Lambda$CDM cosmology and find that for a viable solution to the little hierarchy problem, the proportion of MTH dark matter cannot exceed about $30\%$ of the total dark matter density, unless the temperature of twin photon is less than $30\%$ of that of the standard model photon. While the MTH model is presently not a superior solution to the observed $H_0$ tension compared to the $\Lambda$CDM+$\Delta N_{\rm eff}$ model, we demonstrate that it has the potential to alleviate both the $H_0$ and $S_8$ tensions, especially if the $S_8$ tension persists in the future and approaches the result reported by the Planck SZ (2013) analysis. In this case, the MTH model can relax the tensions while satisfying the DES power spectrum constraint up to $k \lesssim 10~h\rm {Mpc}^{-1}$. If the MTH model is indeed accountable for the $S_8$ and $H_0$ tensions, we show that the future China Space Station Telescope (CSST) can determine the twin baryon abundance with a $10\%$ level precision.

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L. Zu, C. Zhang, H. Chen, et. al.
Fri, 14 Apr 23
48/64

Comments: 32 pages, 12 figures, 4 tables

Multi-brane cosmology [CL]

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http://arxiv.org/abs/2304.05586


5D warped extra dimension models with multiple 3-branes can naturally realize multiple hierarchical mass scales which are ubiquitous in physics beyond the Standard Model. We discuss cosmological consequences of such multi-brane models with stabilized radions. It is confirmed that for temperatures below the scale of the IR brane at the end of the extra dimension, we recover the ordinary expansion of the Universe, with the Hubble expansion rate determined by sum of the physical energy densities on all 3-branes where they are localized. In addition, we explore the cosmology for temperatures above the scales of the intermediate and IR branes where the Universe is described by a spacetime with the 3-branes replaced by an event horizon. As the temperature of the Universe cools down, phase transitions are expected to take place, and the intermediate and IR branes come out from behind the event horizon. The Goldberger-Wise mechanism for radion stabilization has a well-known problem of having a supercooled phase transition, which typically does not get completed in time. This problem is even more severe when an intermediate brane is introduced, whose scale is well above TeV, as the corresponding Hubble rate is much larger. We circumvent the problem by employing an alternative mechanism for radion stabilization with dark Yang-Mills fields, which prevents a long supercooling epoch, but still allows the strong first order phase transitions. As a result, the phase transitions in our multi-brane Universe predict a stochastic gravitational wave background with a unique multi-peak signature, which is within the sensitivity reach of future space-based gravitational wave observers. We also show that there are $N-1$ radions for an $N$ 3-brane set-up, unlike a recent claim that there exists only one radion.

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S. Girmohanta, S. Lee, Y. Nakai, et. al.
Thu, 13 Apr 23
1/59

Comments: 34 pages, 6 figures

Cosmological constraints from standardized non-CMB observations [CEA]

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http://arxiv.org/abs/2304.05522


The current expansion of the Universe has been observed to be accelerating, and the widely accepted spatially-flat concordance model of general relativistic cosmology attributes this phenomenon to a constant dark energy, a cosmological constant, which is measured to comprise about 70% of the total energy budget of the current Universe. However, observational discrepancies and theoretical puzzles have raised questions about this model, suggesting that alternative cosmological models with non-zero spatial curvature and/or dark energy dynamics might provide better explanations.
To explore these possibilities, we have conducted a series of studies using standardized, lower-redshift observations to constrain six different cosmological models with varying degrees of flatness and dark energy dynamics. Through comparing these observations with theoretical predictions, we aim to deepen our understanding of the evolution of the Universe and shed new light on its mysteries. Our data provide consistent cosmological constraints across all six models, with some suggesting the possibility of mild dark energy dynamics and slight spatial curvature. However, these joint constraints do not rule out the possibility of dark energy being a cosmological constant and the spatial hypersurfaces being flat. Overall, our findings contribute to the ongoing efforts to refine our understanding of the Universe and its properties, and suggest that multiple cosmological models remain viable.

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S. Cao
Thu, 13 Apr 23
10/59

Comments: Ph.D. thesis, Kansas State University

Cosmic Strings from Thermal Inflation [CEA]

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http://arxiv.org/abs/2304.05666


Thermal inflation was proposed as a mechanism to dilute the density of cosmological moduli. Thermal inflation is driven by a complex scalar field possessing a large vacuum expectation value and a very flat potential, called a `flaton’. Such a model admits cosmic string solutions, and a network of such strings will inevitably form in the symmetry breaking phase transition at the end of the period of thermal inflation. We discuss the differences of these strings compared to the strings which form in the Abelian Higgs model. Specifically, we find that the upper bound on the symmetry breaking scale is parametrically lower than in the case of Abelian Higgs strings, and that the lower cutoff on the string loop distribution is determined by cusp annihilation rather than by gravitational radiation (for the value of the transition temperature proposed in the original work on thermal inflation).

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R. Brandenberger and A. Favero
Thu, 13 Apr 23
31/59

Comments: 6 pages

Self-resonant Dark Matter [CL]

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http://arxiv.org/abs/2304.05942


We present a review on the self-resonant dark matter scenarios where multiple components of dark matter give rise to a resonant condition in the $u$-channel diagrams for their comparable masses. In this case, there is no need of lighter mediators for enhancing the self-scattering and annihilation cross sections for dark matter. We discuss the velocity-dependent self-scattering for the small-scale problems, the relic density of self-resonant dark matter, and the observable signatures in indirect and detection experiments.

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H. Lee
Thu, 13 Apr 23
39/59

Comments: 7 pages, 4 figures. To appear in the proceedings for the 19th Rencontres du Vietnam Theory Meeting Experiment (TMEX) 2023

Monomial warm inflation revisited [CEA]

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http://arxiv.org/abs/2304.05978


We revisit the idea that the inflaton may have dissipated part of its energy into a thermal bath during inflation, considering monomial inflationary potentials and three different forms of dissipation rate. Using a numerical Fokker-Planck approach to describe the stochastic dynamics of inflationary fluctuations, we confront this scenario with current bounds on the spectrum of curvature fluctuations and primordial gravitational waves. We also obtain analytical approximations that outperform those frequently used in previous analyses. We show that only our numerical Fokker-Planck method is accurate, fast and precise enough to test these models against current data. We advocate its use in future studies of warm inflation. We also apply the stochastic inflation formalism to this scenario, finding that a commonly implemented large thermal correction to the primordial spectrum–that had been argued to become apparent with it–is actually not required. Improved bounds on the scalar spectral index will further constrain warm inflation in the near future.

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G. Ballesteros, A. Rodríguez and M. Pierre
Thu, 13 Apr 23
55/59

Comments: 55 pages, 12 figures

Galileon inflation evades the no-go for PBH formation in the single-field framework [CEA]

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http://arxiv.org/abs/2304.04065


We consider Galileon inflation in the Effective Field Theory (EFT) framework and examine the possibility for PBH formation during slow roll (SR) to ultra slow roll (USR) transitions. We show that loop corrections to the power spectrum, in this case, do not impose additional constraints on the masses of PBHs produced. We indicate that the remarkable non-renormalization property of Galileon due to generalized shift symmetry is responsible for protecting PBH formation from quantum loop corrections.

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S. Choudhury, S. Panda and M. Sami
Tue, 11 Apr 23
26/63

Comments: 44 pages, 2 figures, Comments are welcome

Perils of Towers in the Swamp: Dark Dimensions and the Robustness of Effective Field Theories [CL]

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http://arxiv.org/abs/2304.03902


Recently there has been an interesting revival of the idea to use large extra dimensions to address the dark energy problem, exploiting the (true) observation that towers of states with masses split, by $M^2_N = f(N) m^2,$ with $f$ an unbounded function of the integer $N$, sometimes contribute to the vacuum energy only an amount of order $m^D$ in $D$ dimensions. It has been argued that this fact is a consequence of swampland conjectures and may require a departure from Effective Field Theory (EFT) reasoning. We test this claim with calculations for Casimir energies in extra dimensions. We show why the domain of validity for EFTs ensures that the tower spacing scale $m$ is always an upper bound on the UV scale for the lower-energy effective theory; use of an EFT with a cutoff part way up a tower is not a controlled approximation. We highlight the role played by the sometimes-suppressed contributions from towers in extra-dimensional approaches to the cosmological constant problem, old and new, and point out difficulties encountered in exploiting it. We compare recent swampland realizations of these arguments with earlier approaches using standard EFT examples, discussing successes and limitations of both.

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C. Burgess and F. Quevedo
Tue, 11 Apr 23
28/63

Comments: 11 pages, 1 figure

Aspects of Everpresent $Λ$ (I): A Fluctuating Cosmological Constant from Spacetime Discreteness [CL]

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http://arxiv.org/abs/2304.03819


We provide a comprehensive discussion of the Everpresent $\Lambda$ cosmological model arising from fundamental principles in causal set theory and unimodular gravity. In this framework the value of the cosmological constant ($\Lambda$) fluctuates, in magnitude and in sign, over cosmic history. At each epoch, $\Lambda$ stays statistically close to the inverse square root of the spacetime volume. Since the latter is of the order of $H^2$ today, this provides a way out of the cosmological constant puzzle without fine tuning. Our discussion includes a review of what is known about the topic as well as new motivations and insights supplementing the original arguments. We also study features of a phenomenological implementation of this model, and investigate the statistics of simulations based on it. Our results show that while the observed values of $H_0$ and $\Omega_\Lambda^0$ are not typical outcomes of the model, they can be achieved through a modest number of simulations. We also confirm some expected features of $\Lambda$ based on this model, such as the fact that it stays statistically close to the value of the total ambient energy density (be it matter or radiation dominated), and that it is likely to change sign roughly every Hubble timescale.

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S. Das, A. Nasiri and Y. Yazdi
Tue, 11 Apr 23
31/63

Comments: 28 pages, 10 figures

MSSM-inflation revisited: Towards a coherent description of high-energy physics and cosmology [CL]

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http://arxiv.org/abs/2304.04534


The aim of this paper is to highlight the challenges and potential gains surrounding a coherent description of physics from the high-energy scales of inflation down to the lower energy scales probed in particle-physics experiments. As an example, we revisit the way inflation can be realised within an effective Minimal Supersymmetric Standard Model (eMSSM), in which the $LLe$ and $udd$ flat directions are lifted by the combined effect of soft-supersymmetric-breaking masses already present in the MSSM, together with the addition of effective non-renormalizable operators. We clarify some features of the model and address the question of the one-loop Renormalization Group improvement of the inflationary potential, discussing its impact on the fine-tuning of the model. We also compare the parameter space that is compatible with current observations (in particular the amplitude, $A_{\scriptscriptstyle{\mathrm{S}}}$, and the spectral index, $n_{\scriptscriptstyle{\mathrm{S}}}$, of the primordial cosmological fluctuations) at tree level and at one loop, and discuss the role of reheating. Finally we perform combined fits of particle and cosmological observables (mainly $A_{\scriptscriptstyle{\mathrm{S}}}$, $n_{\scriptscriptstyle{\mathrm{S}}}$, the Higgs mass, and the cold-dark-matter energy density) with the one-loop inflationary potential applied to some examples of dark-matter annihilation channels (Higgs-funnel, Higgsinos and A-funnel), and discuss the status of the ensuing MSSM spectra with respect to the LHC searches.

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G. Weymann-Despres, S. Henrot-Versillé, G. Moultaka, et. al.
Tue, 11 Apr 23
62/63

Comments: 38 pages, 7 figures

Accelerating universe at the end of time [CL]

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http://arxiv.org/abs/2303.03418


We investigate whether an accelerating universe can be realized as an asymptotic late-time solution of FLRW-cosmology with multi-field multi-exponential potentials. Late-time cosmological solutions exhibit a universal behavior which enables us to bound the rate of time variation of the Hubble parameter. In string-theoretic realizations, if the dilaton remains a rolling field, our bound singles out a tension in achieving asymptotic late-time cosmic acceleration. Our findings go beyond previous no-go theorems in that they apply to arbitrary multi-exponential potentials and make no specific reference to vacuum or slow-roll solutions. We also show that if the late-time solution approaches a critical point of the dynamical system governing the cosmological evolution, the criterion for cosmic acceleration can be generally stated in terms of a directional derivative of the potential.

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G. Shiu, F. Tonioni and H. Tran
Mon, 10 Apr 23
30/36

Comments: 6 pages + appendix

Anisotropic Hubble Expansion in Pantheon+ Supernovae [CEA]

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http://arxiv.org/abs/2304.02718


We decompose the Pantheon+ Type Ia supernovae (SN) sample in hemispheres on the sky finding angular variations up to $4$ km/s/Mpc in the Hubble constant $H_0$ both in the SH0ES redshift range $0.0233 < z < 0.15$ and in the extended redshift range $0.01 < z < 0.7$. We assume the $\Lambda$CDM model, so our findings become model dependent in extended redshift ranges. $H_0$ is larger in a hemisphere encompassing the CMB dipole direction. The variations we see exceed the errors on the recent SH0ES determination, $H_0 = 73.04 \pm 1.04$ km/s/Mpc, but are not large enough to explain early versus late Universe discrepancies in the Hubble constant. The removal of low redshift SN leads to a weakening of angular $H_0$ variations, but we confirm that they persist beyond the influence of the Shapley supercluster $z > 0.06$

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R. McConville and E. Colgáin
Fri, 7 Apr 23
6/50

Comments: 4 pages, 7 figures. Comments welcome

$\mathbf {SU(\infty)}$-QGR Quantumania: Everything, Everywhere, All At Once [CL]

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http://arxiv.org/abs/2304.02761


$SU(\infty)$-QGR is a quantum approach to Universe and gravity. Its main assumption is infinite mutually commuting observables in the Universe, leading to representation of $SU(\infty)$ by its Hilbert spaces and those of its subsystems. The Universe as a whole is static, topological, and characterized by two continuous parameters. Nonetheless, quantum fluctuations induce clustering and finite rank internal symmetries, which approximately divide the Universe to infinite interacting subsystems. Their Hilbert space depends on an additional dimensionful parameter, and selection of a subsystem as clock induces a relative dynamics, with $SU(\infty)$ sector as gravity. The Lagrangian defined on the (3+1)-dimensional parameter space is Yang-Mills for both symmetries. When quantumness of gravity is undetectable, it is perceived as curvature of an effective spacetime.

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H. Ziaeepour
Fri, 7 Apr 23
21/50

Comments: 12 pages, no figure. Essay submitted to 2023 Awards for Essays on Gravitation

Axial perturbations of black holes in scalar-tensor gravity: near-horizon behaviour [CL]

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http://arxiv.org/abs/2304.03055


We consider axial (or odd-parity) perturbations of non-spinning hairy black holes (BH) in shift-symmetric DHOST (Degenerate Higher-Order Scalar-Tensor) theories, including terms quartic and cubic in second derivatives of the scalar field. We give a new formulation of the effective metric in which axial perturbations propagate as in general relativity. We then introduce a generic parametrization of the effective metric in the vicinity of the background BH horizon. Writing the dynamics of the perturbations in terms of a Schr\”odinger-like operator, we discuss in which cases the operator is (essentially) self-adjoint, thus leading to an unambiguous time evolution, according to the choice of parameters characterizing the near-horizon effective metric. This is in particular useful to investigate the stability of the perturbations. We finally illustrate our general analysis with two examples of BH solutions.

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K. Noui, H. Roussille and D. Langlois
Fri, 7 Apr 23
34/50

Comments: 24 pages, 3 appendices

Eternal binaries [CL]

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http://arxiv.org/abs/2304.02039


The two-body problem is extensively studied in open systems and asymptotically flat spacetimes. However, there are many systems where radiation is trapped: they range from radiating charges in cavities to low-energy excitations of massive degrees of freedom, to anti-de Sitter spacetimes. Here, we study the problem of motion of a pointlike particle orbiting a massive compact object inside a cavity. We first show that – assuming circular motion – there are initial conditions for which the self-force vanishes and the binary is eternal. We then consider the evolution of the system under radiation reaction in a toy model which we argue captures the essentials of orbiting particles. We show that eternal circular binaries may exist. We also show that the presence of cavity modes leads to chaos in regimes of strong coupling or when the system is initialized close enough to a resonance. Our results have implications for physics in anti-de Sitter spacetimes and possibly for binaries evolving within dark matter haloes, if it consists on massive fundamental fields.

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J. Redondo-Yuste, V. Cardoso, C. Macedo, et. al.
Thu, 6 Apr 23
2/76

Comments: 21 pages, 17 figures

Gravitoelectric dynamical tides at second post-Newtonian order [CL]

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http://arxiv.org/abs/2304.02030


We present a gravitoelectric quadrupolar dynamical tidal-interaction Hamiltonian for a compact binary system, that is valid to second order in the post-Newtonian expansion. Our derivation uses the diagrammatic effective field theory approach, and involves Feynman integrals up to two loops, evaluated with the dimensional regularization scheme. We also derive the effective Hamiltonian for adiabatic tides, obtained by taking the appropriate limit of the dynamical effective Hamiltonian, and we check its validity by verifying the complete Poincar\’e algebra. In the adiabatic limit, we also calculate two gauge-invariant observables, namely, the binding energy for a circular orbit and the scattering angle in a hyperbolic scattering. Our results are important for developing accurate gravitational waveform models for neutron-star binaries for present and future gravitational-wave observatories.

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M. Mandal, P. Mastrolia, H. Silva, et. al.
Thu, 6 Apr 23
23/76

Comments: 20 pages, 2 figures, 1 table

Primordial Black Hole Leptogenesis in Supersymmetry [CL]

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http://arxiv.org/abs/2304.02604


We have studied the role of Hawking evaporation of primordial black hole in the production of the supersymmetric particles like sneutrinos – the super-partner of heavy right handed neutrinos. Considering lepton number violating decays of such particles and $CP$ violating phases due to soft supersymmetry breaking terms, we have obtained the baryonic asymmetry of the universe which depends on the mass of primordial black holes. Apart from CMB and BBN constraints on such mass, we have shown more stringent upper bound on this mass from the requirement of black hole evaporation temperature to be above the temperature required for almost first order phase transition so that leptogenesis could create the observed baryonic asymmetry. We have shown how the primordial black hole mass, heavy right handed neutrino mass and soft supersymmetry breaking parameters are related from the requirement of successful leptogenesis and the allowed parameter space to avoid gravitino problem. Considering experimental constraint on branching ratio of $\mu \rightarrow e \gamma $, we have shown the connection of right handed neutrino mass scale with the lower bound of the typical mass scale of supersymmetric particles.

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S. Khan and R. Adhikari
Thu, 6 Apr 23
46/76

Comments: 14 pages, 3 figures