Tag Archives: High Energy Physics – Theory

Minimal decoherence from inflation [CL]

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http://arxiv.org/abs/2211.11046


We compute the rate with which super-Hubble cosmological fluctuations are decohered during inflation, by their gravitational interactions with unobserved shorter-wavelength scalar and tensor modes. We do so using Open Effective Field Theory methods, that remain under control at the late times of observational interest, contrary to perturbative calculations. Our result is minimal in the sense that it only incorporates the self-interactions predicted by General Relativity in single-clock models (additional interaction channels should only speed up decoherence). We find that decoherence is both suppressed by the first slow-roll parameter and by the energy density during inflation in Planckian units, but that it is enhanced by the volume comprised within the scale of interest, in Hubble units. This implies that, for the scales probed in the Cosmic Microwave Background, decoherence is effective as soon as inflation proceeds above $\sim 5\times 10^{9}$ GeV. Alternatively, if inflation proceeds at GUT scale decoherence is incomplete only for the scales crossing out the Hubble radius in the last ~ 13 e-folds, of inflation. We also compute how short-wavelength scalar modes decohere primordial tensor perturbations, finding a faster rate unsuppressed by slow-roll parameters. Identifying the parametric dependence of decoherence, and the rate at which it proceeds, helps suggest ways to look for quantum effects.

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C. Burgess, R. Holman, G. Kaplanek, et. al.
Tue, 22 Nov 22
51/83

Comments: 31 pages + appendices, 7 figures

Perspectives on the Dark Sector [CL]

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http://arxiv.org/abs/2211.11273


I present some new perspectives on Dark Matter, Dark Energy and the origin of structure in the Universe. First, I argue that in order to understand the two latter issues, one needs to go beyond a standard point particle effective field theory analysis. Next, I review recent work attempting to construct a unified dark sector model from Heterotic superstring theory. I finish by discussing a new research effort to obtain early Universe cosmology directly from a non-perturbative definition of superstring theory.

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R. Brandenberger
Tue, 22 Nov 22
53/83

Comments: Invited concluding talk, 33rd Rencontres de Blois

Entanglement masquerading in the CMB [CL]

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http://arxiv.org/abs/2211.11079


The simplest single-field inflation models capture all the relevant contributions to the patterns in the Cosmic Microwave Background (CMB) observed today. A key assumption in these models is that the quantum inflationary fluctuations that source such patterns are generated by a particular quantum state — the Bunch-Davies (BD) state. While this is a well-motivated choice from a theoretical perspective, the question arises of whether current data can rule out other, also well motivated, choices of states. In particular, as we previously demonstrated in arXiv:2104.13410 [hep-th], entanglement is naturally and inevitably dynamically generated during inflation given the presence of a “rolling” spectator scalar field — and the resulting entangled state will yield a primordial power spectrum with potentially measurable deviations compared to the canonical BD result. For this work we developed a perturbative framework to allow a systematic exploration of constraints on (or detection of) entangled states with Planck CMB data using Monte Carlo techniques. We have found that most entangled states accessible with our framework are consistent with the data. One would have to expand the framework to allow a greater variety of entangled states in order to saturate the Planck constraints and more systematically explore any preferences the data may have among the different possibilities.

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A. Adil, A. Albrecht, R. Baunach, et. al.
Tue, 22 Nov 22
55/83

Comments: 37 pages, 12 figures, 3 appendices

Probing de Sitter from the horizon [CL]

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http://arxiv.org/abs/2211.11672


In a QFT on de Sitter background, one can study correlators between fields pushed to the future and past horizons of a comoving observer. This is a neat probe of the physics in the observer’s causal diamond (known as the static patch). We use this observable to give a generalization of the quasinormal spectrum in interacting theories, and to connect it to the spectral density that appears in the K\”all\’en-Lehmann expansion of dS correlators. We also introduce a finite-temperature effective field theory consisting of free bulk fields coupled to a boundary. In matching it to the low frequency expansion of correlators, we find positivity constraints on the EFT parameters following from unitarity.

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M. Mirbabayi and F. Riccardi
Tue, 22 Nov 22
57/83

Comments: 24 pages, 3 figures

General Effective Field Theory of Teleparallel Gravity [CL]

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http://arxiv.org/abs/2211.11420


We construct the Effective Field Theory (EFT) of the teleparallel equivalent of general relativity (TEGR). Firstly, we present the necessary field redefinitions of the scalar field and the tetrads. Then we provide all the terms at next-to-leading-order, containing the torsion tensor and its derivatives, and derivatives of the scalar field, accompanied by generic scalar-field-dependent couplings, where all operators are suppressed by a scale $\Lambda$. Removing all redundant terms using the field redefinitions we result to the EFT of TEGR, which includes significantly more terms comparing to the EFT of General Relativity. Finally, we present an application in a cosmological framework. Interestingly enough, although GR and TEGR are completely equivalent at the level of classical equations, we find that their corresponding EFTs possess minor but non-zero differences. Hence, we do verify that at higher energies the excitation and the features of the extra degrees of freedom are slightly different in the two theories, thus making them theoretically distinguishable. Nevertheless, we mention that these differences are suppressed by the heavy mass scale $\Lambda$ and thus it is not guaranteed that they could be measured in future experiments and observations.

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M. Mylova, J. Said and E. Saridakis
Tue, 22 Nov 22
78/83

Comments: 16 pages, comments are welcome

Holographic origin of TCC and the Distance Conjecture [CL]

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http://arxiv.org/abs/2211.09128


One of the unique features of quantum gravity is the lack of local observables and the completeness of boundary observables. We show that the existence of boundary observables in scalar field cosmologies where $a(t)\sim t^{p}$ is equivalent to TCC, which implies $p\leq 1$. Moreover, the mass of weakly-coupled particles must decay like $m\lesssim t^{1-2p}$ to ensure that they yield non-trivial boundary observables. This condition can be expressed in terms of the scalar field that drives the cosmology as $m\lesssim\exp(-c\phi)$ where $c$ depends on the scalar potential. The strongest bound we find is achieved for $V\sim \exp(-2\phi/\sqrt{d-2})$ where $c=1/\sqrt{d-2}$. These results connect some of the most phenomenologically interesting Swampland conjectures to the most basic version of holography.

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A. Bedroya
Fri, 18 Nov 22
31/70

Comments: 34 pages, 6 figures

Ending inflation with a bang: Higgs vacuum decay in $R^2$ gravity [CEA]

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http://arxiv.org/abs/2211.09244


According to the current experimental data, the Higgs vacuum appears to be metastable due to the development of a second lower ground state in its potential. Consequently, vacuum decay would induce the nucleation of true vacuum bubbles with catastrophic consequences for our Universe and therefore we are motivated to study possible stabilising mechanisms in the early universe. In our latest investigation (2207.00696), we studied the electroweak metastability in the context of the observationally favoured model of Starobinsky inflation. Following the motivation and techniques from our first study (2011.037633), we obtained constraints on the Higgs curvature coupling $\xi$, while embedding the SM on the modified gravity scenario $R+R^2$, which introduces Starobinsky inflation naturally. This had significant repercussions for the effective Higgs potential in the form of additional negative terms that destabilize the false vacuum. Another important aspect lay in the definition for the end of inflation, as bubble nucleation is most prominent during its very last moments. Our results dictated that these stronger lower $\xi$-bounds are very sensitive to the final moments of inflation, where spacetime deviates increasingly from de Sitter.

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A. Mantziris
Fri, 18 Nov 22
44/70

Comments: 6 pages, 2 figures, based on the parallel talk at the International Conference of High Energy Physics (6-13 July 2022) hosted by the INFN sections and Universities of Bologna and Ferrara

Gravitational Waves from dark composite dynamics [CL]

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http://arxiv.org/abs/2211.08877


We discuss the stochastic gravitational-wave spectrum from dark confinement and chiral phase transitions in the early Universe. Specifically, we look at pure Yang-Mills theory for an arbitrary number of colours as well as SU(3) with quarks in different representations. We utilise thermodynamic lattice data and map it to effective models, such as the Polyakov-loop and the PNJL model. This allows us to compute gravitational-wave parameters and the corresponding gravitational-wave signal. We compare the signal to future gravitational-wave observatories such as the Big Bang Observer and DECIGO.

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M. Reichert and Z. Wang
Thu, 17 Nov 22
38/63

Comments: 8 pages, 3 figures, contribution to the proceedings of the XVth Quark Confinement and the Hadron Spectrum conference at the University of Stavanger

Reduced Axion Abundance from an Extended Symmetry [CL]

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http://arxiv.org/abs/2211.07661


In recent work we showed that the relic dark matter abundance of QCD axions can be altered when the Peccei-Quinn (PQ) field is coupled to very light scalar/s, rendering the effective axion mass dynamical in the early universe. In this work we develop this framework further, by introducing a new extended symmetry group to protect the new particles’ mass. We find that with a new global $SO(N)$ symmetry, with large $N$, we can not only account for the lightness of the new scalars, but we can reduce the axion relic abundance in a technically natural way. This opens up the possibility of large PQ scales, including approaching the GUT scale, and still naturally producing the correct relic abundance of axions. Also, in these models the effective PQ scale is relatively small in the very early universe, and so this can help towards alleviating the isocurvature problem from inflation. Furthermore, instead of possible over-closure from cosmic strings, the extended symmetry implies the formation of non-topological textures which provide a relatively small abundance.

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I. Allali, M. Hertzberg and Y. Lyu
Wed, 16 Nov 22
10/76

Comments: 13 pages, 6 figures, in double column format

A Tilt Instability in the Cosmological Principle [CEA]

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http://arxiv.org/abs/2211.08093


We show that the Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) framework has an instability towards the growth of fluid flow anisotropies, even if the Universe is accelerating. This flow (tilt) instability in the matter sector is invisible to Cosmic No-Hair Theorem-like arguments, which typically only flag shear anisotropies in the metric. We illustrate our claims in the setting of “dipole cosmology”, the maximally Copernican generalization of FLRW that can accommodate a flow. Simple models are sufficient to show that the cosmic flow need not track the shear, even in the presence of a positive cosmological constant. We also emphasize that the growth of the tilt hair is fairly generic if the total equation of state $w(t) \rightarrow -1$ at late times (as it does in standard cosmology), irrespective of the precise model of dark energy.

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C. Krishnan, R. Mondol and M. Sheikh-Jabbari
Wed, 16 Nov 22
34/76

Comments: 5 pages, 4 figures

Anisotropic constant-roll k-inflation model [CL]

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http://arxiv.org/abs/2211.08032


In this paper, we would like to figure out whether a k-inflation model admits the Bianchi type I metric as its inflationary solution under a constant-roll condition in the presence of the supergravity motivated coupling between scalar and vector fields, $f^2(\phi)F_{\mu\nu}F^{\mu\nu}$. As a result, some novel anisotropic inflationary solutions are shown to appear along with a power-law one in this scenario. Furthermore, these solutions are numerically confirmed to be attractive, in contrast to the prediction of the Hawking’s cosmic no-hair conjecture.

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D. Nguyen, T. Pham, T. Le, et. al.
Wed, 16 Nov 22
46/76

Comments: 15 pages, 11 figures. To appear in Communications in Physics (2023), a well-established physics journal of Vietnam. Comments are welcome

Constraining the Lorentz-Violating Bumblebee Vector Field with Big Bang Nucleosynthesis and Gravitational Baryogenesis [CL]

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http://arxiv.org/abs/2211.07934


By keeping the cosmological principle i.e., an isotropic and homogeneous universe, we consider the cosmology of a vector-tensor theory of gravitation known as the \textit{bumblebee} model. In this model a single Lorentz-violating timelike vector field with a nonzero vacuum expectation value (VEV) couples to the Ricci tensor and scalar, as well. Taking the ansatz $B(t)\sim t^\beta$ for the time evolution of the vector field we derive the relevant dynamic equations of the Universe, where $\beta$ is a free parameter. In particular, by employing observational data coming from the Big Bang Nucleosynthesis (BBN) and the matter-antimatter asymmetry in the Baryogenesis era, we impose some constraints on the VEV of the bumblebee timelike vector field i.e., $\xi b^2$, and the exponent parameter $\beta$. The former and the latter limit the size of Lorentz violation, and the rate of the time evolution of the background Lorentz-violating bumblebee field, respectively.

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M. Khodadi, G. Lambiase and A. Sheykhi
Wed, 16 Nov 22
51/76

Comments: 16 pages (two columns), 5 figures

Gravitational waves and tadpole resummation: Efficient and easy convergence of finite temperature QFT [CL]

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http://arxiv.org/abs/2211.08218


We demonstrate analytically and numerically that “optimized partial dressing” (OPD) thermal mass resummation, which uses gap equation solutions inserted into the tadpole, efficiently tames finite temperature perturbation theory calculations of the effective thermal potential, without necessitating use of the high-temperature approximation. An analytical estimate of the scale dependence for OPD resummation, standard Parwani Daisy-resummation and dimensional reduction shows that OPD has similar scale dependence to dimensional reduction, greatly improved over Parwani resummation. We also elucidate how to construct and solve the gap equation for realistic numerical calculations, and demonstrate OPD’s improved accuracy and precision for a toy scalar model. An example of the physical significance of OPD’s improved accuracy is the maximal gravitational wave amplitude that a model is capable of generating, which Parwani resummation underestimates by two orders of magnitude. This highlights the need to bring theoretical uncertainties under control even when analysing broad features of a model. Given the simplicity of the OPD compared to two loop dimensional reduction, as well as the ease with which this scheme handles departures from the high temperature expansion, we argue this scheme has great potential in analyzing the parameter space of realistic BSM models.

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D. Curtin, J. Roy and G. White
Wed, 16 Nov 22
52/76

Comments: 30 pages, 5 figures, 1 table

Cosmic decoherence: primordial power spectra and non-Gaussianities [CEA]

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http://arxiv.org/abs/2211.07598


We study the effect of quantum decoherence on the inflationary cosmological perturbations. This process might imprint specific observational signatures revealing the quantum nature of the inflationary mechanism being related to the longstanding issue of the quantum-to-classical transition of inflationary fluctuations. Several works have investigated the effect of quantum decoherence on the statistical properties of primordial fluctuations. In particular, it has been shown that cosmic decoherence leads to corrections to the curvature power spectrum predicted by standard slow-roll inflation. Equally interesting, a non zero curvature trispectrum has been shown to be purely induced by cosmic decoherence, but surprisingly, decoherence seems not to generate any bispectrum. We further develop such an analysis by adopting a generalized form of the pointer observable, showing that decoherence does induce a non vanishing curvature bispectrum and providing a specific underlying concrete physical process. Present constraints on primordial bispectra allow to put an upper bound on the strength of the environment-system interaction. In full generality, the decoherence-induced bispectrum can be scale dependent provided one imposes the corresponding correction to the power spectrum to be scale independent. Such scale dependence on the largest cosmological scales might represent a distinctive imprint of the quantum decoherence process taking place during inflation. We also provide a criterion that allows to understand when cosmic decoherence induces scale independent corrections, independently of the type of environment considered. As a final result, we study the effect of cosmic decoherence on tensor perturbations and we derive the decoherence corrected tensor-to-scalar perturbation ratio. In specific cases, decoherence induces a blue tilted correction to the standard tensor power spectrum.

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A. Hammou and N. Bartolo
Tue, 15 Nov 22
8/103

Comments: 56 pages, 6 figures

Snowmass 2021 Dark Matter Complementarity Report [CL]

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http://arxiv.org/abs/2211.07027


The fundamental nature of Dark Matter is a central theme of the Snowmass 2021 process, extending across all Frontiers. In the last decade, advances in detector technology, analysis techniques and theoretical modeling have enabled a new generation of experiments and searches while broadening the types of candidates we can pursue. Over the next decade, there is great potential for discoveries that would transform our understanding of dark matter. In the following, we outline a road map for discovery developed in collaboration among the Frontiers. A strong portfolio of experiments that delves deep, searches wide, and harnesses the complementarity between techniques is key to tackling this complicated problem, requiring expertise, results, and planning from all Frontiers of the Snowmass 2021 process.

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A. Boveia, M. Berkat, T. Chen, et. al.
Tue, 15 Nov 22
53/103

Comments: 10 pages, 5 figures. Version prepared for inclusion in the Snowmass Book. Extended version at arXiv:2210.01770

Reconciling cosmic dipolar tensions with a gigaparsec void [CEA]

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http://arxiv.org/abs/2211.06857


Recent observations indicate a $4.9\sigma$ tension between the CMB and quasar dipoles. This tension challenges the cosmological principle. We propose that if we live in a gigaparsec scale void, the CMB and quasar dipolar tension can be reconciled. This is because we are unlikely to live at the center of the void. And a 15% offset from the center will impact the quasars and CMB differently in their dipolar anisotropies. As we consider a large and thick void, our setup can also ease the Hubble tension.

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T. Cai, Q. Ding and Y. Wang
Tue, 15 Nov 22
68/103

Comments: 5 pages, 4 figures

Early and late time cosmology: the $f(R)$ gravity perspective [CL]

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http://arxiv.org/abs/2211.06268


Discrepancies between observations at early and late cosmic epochs, and the vacuum energy problem associated with the interpretation of cosmological constant, are questioning the $\Lambda$CDM model. Motivated by these conceptual and observational facts, extensions of Einstein’s gravity are recently intensively considered in view of curing unsolved issues suffered by General Relativity at ultraviolet and infrared scales. Here, we provide a short overview of some aspects of $f(R)$ gravity, focusing, in particular, on cosmological applications. Specifically, Noether symmetries are adopted as a criterion to select viable models and investigate the corresponding dynamics. We thus find solutions to the cosmological field equations, analyzing the behaviour of selected models from the matter-dominated to the present epoch. Moreover, constraints coming from energy conditions and the so-called swampland criteria are also considered. In particular, we qualitatively discuss the possibility of $f(R)$ gravity to account for fixing cosmic tensions.

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F. Bajardi, R. D’Agostino, M. Benetti, et. al.
Mon, 14 Nov 22
30/69

Comments: 11 pages, 1 figure, Accepted for publication in EPJP

Twenty years of Dark Matter searches with INTEGRAL/SPI [HEAP]

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http://arxiv.org/abs/2211.06200


Based on almost 20 years of data collected by the high-resolution spectrometer SPI on board the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) we present constraints on a decaying dark matter particle manifesting itself via a narrow line-like spectral feature. Our ON-OFF type analysis of the Milky Way observations allowed us to constrain the lifetime to be $\gtrsim 10^{20}-10^{21}$ yrs for DM particles with masses $40\,\text{keV}\,<\,M_{\text{DM}}\,<\,14\,\text{MeV}$. Within this mass range our analysis also reveals 32 line-like features detected at $\geq 3\sigma$ significance, 29 of which coincide with known instrumental and astrophysical lines. In particular, we report on the detection of the electron-positron annihilation (511 keV) and $^{26}$Al (1809 keV) lines with spatial profiles consistent with previous results in the literature. For the particular case of the sterile neutrino DM we report the limits on the mixing angle as a function of sterile neutrino mass. We discuss the dominant impact of systematic uncertainties connected to the strongly time-variable INTEGRAL/SPI instrumental background as well as the ones connected to the uncertainties of MW DM density profile measurements on the derived results.

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S. Fischer, D. Malyshev, L. Ducci, et. al.
Mon, 14 Nov 22
38/69

Comments: N/A

Circumventing the challenges in the choice of the non-conformal coupling function in inflationary magnetogenesis [CEA]

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http://arxiv.org/abs/2211.05834


[Abridged] As is well known, in order to generate magnetic fields of observed amplitudes during inflation, the conformal invariance of the electromagnetic field has to be broken by coupling it either to the inflaton or to the scalar curvature. Couplings to scalar curvature pose certain challenges even in slow roll inflation and it seems desirable to consider couplings to the inflaton. It can be shown that, in slow roll inflation, to generate nearly scale invariant magnetic fields of adequate strengths, the non-conformal coupling to the inflaton has to be chosen specifically depending on the inflationary model at hand. In a recent work, we had found that, when there arise sharp departures from slow roll inflation leading to strong features in the scalar power spectra, there inevitably arise sharp features in the spectra of the electromagnetic fields, unless the non-conformal coupling functions are extremely fine tuned. In particular, we had found that, if there occurs an epoch of ultra slow roll inflation, then the strength of the magnetic field over large scales can be severely suppressed. In this work, we examine whether these challenges can be circumvented in models of inflation involving two fields. We show that the presence of the additional scalar field allows us to construct coupling functions that lead to magnetic fields of required strengths even when there arise intermediate epochs of ultra slow roll inflation. However, we find that the features in the spectra of the magnetic fields that are induced due to the departures from slow roll inflation cannot be completely ironed out. We make use of the code MagCAMB to calculate the effects of the magnetic fields on the anisotropies in the cosmic microwave background and investigate if the spectra with features are broadly consistent with the current constraints.

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S. Tripathy, D. Chowdhury, H. Ragavendra, et. al.
Mon, 14 Nov 22
51/69

Comments: 21 pages, 8 figures

Cosmological tensions in the birthplace of the heliocentric model [CEA]

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http://arxiv.org/abs/2211.05248


The theme of tensions in cosmology has become increasingly important in the cosmological community, proving capable of attracting new generations of scientists who want to be there and contribute to the next paradigm shift.

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E. Valentino, E. Saridakis and A. Riess
Fri, 11 Nov 22
5/58

Comments: 3 pages, 1 figure, meeting report for Nature Astronomy

No Smooth Spacetime in Lorentzian Quantum Cosmology and Trans-Planckian Physics [CL]

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http://arxiv.org/abs/2211.05306


In minisuperspace quantum cosmology, the Lorentzian path integral formulations of the no-boundary and tunneling proposals have recently been analyzed. But it has been pointed out that the wave function of linearized perturbations around a homogeneous and isotropic background is of an inverse Gaussian form and thus that their correlation functions are divergent. In this paper, we revisit this issue and consider the problem of perturbations in Lorentzian quantum cosmology by modifying the dispersion relation based on trans-Planckian physics. We consider two modified dispersion relations, the generalized Corley-Jacobson dispersion relation with higher momentum terms and the Unruh dispersion relation with a trans-Planckian mode cut-off, as examples. We show that the inverse Gaussian problem of perturbations in Lorentzian quantum cosmology is hard to overcome with the trans-Planckian physics modifying the dispersion relation at short distances.

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H. Matsui, S. Mukohyama and A. Naruko
Fri, 11 Nov 22
6/58

Comments: 24 pages, 11 figures

Snowmass Theory Frontier Report [CL]

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http://arxiv.org/abs/2211.05772


This report summarizes the recent progress and promising future directions in theoretical high-energy physics (HEP) identified within the Theory Frontier of the 2021 Snowmass Process.

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N. Craig, C. Csáki, A. El-Khadra, et. al.
Fri, 11 Nov 22
23/58

Comments: N/A

Comparing Accretion Disks and Dark Matter Spikes in Intermediate Mass Ratio Inspirals [CL]

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http://arxiv.org/abs/2211.05145


Intermediate Mass Ratio Inspirals (IMRIs) will be observable with space-based gravitational wave detectors such as the Laser Interferometer Space Antenna (LISA). To this end, the environmental effects in such systems have to be modeled and understood. These effects can include (baryonic) accretion disks and dark matter (DM) overdensities, so called spikes. For the first time, we model an IMRI system with both an accretion disk and a DM spike present and compare their effects on the inspiral and the emitted gravitational wave signal. We study the eccentricity evolution, employ the braking index and derive the dephasing index, which turn out to be complementary observational signatures. They allow us to disentangle the accretion disk and DM spike effects in the IMRI system.

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N. Becker and L. Sagunski
Fri, 11 Nov 22
30/58

Comments: 16 pages, 8 figures. Comments are welcome. Code available online at this http URL

Gauge-invariant perturbations at a quantum gravity bounce [CL]

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http://arxiv.org/abs/2211.04500


We study the dynamics of gauge-invariant scalar perturbations in cosmological scenarios with a modified Friedmann equation, such as quantum gravity bouncing cosmologies. We work within a separate universe approximation which captures wavelengths larger than the cosmological horizon; this approximation has been successfully applied to loop quantum cosmology and group field theory. We consider two variables commonly used to characterise scalar perturbations: the curvature perturbation on uniform-density hypersurfaces $\zeta$ and the comoving curvature perturbation $\mathcal{R}$. For standard cosmological models in general relativity as well as in loop quantum cosmology, these quantities are conserved and equal on super-horizon scales for adiabatic perturbations. Here we show that while these statements can be extended to a more general form of modified Friedmann equations similar to that of loop quantum cosmology, in other cases, such as the simplest group field theory bounce scenario, $\zeta$ is conserved across the bounce whereas $\mathcal{R}$ is not. We relate our results to approaches based on a second order equation for a single perturbation variable, such as the Mukhanov-Sasaki equation.

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S. Gielen and L. Mickel
Fri, 11 Nov 22
38/58

Comments: 26 pages, 6 figures

Primordial Black Holes [CEA]

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http://arxiv.org/abs/2211.05767


We review aspect of primordial black holes, i.e., black holes which have been formed in the early Universe. Special emphasis is put on their formation, their r\^ole as dark matter candidates and their manifold signatures, particularly through gravitational waves.

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A. Escrivà, F. Kuhnel and Y. Tada
Fri, 11 Nov 22
51/58

Comments: 117 pages, 39 figures, 555 references; to appear as invited book chapter in “Listening to the dark Universe: black holes in the era of gravitational-wave astronomy”; comments warmly welcome

Warm Inflation in $f(R,T)$ gravity [CL]

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http://arxiv.org/abs/2211.05059


In this work, we explored warm inflation in the background of $f(R,T)$ gravity in the strong dissipation regime. Considering scalar field for FLRW universe, we derived modified field equations. We then deduced slow-roll parameters under slow-roll approximations followed by power spectrum for scalar and tensor perturbations and their corresponding spectral indices. We have considered Chaotic and Natural potentials and estimated scalar spectral index and tensor-to-scalar ratio for constant as well as variable dissipation factor $\Gamma$. We found that both the rejected potentials can be revived under the context of $f(R,T)$ gravity with suitable choice of the model parameters. Further, it is seen that within the warm inflationary scenario both the potentials are consistent with Planck 2018 bounds at the Planckian and sub Planckian energy scales.

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B. Deb, S. Yeasmin and A. Deshamukhya
Thu, 10 Nov 22
47/78

Comments: 19 pages, 5 figures

Gravitational wave constraints on spatial covariant gravities [CL]

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http://arxiv.org/abs/2211.04711


The direct discovery of gravitational waves (GWs) from the coalescence of compact binary components by the LIGO/Virgo/KAGRA Collaboration provides an unprecedented opportunity for exploring the underlying theory of gravity that drives the coalescence process in the strong and highly-dynamical field regime of gravity. In this paper, we consider the observational effects of spatial covariant gravities on the propagation of GWs in the cosmological background and obtain the observational constraints on coupling coefficients in the action of spatial covariant gravities from GW observations. We first decompose the GWs into the left-hand and right-hand circular polarization modes and derive the effects of the spatial covariant gravities on the propagation equation of GWs. We find that these effects can be divided into three classes: (1) frequency-independent effects on GW speed and friction, (2) parity-violating amplitude and velocity birefringences, and (3) Lorentz-violating damping rate and dispersion of GWs. With these effects, we calculate the corresponding modified waveform of GWs generated by the coalescence of compact binaries. By comparing these new effects with the publicly available posterior samples or results from various tests of gravities with LIGO/Virgo/KAGRA data in the literature, we derive the observational constraints on coupling coefficients of the spatial covariant gravities. These results represent the most comprehensive constraints on the spatial covariant gravities in the literature.

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T. Zhu, W. Zhao and A. Wang
Thu, 10 Nov 22
60/78

Comments: 14 pages, 2 figures, and 4 tables. arXiv admin note: text overlap with arXiv:2210.05259

Impact of trans-Planckian quantum noise on the Primordial Gravitational Wave spectrum [CL]

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http://arxiv.org/abs/2211.04316


We investigate the impact of stochastic quantum noise due to trans–Planckian effects on the primordial power spectrum for gravity waves during inflation. Given an energy scale Lambda, expected to be close to the Planck scale m_Pl and larger than the Hubble scale H, this noise is described in terms of a source term in the evolution equation for comoving modes k which changes its amplitude growth from early times as long as the mode physical wavelength is smaller than Lambda^-1. We model the source term as due to a gas of black holes in the trans–Planckian regime and the corresponding Hawking radiation. In fact, for energy scales larger than, or of the order of Lambda, it is expected that trapped surfaces may form due to large energy densities. At later times the evolution then follows the standard sourceless evolution. We find that this mechanism still leads to a scale-invariant power spectrum of tensor perturbations, with an amplitude that depends upon the ratio Lambda/m_Pl.

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M. Cielo, G. Mangano and O. Pisanti
Wed, 9 Nov 22
11/76

Comments: 6 pages, 1 figure

Double-copy towards supergravity inflation with $α$-attractor models [CL]

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http://arxiv.org/abs/2211.04441


Key to the simplicity of supergravity alpha-attractor models of inflation are Volkov-Akulov fermions, often in the form of nilpotent superfields. Here we explore the possibility of using the double-copy to construct theories of Dirac-Born-Infeld-Volkov-Akulov (DBIVA) coupled to supergravity. A color-dual bootstrap admits scattering amplitudes involving pions and vectors through five-point tree-level order by order in mass-dimension, but requires the introduction of a tr(F^3) operator. Gauge theories with this operator were recently found to require a tower of higher-derivative operators to be compatible with the duality between color and kinematics. Adjoint-type double-copy construction at its most conservative seems to require the UV completion of DBVIA + pure Poincare supergravity scattering amplitudes to a family of theories involving DBVIA-like particles coupled to Weyl-Einstein supergravity. We also point out an alternative solution to color-dual gauged pions that allows adjoint double-copy without a tower of higher derivative corrections but at the cost of exchange symmetry between scalars.

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J. Carrasco, M. Lewandowski and N. Pavao
Wed, 9 Nov 22
20/76

Comments: 40 pages, 3 figures, 4 tables, ancillary data available at this url: this https URL

Exact formulations of relativistic electrodynamics and magnetohydrodynamics with helically coupled scalar field [HEAP]

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http://arxiv.org/abs/2211.03926


We present the general relativistic electrodynamics and magnetohydrodynamics with a helically coupled scalar field. We consider three component system with the fluid, scalar field and electromagnetic fields with the helical coupling. We derive three exact formulations: the covariant formulation, the ADM formulation, and the fully nonlinear and exact perturbation formulation. We also derive the weak-gravity limit with fully relativistic fluid and fields. The latter two formulations are presented in the cosmological context.

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J. Hwang and H. Noh
Wed, 9 Nov 22
39/76

Comments: 29 pages, no figure

Bootstrapping One-Loop Inflation Correlators with the Spectral Decomposition [CL]

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http://arxiv.org/abs/2211.03810


Phenomenological studies of cosmological collider physics in recent years have identified many 1-loop inflation correlators as leading channels for discovering heavy new particles around or above the inflation scale. However, complete analytical results for these massive 1-loop correlators are currently unavailable. In this work, we embark on a program of bootstrapping inflation correlators with massive exchanges at 1-loop order, with the input of tree-level inflation correlators and the techniques of spectral decomposition in dS. As a first step, we present for the first time the complete and analytical results for a class of 4-point and 3-point inflation correlators mediated by massive scalar fields at the 1-loop order. Using the full result, we provide simple and reliable analytical approximations for the signals and the background in the squeezed limit. We also identify configurations of the scalar trispectrum where the oscillatory signal from the loop is dominant over the background.

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Z. Xianyu and H. Zhang
Wed, 9 Nov 22
41/76

Comments: 65 pages

Black Holes as "Time Capsules": A Cosmological Graviton Background and the Hubble Tension [CEA]

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http://arxiv.org/abs/2211.03814


Minuscule primordial black holes before the end and after inflation can serve as “time capsules” bringing back energy from the past to a later epoch when they evaporate. As these black holes behave like matter, while the rest of the Universe content behaves like radiation, the mass fraction of these black holes, that is tiny at formation, becomes significant later. If sufficiently small, these black holes will evaporate while the Universe is still radiation dominated. We revisit this process and point out that gravitons produced during the evaporation behave as “dark radiation”. If the initial black holes are uniformly distributed so will be the gravitons and in this case they will be free of Silk damping and avoid current limits on “dark radiation” scenarios. Seeds for such black holes can arise during the last phases of inflation. We show here that with suitable parameters, this background graviton field can resolve the Hubble tension. We present current observational constraints on this scenario and suggest upcoming observational tests to prove or refute it. Finally, we also elaborate on the graviton background produced by particle annihilation during the Planck era or shortly after inflation.

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T. Piran and R. Jimenez
Wed, 9 Nov 22
53/76

Comments: Talk given by Tsvi Piran at the IWARA 2022 and RAGTIME24 conferences

Tilted non-spatially-flat inflation [CEA]

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http://arxiv.org/abs/2211.02999


We construct non-linear inflaton potential energy densities that describe not-necessarily very-slowly-rolling closed and open inflation models, and compute tilted primordial spatial inhomogeneity power spectra that follow from quantum mechanical fluctuations during inflation in these models. These tilted power spectra differ from those that have previously been used to study cosmological data in non-flat cosmological models.

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B. Ratra
Tue, 8 Nov 22
1/79

Comments: 14 pages

Bernstein spectral method for quasinormal modes of a generic black hole spacetime and application to instability of dilaton-de Sitter solution [CL]

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http://arxiv.org/abs/2211.02997


We present the improved Mathematica code which computes quasinormal frequencies with the help of the Bernstein spectral method for a general class of black holes, allowing for asymptotically flat, de Sitter or anti-de Sitter asymptotic. The method is especially efficient when searching for purely imaginary modes and here it is used for detecting the instability region of a charged scalar field in the background of the charged asymptotically de Sitter dilatonic black hole. We show that the instability has superradiant nature and the dilaton field essentially influences the region of instability.

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R. Konoplya and A. Zhidenko
Tue, 8 Nov 22
17/79

Comments: 8 pages, 2 figures, revtex

The CGF dark matter fluid [CL]

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http://arxiv.org/abs/2211.02881


The cosmological gauge field (CGF) is a classical solution of SU(2)-weak gauge theory oscillating rapidly in time. It is the dark matter driving the CGF cosmology. A general, local, mathematically natural construction of the CGF is given here. The macroscopic properties are derived. The CGF is an irrotational perfect fluid. It provides a synchronized global time coordinate and a global rest frame. There is a conserved number density. The energy density and pressure are related by the same equation of state as derived in the CGF cosmology and used in the TOV stellar structure equations for stars made of CGF dark matter. The present construction justifies the TOV solution. Some possible routes towards testing the theory are suggested at the end.

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D. Friedan
Tue, 8 Nov 22
20/79

Comments: 15 pages. Details of calculations are in a note in the ancillary files

Pulsar Timing Response to Gravitational Waves from a Massive Compact Source [HEAP]

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http://arxiv.org/abs/2211.03349


Pulsar timing arrays (PTAs) are searching for nanohertz-frequency gravitational waves (GWs) through cross-correlation of pulse arrival times from a set of radio pulsars. PTAs have relied upon a frequency-shift formula of the pulse, where planar GWs are usually assumed. Phase corrections due to the wavefront curvature have been recently discussed. In this paper, we derive a frequency-shift formula for GWs from a compact source such as a binary of supermassive black holes, where the differences in the GW amplitude and direction between the Earth and the pulsar are examined in the quadrupole approximation. By using the new formula, effects beyond the plane-wave approximation are discussed and nearby relevant GW source candidates are also mentioned.

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R. Kubo, K. Yamahira and H. Asada
Tue, 8 Nov 22
21/79

Comments: 4 pages, 2 figures, submitted to ApJL

Ruling Out Primordial Black Hole Formation From Single-Field Inflation [CL]

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http://arxiv.org/abs/2211.03395


The most widely studied formation mechanism of a primordial black hole (PBH) is collapse of large-amplitude perturbation on small scales generated in single-field inflation. In this Letter, we calculate one-loop correction to the large-scale power spectrum in such a model. We find models producing appreciable amount of PBHs generically induce too large one-loop correction on large scale probed by cosmic microwave background radiation. We therefore conclude that PBH formation from single-field inflation is ruled out.

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J. Kristiano and J. Yokoyama
Tue, 8 Nov 22
22/79

Comments: N/A

JWST high-z galaxies constraints on warm and cold dark matter models [CEA]

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http://arxiv.org/abs/2211.03620


We compare properties of high-redshift galaxies observed by JWST with hydrodynamical simulations, in the standard cold dark matter model and in warm dark matter models with a suppressed linear matter power spectrum. We find that current data are not in tension with cold dark matter nor with warm dark matter models with mWDM > 2 keV, since they probe bright and rare objects whose physical properties are similar in the different scenarios. We also show how two observables, the galaxy luminosity functions and the galaxy correlation function at small scales of faint objects, can be promising tools for discriminating between the different dark matter models.

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U. Maio and M. Viel
Tue, 8 Nov 22
29/79

Comments: N/A

Quantum gravity and scale symmetry in cosmology [CL]

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http://arxiv.org/abs/2211.03596


We discuss predictions for cosmology which result from the scaling solution of functional flow equations for a quantum field theory of gravity. A scaling solution is necessary to render quantum gravity renormalizable. Our scaling solution is directly connected to the quantum effective action for the metric coupled to a scalar field. It includes all effects of quantum fluctuations and is invariant under general coordinate transformations. Solving the cosmological field equations derived by variation of the quantum effective action provides for a detailed quantitative description of the evolution of the universe. The \qq{beginning state} of the universe is found close to an ultraviolet fixed point of the flow equation. It can be described by an inflationary epoch, with approximate scale invariance of the observed primordial fluctuation spectrum explained by approximate quantum scale symmetry. Overall cosmology realizes a dynamical crossover from the ultraviolet fixed point to an infrared fixed point which is approached in the infinite future. Present cosmology is close to the infrared fixed point. It features dynamical dark energy mediated by a light scalar field. The tiny mass of this cosmon arises from its role as a pseudo Goldstone boson of spontaneously broken quantum scale symmetry. The extremely small value of the present dark energy density in Planck units results dynamically as a consequence of the huge age of the universe. The cosmological constant problem finds a dynamical solution. We present a detailed quantitative computation of the scaling solution for the scalar effective potential and the field-dependent coefficient of the curvature scalar. This allows for further quantitative predictions.

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C. Wetterich
Tue, 8 Nov 22
41/79

Comments: 31 pages, 2 figures

Brane cosmology with variable tension [CL]

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http://arxiv.org/abs/2211.02737


We study brane-world models and demonstrate that such models do not admit self-similar solutions through the matter collineation approach. By introducing the hypothesis of variable brane tension, $\lambda,$ we outline the new effective field equation (EFE) in the most simple case (symmetric embedding) under the assumption that the fundamental constants in 5D are constants. In this case, we find the exact form that each physical quantity may take in order that the EFE become invariant under scale transformations. By taking into account such assumptions, we find that in 4D, the gravitational constant $\kappa^{2}\thicksim\lambda$ while the cosmological constant $\Lambda\thicksim\lambda^{2}$ are always decreasing. These results are quite general and valid for any homogeneous self-similar metric. Nevertheless, the study of the EFE under scale symmetries suggests that $\rho\thicksim\lambda$ (as a functional relationship). This allows to get a growing $\kappa^{2}$ but, in this case, the fundamental constants in 5D must vary as well. We outline a toy model allowing such a possibility.

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J. Belinchón and S. Dib
Tue, 8 Nov 22
77/79

Comments: Accepted to Canadian Journal of Physics

Cosmological axion in post-Newtonian approximation [CL]

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http://arxiv.org/abs/2211.02197


We present first-order post-Newtonian (1PN) approximations of a general imperfect fluid and of an axion as a coherently oscillating massive scalar field, both in the cosmological context. For the axion, using the Klein transformation and Madelung transformation we derive the Schr\”odinger and Madelung hydrodynamic formulations, respectively, in exact covariant way and to 1PN order. Complete sets of equations for the 1PN formulations are derived without fixing the temporal gauge condition. We study the linear instability in cosmology and a static limit for both fluid and axion; these are presented independently of the gauge condition to 1PN order, thus are naturally gauge-invariant.

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J. Hwang and H. Noh
Mon, 7 Nov 22
24/67

Comments: 18 pages, no figure

Cosmic Topology I: Limits on Orientable Euclidean Manifolds from Circle Searches [CEA]

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http://arxiv.org/abs/2211.02603


The Einstein field equations of general relativity constrain the local curvature at every point in spacetime, but say nothing about the global topology of the Universe. Cosmic microwave background anisotropies have proven to be the most powerful probe of non-trivial topology since, within $\Lambda$CDM, these anisotropies have well-characterized statistical properties, the signal is principally from a thin spherical shell centered on the observer (the last scattering surface), and space-based observations nearly cover the full sky. The most generic signature of cosmic topology in the microwave background is pairs of circles with matching temperature and polarization patterns. No such circle pairs have been seen above noise in the WMAP or Planck temperature data, implying that the shortest non-contractible loop around the Universe through our location is longer than 98.5% of the comoving diameter of the last scattering surface. We translate this generic constraint into limits on the parameters that characterize manifolds with each of the nine possible non-trivial orientable Euclidean topologies, and provide a code which computes these constraints. In all but the simplest cases, the shortest non-contractible loop in the space can be shorter than the diameter of the last scattering surface by a factor ranging from 2 to at least 6. This result implies that a broader range of manifolds is observationally allowed than widely appreciated. Probing these manifolds will require subtler statistical signatures such as off-diagonal correlations of harmonic coefficients.

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P. Petersen, Y. Akrami, C. Copi, et. al.
Mon, 7 Nov 22
26/67

Comments: 14 pages, 7 figures

Post-inflationary GW production in generic higher (infinite) derivative gravity [CL]

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http://arxiv.org/abs/2211.02070


Gravity can be embedded into a renormalizable theory by means of adding quadratic in curvature terms. However, this at first leads to the presence of the Weyl ghost. It is possible to get rid of this ghost if the locality assumption is weakened and the propagator of the graviton is represented by an entire function of the d’Alembertian operator without new poles and zeros. Models of this type admit a cosmological solution describing the $R^2$, or Starobinsky, inflation. We study graviton production after inflation in this model and show that it is negligible despite the presence of the higher derivative operators which could potentially cause instabilities.

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A. Koshelev, A. Starobinsky and A. Tokareva
Mon, 7 Nov 22
33/67

Comments: We dedicate this paper to the memory of Valery Rubakov

Asymptotically flat vacuum solution for a rotating black hole in a modified gravity theory [CL]

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http://arxiv.org/abs/2203.07690


The theory of f(R)-gravity is one of the theories of modified Einstein gravity. The vacuum solution, on the other hand, of the field equation is the solution for black hole geometry. We establish here an asymptotically flat rotating black hole solution in an f(R)-gravity. This essentially leads to the modified solution to the Kerr black hole. This solution exhibits the change in fundamental properties of the black hole and its geometry. It particularly shows that radii of marginally stable and bound orbits and black hole event horizon increase compared to those in Einstein gravity, depending on the modified gravity parameter. It further argues for faster spinning black holes with spin (Kerr) parameter greater than unity, without any naked singularity. This supports the weak cosmic censorship hypothesis.

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A. Das and B. Mukhopadhyay
Mon, 7 Nov 22
41/67

Comments: 12 pages including 6 figures and 2 tables; some typos corrected; version published in European Physical Journal C (EPJC)

Impact of multiple modes on the evolution of self-interacting axion condensate around rotating black holes [CL]

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http://arxiv.org/abs/2211.01949


Ultra-light particles, such as axions, form a macroscopic condensate around a highly spinning black hole by the superradiant instability. Due to its macroscopic nature, the condensate opens the possibility of detecting the axion through gravitational wave observations. However, the precise evolution of the condensate must be known for the actual detection. For future observation, we numerically study the influence of the self-interaction, especially interaction between different modes, on the evolution of the condensate in detail. First, we focus on the case when condensate starts with the smallest possible angular quantum number. For this case, we perform the non-linear calculation and show that the dissipation induced by the mode interaction is strong enough to saturate the superradiant instability, even if the secondary cloud starts with quantum fluctuations. Our result indicates that explosive phenomena such as bosenova do not occur in this case. We also show that the condensate settles to a quasi-stationary state mainly composed of two modes, one with the smallest angular quantum number for which the superradiant instability occurs and the other with the adjacent higher angular quantum number. We also study the case when the condensate starts with the dominance of the higher angular quantum number. We show that the dissipation process induced by the mode coupling does not occur for small gravitational coupling. Therefore, bosenova might occur in this case.

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H. Omiya, T. Takahashi, T. Tanaka, et. al.
Fri, 4 Nov 22
4/84

Comments: 29 pages, 25 figures, 1 table

Scalarization [CL]

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http://arxiv.org/abs/2211.01766


Scalarization is a mechanism that endows strongly self-gravitating bodies, such as neutron stars and black holes, with a scalar field configuration. It resembles a phase transition in that the scalar configuration only appears when a certain quantity that characterizes the compact object, e.g., its compactness or spin, is beyond a threshold. We provide a critical and comprehensive review of scalarization, including the mechanism itself, theories that exhibit it, its manifestation in neutron stars, black holes, and their binaries, potential extension to other fields, and a thorough discussion of future perspectives.

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D. Doneva, F. Ramazanoğlu, H. Silva, et. al.
Fri, 4 Nov 22
27/84

Comments: 50 pages, 24 figures. Review commissioned by Reviews of Modern Physics, submitted version, comments welcome

On the superstring-inspired quantum correction to the Starobinsky model of inflation [CL]

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http://arxiv.org/abs/2211.01546


Superstring/M-theory is the theory of quantum gravity that can provide the UV-completion to viable inflation models. We modify the Starobinsky inflation model by adding the Bel-Robinson tensor $T^{\mu\nu\lambda\rho}$ squared term proposed as the leading quantum correction inspired by superstring theory. The $(R+\frac{1}{6m^2}R^2 -\frac{\beta}{8m^6}T^2)$ model under consideration has two parameters: the inflaton mass $m$ and the string-inspired positive parameter $\beta$. We derive the equations of motion in the Friedmann-Lemaitre-Robertson-Walker universe and investigate its solutions. We find the physical bounds on the value of the parameter $\beta$ by demanding the absence of ghosts and consistency of the derived inflationary observables with the measurements of the cosmic microwave background radiation.

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S. Ketov, E. Pozdeeva and S. Vernov
Fri, 4 Nov 22
55/84

Comments: 22 pages, 5 figures, LaTeX

Black hole perturbations in modified gravity theories [CL]

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http://arxiv.org/abs/2211.01103


The recent first detection of gravitational waves (GWs) from binary black hole mergers has spurred a renewed interest in possible deviations from General Relativity (GR), since they could be detected in the GWs emitted by such systems. Of particular interest is the ringdown phase of a binary black hole merger, which can be described by linear perturbations about a background stationary black hole solution. These perturbations mainly correspond to a superposition of ‘quasi-normal modes’ (QNMs), whose frequencies form a discrete set. One expects that modified gravity models could predict QNMs that differ from their GR counterpart: the detailed analysis of the GW signal represents an invaluable window to test GR and to look for specific signatures of modified gravity.
The work done in this thesis takes place in the context of scalar-tensor theories of gravity, and more particularly the Degenerate Higher-Order Scalar-Tensor theories. We start by a review of these theories and their properties, and describe a way to reformulate them in a framework with a clear geometrical interpretation. We then study linear perturbations about several existing nonrotating black hole solutions of such theories, and show why the perturbation equations obtained are very hard to decouple in general. When it is possible, in the case of odd parity perturbations, we describe the propagation of waves and relate it to the stability of the underlying spacetime. When it is not, we circumvent the difficulty by making use of an algorithm proposed recently in the mathematical literature that allows us to decouple the equations both at the black hole horizon and at infinity. This allows us to get the asymptotic behaviour of waves on such spacetimes, yielding valuable information that can allow us to rule some of them out. Finally, we use the asymptotic behaviours obtained to compute QNMs numerically.

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H. Roussille
Thu, 3 Nov 22
4/59

Comments: PhD thesis (defended 17/06/2022, Universit\’e Paris Cit\’e), 267 pages, 17 figures, 1 appendix, short introduction in French. Based on arXiv:2012.10218, arXiv:2103.14744, arXiv:2103.14750, arXiv:2204.04107, arXiv:2205.07746

Regular black holes sourced by nonlinear electrodynamics [CL]

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http://arxiv.org/abs/2211.00743


The paper is a brief review on the existence and basic properties of static, spherically symmetric regular black hole solutions of general relativity, where the source of gravity is represented by nonlinear electromagnetic fields with the Lagrangian function $L$ depending on the single invariant $f = F_{\mu\nu}F^{\mu\nu}$ or on two variables: either $L(f, h)$, where $h = {^}F_{\mu\nu} F^{\mu\nu}$, where ${^}F_{\mu\nu}$ is the Hodge dual of $F_{\mu\nu}$, or $L(f, J)$, where $J = F_{\mu\nu}F^{\nu\rho} F_{\rho\sigma} F^{\sigma\mu}$. A number of no-go theorems are discussed, revealing the conditions under which the space-time cannot have a regular center, among which the theorems concerning $L(f,J)$ theories are probably new. These results concern both regular black holes and regular particlelike or starlike objects (solitons) without horizons. Thus, a regular center in solutions with an electric charge $q_e\ne 0$ is only possible with nonlinear electrodynamics (NED) having no Maxwell weak field limit. Regular solutions with $L(f)$ and $L(f, J)$ NED, possessing a correct (Maxwell) weak-field limit, are possible if the system contains only a magnetic charge $q_m \ne 0$. It is shown, however, that in such solutions the causality and unitarity as well as dynamic stability conditions are inevitably violated in a neighborhood of the center. Some particular examples are discussed.

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K. Bronnikov
Thu, 3 Nov 22
36/59

Comments: 30 pages, 4 figures. Invited chapter for the edited book “Regular Black Holes: Towards a New Paradigm of the Gravitational Collapse” (Ed. C. Bambi, Springer Singapore, expected in 2023)

Primordial non-Gaussianity from Galilean Genesis without strong coupling problem [CL]

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http://arxiv.org/abs/2211.00388


Galilean Genesis is generically plagued with a strong coupling problem, but this can be avoided depending on the hierarchy between a classical energy scale of genesis and a strong coupling scale. In this paper, we investigate whether or not the models of Galilean Genesis without the strong coupling problem can explain the statistical properties of the observed CMB fluctuations based on two unified frameworks of Galilean Genesis. By focusing on the class in which the propagation speeds of the scalar and tensor perturbations are constant, we show that the models avoiding strong coupling and allowing a slightly red-tilted scalar power spectrum suffer from an overproduction of a scalar non-Gaussianity.

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S. Akama and S. Hirano
Wed, 2 Nov 22
7/67

Comments: 16 pages, 1 figure

White Dwarfs in Dwarf Spheroidal Galaxies: A New Class of Compact-Dark-Matter Detectors [CEA]

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http://arxiv.org/abs/2211.00013


Recent surveys have discovered a population of faint supernovae, known as Ca-rich gap transients, inferred to originate from explosive ignitions of white dwarfs. In addition to their unique spectra and luminosities, these supernovae have an unusual spatial distribution and are predominantly found at large distances from their presumed host galaxies. We show that the locations of Ca-rich gap transients are well matched to the distribution of dwarf spheroidal galaxies surrounding large galaxies, in accordance with a scenario where dark matter interactions induce thermonuclear explosions among low-mass white dwarfs that may be otherwise difficult to ignite with standard stellar or binary evolution mechanisms. A plausible candidate to explain the observed event rate are primordial black holes with masses above $10^{21}$ grams.

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J. Smirnov, A. Goobar, T. Linden, et. al.
Wed, 2 Nov 22
10/67

Comments: 5 pages, 4 figures, one appendix

Dark Energy as a Post-Inflation Effect in Quadratic Gravity [CL]

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http://arxiv.org/abs/2211.00491


We analytically and numerically show that the acceleration of the cosmic expansion could be explained by a Quadratic Gravity model which is known to be able to trigger sufficient inflation, with neither negative pressure matter nor cosmological constant. Accordingly, it suggests that the Dark Energy could possibly be a post-inflation effect in Quadratic Gravity. We also show that this model admits all Einstein metrics as its solutions. Consequently, classic tests of Einstein’s Gravity cannot falsify this model.

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H. Chang
Wed, 2 Nov 22
51/67

Comments: 16 pages, 3 figures

Shadow of black hole surrounded by magnetized plasma: Axion-plasmon cloud [CL]

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http://arxiv.org/abs/2211.00300


By exploiting the extreme environment of the black hole (BH) as a potential place for axion-photon interaction, we use an axion-producing model of the magnetized plasma to study the shadow of an asymptotically flat rotating BH immersed into an axion-plasmon cloud. By aiming to reveal footprints of axion in the dark shadow of BH, we in this paper explore the influence of the fixed axion-plasmon background on the motion of incident photons around the rotating BH. Under some free parameter settings, we find that axion-plasmon cloud around rotating BH affects the shape and size of the shadow in such a way that its role is distinguishable from non-magnetized plasma and standard vacuum solutions. By being limited to high rotation BH, we show that the size of the BH shadow increases as the axion-plasmon coupling gets strong. Interestingly, our analysis indicates that as the mass of axion gets heavier, it can leave a subtle imprint of itself on the shadow. Conversely, in the non-rotating limit (Schwarzschild), by recovering the spherical symmetry of the shadow shape of BH, its size decreases. In coordination with the trend of change in shadow size, the investigation of the energy emission from the BH surrounded by the magnetized plasma shows that the maximal energy emission rate from the rotating BH in the presence of axion-plasmon cloud increases compared to the non-magnetized plasma and the vacuum solutions. Subsequently, by relaxing the rotation, the axion-plasmon cloud causes a decrease in the energy emission rate from the BH.

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M. Khodadi
Wed, 2 Nov 22
58/67

Comments: 23 pages, 15 figures, for publication in ” Nuclear Physics B”

Primordial Black Hole Mass Function with Mass Gap [CEA]

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http://arxiv.org/abs/2210.16479


In this paper, we investigate the primordial black hole (PBH) mass function with mass gap. Firstly, to obtain a data-supported PBH mass function with mass gap for subsolar masses PBHs, we fine-tune the coefficients of a model-independent power spectrum of primordial curvature perturbations. Then we take this unique PBH mass function into consideration and calculate the energy density spectrum of the stochastic gravitational wave background from PBH mergers. We find the location of its first peak almost has no relationship with the mass gap and is only determined by the probability distribution of frequencies at which PBH binaries merge. Apart from the first peak, there must be an accompanying smaller trough at higher frequency resulting from the mass gap. Therefore, the detection of this smaller trough will provide more information about inflation and PBH formation.

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X. Bi, L. Chen and K. Wang
Tue, 1 Nov 22
1/100

Comments: 8 pages, 4 figures

Formalizing Anisotropic Inflation in Modified Gravity [CL]

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http://arxiv.org/abs/2210.16383


Motivated by the fact that the pre-inflationary era may evolve in an exotic way, in this work we formalize anisotropic evolution in the context of modified gravity, focusing on pre-inflationary and near the vicinity of the inflationary epochs. We specialize on specific metrics like Bianchi and Taub and we formalize the inflationary theory in vacuum $F(R)$ gravity, in $F(R)$ gravity with an extra scalar field and in Gauss-Bonnet gravity. We discuss the qualitative effects of the anisotropies on the evolution of the Universe and also we consider several specific solutions, like the de Sitter solution, in both the isotropic and anisotropic contexts. Furthermore, several exotic modified gravity cosmological solutions, like the ones which contain finite time singularities, are also discussed in brief.

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S. Nojiri, S. Odintsov, V. Oikonomou, et. al.
Tue, 1 Nov 22
17/100

Comments: NPB Accepted

Cosmology in theories with spontaneous scalarization of neutron stars [CL]

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http://arxiv.org/abs/2210.16983


In a model of spontaneous scalarization of neutron stars proposed by Damour and Esposite-Farese, a general relativistic branch becomes unstable to trigger tachyonic growth of a scalar field $\phi$ toward a scalarized branch. Applying this scenario to cosmology, there is fatal tachyonic instability of $\phi$ during inflation and matter dominance being incompatible with solar-system constraints on today’s field value $\phi_0$. In the presence of a four-point coupling $g^2 \phi^2 \chi^2/2$ between $\phi$ and an inflaton field $\chi$, it was argued by Anson et al. that a positive mass squared heavier than the square of a Hubble expansion rate leads to the exponential suppression of $\phi$ during inflation and that $\phi_0$ can remain small even with the growth of $\phi$ after the radiation-dominated epoch. For several inflaton potentials approximated as $V(\chi)=m^2 \chi^2/2$ about the potential minimum, we study the dynamics of $\phi$ during reheating as well as other cosmological epochs in detail. For certain ranges of the coupling $g$, the homogeneous field $\phi$ can be amplified by parametric resonance during a coherent oscillation of the inflaton. Incorporating the backreaction of created particles under a Hartree approximation, the maximum values of $\phi$ reached during preheating are significantly smaller than those obtained without the backreaction. We also find that the minimum values of $g$ consistent with solar system bounds on $\phi$ at the end of reheating are of order $10^{-5}$ and hence there is a wide range of acceptable values of $g$. Thus, the scenario proposed by Anson et al. naturally leads to the viable cosmological evolution of $\phi$ consistent with local gravity constraints, without modifying the property of scalarized neutron stars.

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R. Nakarachinda, S. Panpanich, S. Tsujikawa, et. al.
Tue, 1 Nov 22
20/100

Comments: 15 pages, 8 figures

Thick branes via higher order field theory models with exponential and power-law tails [CL]

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http://arxiv.org/abs/2210.17387


In this work, we obtain exact thick brane models in $4+1$ dimensions generated by higher order field theory kinks, inspired by specific potentials for $\phi^{10}$ and $\phi^{18}$ models. We verify that the geodesic equation along the fifth dimension confirms the confining effects of the scalar field on the brane for all of these models. These models provide new solutions with exponential and power-law tails which live in different topological sectors. We show that the resulting branes of specific exponential law models do not possess $Z_2$-symmetry. Furthermore, we examine the stability of the thick branes, by determining the sign of the $w^2$ term in the expansion of the potential for the resulting Schr\”{o}dinger-like equation. It turns out that two of the three models of the $\phi^{10}$ brane are stable, while another contains unstable modes for certain ranges of the model parameters. We also show that the brane solution from the specific $\phi^{18}$ models are stable, while the others involve neutral equilibrium. The asymptotic behaviour of the brane solutions are also discussed.

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M. Peyravi, S. Nazifkar, F. Lobo, et. al.
Tue, 1 Nov 22
27/100

Comments: 23 pages, 10 figures. arXiv admin note: text overlap with arXiv:1504.04603

Colliding Ghosts: Constraining Inflation with the Parity-Odd Galaxy Four-Point Function [CEA]

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http://arxiv.org/abs/2210.16320


Could new physics break the mirror symmetry of the Universe? Utilizing recent measurements of the parity-odd four-point correlation function of BOSS galaxies, we probe the physics of inflation by placing constraints on the amplitude of a number of parity-violating models. Within canonical models of (single-field, slow-roll) inflation, no parity-asymmetry can occur; however, it has recently been shown that breaking of the standard assumptions can lead to parity violation within the Effective Field Theory of Inflation (EFTI). In particular, we consider the Ghost Condensate and Cosmological Collider scenarios – the former for the leading and subleading operators in the EFTI and the latter for different values of mass and speed of an exchanged spin-$1$ particle – for a total of $18$ models. Each instance yields a definite prediction for the inflationary trispectrum, which we convert to a late-time galaxy correlator prediction (through a highly non-trivial calculation) and constrain using the observed data. We find no evidence for inflationary parity-violation (with each of the $18$ models having significances below $2.4\sigma$), and place the first constraints on the relevant coupling strengths, at a level comparable with the theoretical perturbativity bounds. This is also the first time Cosmological Collider signatures have directly been searched for in observational data. We further show that possible secondary parity-violating signatures in galaxy clustering can be systematically described within the Effective Field Theory of Large-Scale Structure. We argue that these late-time contributions are subdominant compared to the primordial parity-odd signal for a vast region of parameter space. In summary, the results of this paper disfavor the notion that the recent hints of parity-violation observed in the distribution of galaxies are due to new physics.

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G. Cabass, M. Ivanov and O. Philcox
Tue, 1 Nov 22
40/100

Comments: 20+8 spooky pages, 4 figures, submitted to Phys. Rev. D. Code available at this https URL

The CMSSM Survives Planck, the LHC, LUX-ZEPLIN, Fermi-LAT, H.E.S.S. and IceCube [CL]

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http://arxiv.org/abs/2210.16337


We revisit the viability of the CMSSM, searching for regions of parameter space that yield a neutralino dark matter density compatible with Planck measurements, as well as LHC constraints including sparticle searches and the mass of the Higgs boson, recent direct limits on spin-independent and -dependent dark matter scattering from the LUX-ZEPLIN (LZ) experiment, the indirect constraints from Fermi-LAT and H.E.S.S. on dark matter annihilations to photons in dwarf spheroidal galaxies and the Galactic Centre, and the IceCube limits on muons from annihilations to neutrinos in the Sun. For representative values of $\tan \beta$ and $A_0$ we map in detail the Planck-compatible strips in CMSSM parameter planes, which exhibit multiple distinctive features for large $\tan \beta$, $A_0 = 0$ and $\mu > 0$, and identify portions of the strips that survive all the phenomenological constraints. We find that the most powerful constraint is that from $m_h$, followed by the LZ limit on spin-independent scattering, whereas sparticle searches at the LHC and indirect dark matter searches are less restrictive. Most of the surviving CMSSM parameter space features a Higgsino-like dark matter particle with a mass $\sim 1000-1100$ GeV, which could best be probed with future direct searches for dark matter scattering.

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J. Ellis, K. Olive, V. Spanos, et. al.
Tue, 1 Nov 22
41/100

Comments: 40 pages, 18 figures

Non-Gaussianities in generalized non-local $R^2$-like inflation [CL]

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http://arxiv.org/abs/2210.16459


In [1], a most general higher curvature non-local gravity action admitting $R^2$-like inflationary solution predicting scalar spectral index $n_s(N)\approx 1-\frac{2}{N}$, where $N$ is the number of e-folds before the end of inflation, $N\gg 1$, any value of the tensor-to-scalar ratio $r(N)<0.036$ and tensor tilt $n_t(N)$ violating the $r= -8n_t$ condition was obtained. In this paper, we compute scalar primordial non-Gaussianities (PNGs) in this theory and effectively demonstrate that higher curvature non-local terms lead to new shapes of reduced bispectrum $f_{\rm NL}\left( k_1,\,k_2,\,k_3 \right)$ mimicking several classes of scalar field models of inflation known in the literature. We obtain $\vert f_{\rm NL}\vert \sim O(1-10)$ in the equilateral, orthogonal, and squeezed limits and the running of PNGs measured by the quantity $\vert\frac{d\ln f_{\rm NL}}{d\ln k}\vert\lesssim 1$. We project these results in the scope of future CMB, Large Scale Structure observations to probe the nature of quantum gravity. Furthermore, we demonstrate that $R^2$-like inflation in non-local modification of gravity brings a paradigm shift in our understanding of early Universe cosmology through non-trivial predictions which go beyond the current status of effective field theories (EFTs) of single field, quasi-single field, and multiple field inflation. In summary, through our generalized non-local $R^2$-like inflation, we obtain for the first time a robust geometric framework of inflation that can explain any detection of observable quantities related to scalar PNGs.

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A. Koshelev, K. Kumar and A. Starobinsky
Tue, 1 Nov 22
80/100

Comments: 30 pages, 7 figures

Soft theorems for boosts and other time symmetries [CL]

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http://arxiv.org/abs/2210.16276


We derive soft theorems for theories in which time symmetries — symmetries that involve the transformation of time, an example of which are Lorentz boosts — are spontaneously broken. The soft theorems involve unequal-time correlation functions with the insertion of a soft Goldstone in the far past. Explicit checks are provided for several examples, including the effective theory of a relativistic superfluid and the effective field theory of inflation. We discuss how in certain cases these unequal-time identities capture information at the level of observables that cannot be seen purely in terms of equal-time correlators of the field alone. We also discuss when it is possible to phrase these soft theorems as identities involving equal-time correlators.

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L. Hui, A. Joyce, I. Komissarov, et. al.
Mon, 31 Oct 22
4/60

Comments: 50 pages

Outlook for detecting the gravitational wave displacement and spin memory effects with current and future gravitational wave detectors [CL]

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http://arxiv.org/abs/2210.16266


Gravitational wave memory effects arise from non-oscillatory components of gravitational wave signals, and they are predictions of general relativity in the nonlinear regime that have close connections to the asymptotic properties of isolated gravitating systems. There are many types of memory effects that have been studied in the literature. In this paper we focus on the “displacement” and “spin” memories, which are expected to be the largest of these effects from sources such as the binary black hole mergers which have already been detected by LIGO and Virgo. The displacement memory is a change in the relative separation of two initially comoving observers due to a burst of gravitational waves, whereas the spin memory is a portion of the change in relative separation of observers with initial relative velocity. As both of these effects are small, LIGO, Virgo, and KAGRA can only detect memory effects from individual events that are much louder (and thus rarer) than those that have been detected so far. By combining data from multiple events, however, these effects could be detected in a population of binary mergers. In this paper, we present new forecasts for how long current and future detectors will need to operate in order to measure these effects from populations of binary black hole systems that are consistent with the populations inferred from the detections from LIGO and Virgo’s first three observing runs. We find that a second-generation detector network of LIGO, Virgo, and KAGRA operating at the O4 (“design”) sensitivity for 1.5 years and then operating at the O5 (“plus”) sensitivity for an additional year can detect the displacement memory. For Cosmic Explorer, we find that displacement memory could be detected for individual loud events, and that the spin memory could be detected in a population after 5 years of observation time.

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A. Grant and D. Nichols
Mon, 31 Oct 22
10/60

Comments: 17+7 pages, 7 figures

Resolving the Hubble tension with Early Dark Energy [CEA]

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http://arxiv.org/abs/2210.16296


Early dark energy (EDE) offers a solution to the so-called Hubble tension. Recently, it was shown that the constraints on EDE using Markov Chain Monte Carlo are affected by prior volume effects. The goal of this paper is to present constraints on the fraction of EDE, $f_\mathrm{EDE}$, and the Hubble parameter, $H_0$, which are not subject to prior volume effects. We conduct a frequentist profile likelihood analysis considering Planck cosmic microwave background, BOSS full-shape galaxy clustering, DES weak lensing, and SH0ES supernova data. Contrary to previous findings, we find that $H_0$ for the EDE model is in statistical agreement with the SH0ES direct measurement at $\leq 1.7\,\sigma$ for all data sets. For our baseline data set (Planck + BOSS), we obtain $f_\mathrm{EDE} = 0.087\pm 0.037$ and $H_0 = 70.57 \pm 1.36\, \mathrm{km/s/Mpc}$ at $68\%$ confidence limit. We conclude that EDE is a viable solution to the Hubble tension.

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L. Herold and E. Ferreira
Mon, 31 Oct 22
24/60

Comments: 6 pages, 3 figures, 1 table

Dark matter freeze-in produces large post-inflationary isocurvature [CEA]

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http://arxiv.org/abs/2210.15691


In this Letter, we show that the nonthermal nature of dark matter freeze-in production leads to large, totally correlated dark matter-photon isocurvature perturbations, which are imprinted in anisotropies of the cosmic microwave background (CMB). Isocurvature is typically expected from inflationary physics, but the isocurvature from freeze-in arises post inflation. We compute the freeze-in of millicharged dark matter, generated from electron-positron annihilations in the early Universe. We find that current CMB observations from \textit{Planck} exclude this scenario for dark matter masses between 1 MeV and 10 GeV at more than $2\sigma$, whereas upcoming CMB experiments will have the sensitivity to reach at least the $4\sigma$ level. We anticipate any scenario in which dark matter is nonthermally produced to generically give rise to isocurvature. Our work opens a new avenue for exploring fundamental dark matter physics through its impact on cosmological observables.

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N. Bellomo, K. Berghaus and K. Boddy
Mon, 31 Oct 22
38/60

Comments: 8 pages, 3 figures

Cosmological inference from the EFTofLSS: the eBOSS QSO full-shape analysis [CEA]

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http://arxiv.org/abs/2210.14931


We present cosmological results inferred from the effective-field theory (EFT) analysis of the full-shape of eBOSS quasars (QSO) power spectrum. We validate our analysis pipeline against simulations, and find overall good agreement between the analyses in Fourier and configuration space. Keeping the baryon abundance and the spectral tilt fixed, we reconstruct at $68\%$ CL the fractional matter abundance $\Omega_m$, the reduced Hubble constant $h$, and the clustering amplitude $\sigma_8$, to respectively $\Omega_m=0.327\pm 0.035$, $h=0.655\pm 0.034$, and $\sigma_8=0.880\pm 0.083$ from eBOSS QSO alone. These constraints are consistent at $\lesssim 1.8\sigma$ with the ones from Planck and from the EFT analysis of BOSS full-shape. Interestingly $S_8$ reconstructed from eBOSS QSO is slightly higher than that deduced from Planck and BOSS, although statistically consistent. In combination with the EFT likelihood of BOSS, supernovae from Pantheon, and BAO from lyman-$\alpha$ and 6dF/MGS, constraints improve to $\Omega_m = 0.2985\pm 0.0069$ and $h = 0.6803\pm 0.0075$, in agreement with Planck and with similar precision. We also explore one-parameter extensions to $\Lambda$CDM and find that results are consistent with flat $\Lambda$CDM at $\lesssim 1.1\sigma$. We obtain competitive constraints on the curvature density fraction $\Omega_k=-0.039\pm 0.029$, the dark energy equation of state $w_0=-1.038\pm 0.041$, the effective number of relativistic species $N_{\rm eff}=3.44^{+0.44}{-0.91}$ at $68\%$ CL, and the sum of neutrino masses $\sum m\nu<0.274e$V at $95\%$ CL, without Planck data. Including Planck data, contraints significantly improve thanks to the large lever arm in redshift between LSS and CMB measurements. In particular, we obtain the stringent constraint $\sum m_\nu<0.093e$V, competitive with recent lyman-$\alpha$ forest power spectrum bound.

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T. Simon, P. Zhang and V. Poulin
Fri, 28 Oct 22
15/56

Comments: 33 + 13 pages, 8 figures. Comments welcome!

Renormalization Group for Non-minimal $φ^2 R$ Couplings and Gravitational Contact Interactions [CL]

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http://arxiv.org/abs/2210.15640


Theories of scalars and gravity, with an Einstein-Hilbert term and non-minimal interactions, $M^2R/2 -\alpha\phi^2R/12 $, have graviton exchange induced contact interactions. These modify the renormalization group, leading to a discrepancy between the conventional calculations in the Jordan frame that ignore this effect (and are found to be incorrect), and the Einstein frame in which $\alpha$ does not exist. Thus, the calculation of quantum effects in the Jordan and Einstein frames does not generally commute with the transition from the Jordan to the Einstein frame. In the Einstein frame, though $\alpha$ is absent, for small steps in scale $\delta\mu/\mu$ infinitesimal contact terms $\sim \delta\alpha$ are induced, that are then absorbed back into other couplings by the contact terms. This modifies the $\beta$-functions in the Einstein frame. We show how correct results can be obtained in a simple model by including this effect.

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D. Ghilencea and C. Hill
Fri, 28 Oct 22
18/56

Comments: 11 pages, 4 figures. arXiv admin note: text overlap with arXiv:2009.14782

Solvable potentials in a FLRW+Scalar universe and Fits to type Ia supernovae data [CL]

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http://arxiv.org/abs/2210.15475


FLRW equations are analyzed in a universe with a cosmic scalar background that is spatially uniform but time-varying. Some solvable scalar potentials to the combined dynamics in such a universe are presented. They are consistent with the scalar dynamics as a consequence of energy momentum conservation. Certain potentials are found to provide very good fits to type Ia supernovae data, with the kinetic and potential energies of the scalar providing the source for dark matter and dark energy. The scalar rolls down the potential as the universe expands, with the potential playing the role of a time-varying cosmological constant, modeling a scenario recently discussed in the literature.

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B. Balakrishna
Fri, 28 Oct 22
23/56

Comments: N/A

(Slow-)Twisting inflationary attractors [CL]

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http://arxiv.org/abs/2210.14900


We explore the dynamics of multi-field inflationary models with more than two fields. We first revisit the two-field case where the attractor solution with either small or large turn rate can be found analytically. For three fields in the slow-roll, slow-twist and extreme turning regime we provide elegant expressions for the attractor solution for generic field-space geometries and potentials and study the behaviour of first order perturbations. For generic $\mathcal{N}$-field models, our method quickly grows in algebraic complexity. We observe that field-space isometries are common in the literature and we are able to obtain the attractor solutions and deduce stability for some isometry classes of $\mathcal{N}$-field models. Finally, we apply our discussion to concrete supergravity models. These analyses conclusively demonstrate the existence of $\mathcal{N}>2$ dynamical attractors distinct from the two-field case, and provide tools useful for future studies of their phenomenology in the cosmic microwave background and stochastic gravitational wave spectrum.

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P. Christodoulidis and R. Rosati
Thu, 27 Oct 22
15/55

Comments: 34 pages, 9 figures. Comments welcome

Quasinormal modes in higher derivative gravity: testing the black hole parametrization and sensitivity of overtones [CL]

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http://arxiv.org/abs/2210.14506


The fundamental quasinormal modes of black holes in higher derivative gravity given by the Einstein-Weyl action are known to be moderately corrected by the Weyl term. Here we will show that the first several overtones are highly sensitive to even a relatively small Weyl correction, which might be important when representing the earlier stage of the black-hole ringdown. In addition, we have solved the problem related to analytical parametrized approximation of the numerical black hole solution in the Einstein-Weyl theory: In some range of parameters the approximation for the metric developed up to the third order lead to the unusual highly non-monotonic behavior of the frequencies. We have shown that this problem can be solved via the extension of the parametrization of the metric to higher orders until reaching the regime when the frequencies do not change with further increasing of the order.

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R. Konoplya
Thu, 27 Oct 22
40/55

Comments: 7 pages, 3 figures, 2 tables, revtex

Gravitational Waves and Primordial Black Hole Productions from Gluodynamics [CL]

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http://arxiv.org/abs/2210.14094


We construct a holographic model describing the gluon sector of Yang-Mills theories at finite temperature in the non-perturbative regime. The equation of state as a function of temperature is in good accordance with the lattice quantum chromodynamics (QCD) data. Moreover, the Polyakov loop and the gluon condensation, which are proper order parameters to capture the deconfinement phase transition, also agree quantitatively well with the lattice QCD data. We obtain a strong first-order confinement/deconfinement phase transition at $T_c=276.5\,\text{MeV}$ that is consistent with the lattice QCD prediction. The resulting stochastic gravitational-wave backgrounds from this confinement/deconfinement phase transition are obtained with potential detectability in the International Pulsar Timing Array and Square Kilometre Array in the near future when the associated productions of primordial black holes (PBHs) saturate the current observational bounds on the PBH abundances from the LIGO-Virgo-Collaboration O3 data.

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S. He, L. Li, Z. Li, et. al.
Wed, 26 Oct 22
33/73

Comments: 5 pages + appendix, 5 figures

Clusteringenesis: from Light to Heavy Primordial Black Holes [CEA]

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http://arxiv.org/abs/2210.14171


We show that heavy primordial black holes may originate from much lighter ones if the latter are strongly clustered at the time of their formation. While this population is subject to the usual constraints from late-time universe observations, its relation to the initial conditions is different from the standard scenario and provides a new mechanism to generate massive primordial black holes even in the absence of efficient accretion, opening new scenarios, e.g. for the generation of supermassive black holes.

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V. Luca, G. Franciolini and A. Riotto
Wed, 26 Oct 22
45/73

Comments: 5 pages, 2 figures

Inflation from Multiple Pseudo-Scalar Fields: PBH Dark Matter and Gravitational Waves [CEA]

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http://arxiv.org/abs/2210.13822


We study a model of inflation with multiple pseudo-scalar fields coupled to a $U(1)$ gauge field through Chern-Simons interactions. Because of parity violating interactions, one polarization of the gauge field is amplified yielding to enhanced curvature perturbation power spectrum. Inflation proceeds in multiple stages as each pseudo-scalar field rolls towards its minimum yielding to distinct multiple peaks in the curvature perturbations power spectrum at various scales during inflation. The localized peaks in power spectrum generate Primordial Black Holes (PBHs) which can furnish a large fraction of Dark Matter (DM) abundance. In addition, gravitational waves (GWs) with non-trivial spectra are generated which are in sensitivity range of various forthcoming GW observatories.

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A. Talebian, S. Mansoori and H. Firouzjahi
Wed, 26 Oct 22
47/73

Comments: This work is dedicated to the memory of Prof. Mohammad Reza Setare (1974-2022)

Cosmological consequences of first-order general-relativistic viscous fluid dynamics [CL]

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http://arxiv.org/abs/2210.13372


We investigate the out-of-equilibrium dynamics of viscous fluids in a spatially flat Friedmann-Lema\^itre-Robertson-Walker cosmology using the most general causal and stable viscous energy-momentum tensor defined at first order in spacetime derivatives. In this new framework a pressureless viscous fluid having density $\rho$ can evolve to an asymptotic future solution in which the Hubble parameter approaches a constant while $\rho \rightarrow 0$, even in the absence of a cosmological constant (i.e., $\Lambda = 0$). Thus, while viscous effects in this model drive an accelerated expansion of the universe, the density of the viscous component itself vanishes, leaving behind only the acceleration. This behavior emerges as a consequence of causality in first-order theories of relativistic fluid dynamics and it is fully consistent with Einstein’s equations.

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F. Bemfica, M. Disconzi, J. Noronha, et. al.
Tue, 25 Oct 22
85/111

Comments: 14 pages, no figures

Echo of the Dark: Gravitational Waves from Dark SU(3) Yang-Mills Theory [CL]

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http://arxiv.org/abs/2210.11821


We analyze the phase transition in improved holographic QCD to obtain an estimate of the gravitational wave signal emitted in the confinement transition of a pure SU(3) Yang-Mills dark sector. We derive the effective action from holography and show that the energy budget and duration of the phase transition can be calculated with minor errors. These are used as input to obtain a prediction of the gravitational wave signal. To our knowledge, this is the first computation of the gravitational wave signal in a holographic model designated to match lattice data on the thermal properties of pure Yang-Mills.

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E. Morgante, N. Ramberg and P. Schwaller
Mon, 24 Oct 22
43/56

Comments: N/A

The Search for the Topology of the Universe Has Just Begun [CEA]

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http://arxiv.org/abs/2210.11426


Anomalous large-angle cosmic microwave background anisotropies motivate further searches for cosmic topology. We demonstrate that for generic topologies of spatially flat spacetimes, off-diagonal correlations between microwave background harmonic coefficients over a wide range of scales encode significant topological information, even if the topology scale substantially exceeds the diameter of the observable Universe. Observational searches have so far considered only a small subset of testable topologies, and current limits on the topology scale are much weaker than generally understood.

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Y. Akrami, C. Copi, J. Eskilt, et. al.
Fri, 21 Oct 22
23/76

Comments: 7 pages, 3 figures

SMEFT effects on gravitational wave spectrum from electroweak phase transition [CL]

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http://arxiv.org/abs/2210.11241


Future gravitational wave observations are potentially sensitive to new physics corrections to the Higgs potential once the first-order electroweak phase transition arises. We study the SMEFT dimension-six operator effects on the Higgs potential, where three types of effects are taken into account: (i) SMEFT tree level effect on $\varphi^6$ operator, (ii) SMEFT tree level effect on the wave function renormalization of the Higgs field, and (iii) SMEFT top-quark one-loop level effect. The sensitivity of future gravitational wave observations to these effects is numerically calculated by performing a Fisher matrix analysis. We find that the future gravitational wave observations can be sensitive to (ii) and (iii) once the first-order electroweak phase transition arises from (i). The sensitivities of the future gravitational wave observations are also compared with those of future collider experiments.

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K. Hashino and D. Ueda
Fri, 21 Oct 22
32/76

Comments: 25 pages, 13 figures

Multifield Positivity Bounds for Inflation [CL]

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http://arxiv.org/abs/2210.10791


Positivity bounds represent nontrivial limitations on effective field theories (EFTs) if those EFTs are to be completed into a Lorentz-invariant, causal, local, and unitary framework. While such positivity bounds have been applied in a wide array of physical contexts to obtain useful constraints, their application to inflationary EFTs is subtle since Lorentz invariance is spontaneously broken during cosmic inflation. One path forward is to employ a $\textit{Breit parameterization}$ to ensure a crossing-symmetric and analytic S-matrix in theories with broken boosts. We extend this approach to a theory with multiple fields, and uncover a fundamental obstruction that arises unless all fields obey a dispersion relation that is approximately lightlike. We then apply the formalism to various classes of inflationary EFTs, with and without isocurvature perturbations, and employ this parameterization to derive new positivity bounds on such EFTs. For multifield inflation, we also consider bounds originating from the generalized optical theorem and demonstrate how these can give rise to stronger constraints on EFTs compared to constraints from traditional elastic positivity bounds alone. We compute various shapes of non-Gaussianity (NG), involving both adiabatic and isocurvature perturbations, and show how the observational parameter space controlling the strength of NG can be constrained by our bounds.

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M. Freytsis, S. Kumar, G. Remmen, et. al.
Fri, 21 Oct 22
56/76

Comments: 49 pages, 4 figures

Generalized $R^p$-attractor Cosmology in the Jordan and Einstein Frames: New Type of Attractors and Revisiting Standard Jordan Frame $R^p$ Inflation [CL]

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http://arxiv.org/abs/2210.11351


In this work we shall study a new class of attractor models which we shall call generalized $R^p$-attractor models. This class of models is based on a generalization of the Einstein frame potential of $R^p$ $f(R)$ gravity models in the Jordan frame. We present the attractor properties of the corresponding non-minimally coupled Jordan frame theory, and we calculate the observational indices of inflation in the Einstein frame. As we show, there is a large class of non-minimally coupled scalar theories, with an arbitrary non-minimal coupling which satisfies certain conditions, that yield the same Einstein frame potential, this is why these models are characterized attractors. As we demonstrate, the generalized $R^p$-attractor models are viable and well fitted within the Planck constraints. This includes the subclass of the generalized $R^p$-attractor models, namely the Einstein frame potential of $R^p$ inflation in the Jordan frame, a feature also known in the literature. We also highlight an important issue related to the $R^p$ inflation in the Jordan frame, which is known to be non-viable. By conformal invariance, the $R^p$ inflation model should also be viable in the Jordan frame, which is not. We pinpoint the source of the problem using two different approaches in the $f(R)$ gravity Jordan frame, and as we demonstrate, the problem arises in the literature due to some standard simplifications made for the sake of analyticity. We demonstrate the correct way to analyze $R^p$ inflation in the Jordan frame, using solely the slow-roll conditions.

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S. Odintsov and V. Oikonomou
Fri, 21 Oct 22
75/76

Comments: IJMPD Accepted

Why is zero spatial curvature special? [CEA]

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http://arxiv.org/abs/2210.10102


Evidence for almost spatial flatness of the Universe has been provided from several observational probes, including the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO) from galaxy clustering data. However, other than inflation, and in this case only in the limit of infinite time, there is no strong a priori motivation for a spatially flat Universe. Using the renormalization group (RG) technique in curved spacetime, we present in this work a theoretical motivation for spatial flatness. Starting from a general spacetime, the first step of the RG, coarse-graining, gives a Friedmann-Lema\^itre-Robertson-Walker (FLRW) metric with a set of parameters. Then, we study the rescaling properties of the curvature parameter, and find that zero spatial curvature of the FLRW metric is singled out as the unique scale-free, non-singular background for cosmological perturbations.

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R. Jimenez, A. Khalife, D. Litim, et. al.
Thu, 20 Oct 22
5/74

Comments: N/A

Distinguishing a Slowly Accelerating Black Hole by Differential Time Delays of Images [CL]

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http://arxiv.org/abs/2210.10762


Accelerating supermassive black holes, connected to cosmic strings, could contribute to structure formation and get captured by galaxies if their velocities are small. This would mean that the acceleration of these black holes is small too. Such a slow acceleration has no significant effect on the shadow of such supermassive black holes. We also show that, for slowly accelerating black holes, the angular position of images in the gravitational lensing effects do not change significantly. We propose a method to observe the acceleration of these black holes through the gravitational lensing. The method is based on the observation that differential time delays associated with the images are substantially different with respect to the case of non-accelerating black holes.

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A. Ashoorioon, M. Poshteh and R. Mann
Thu, 20 Oct 22
6/74

Comments: 5 pages, 3 figures, matched the published version in PRL. arXiv admin note: substantial text overlap with arXiv:2110.13132

Reconstructing inflation and reheating in $f(φ)T$ gravity [CL]

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http://arxiv.org/abs/2210.10080


The reconstruction of an inflationary universe in the context of one $f(\phi)T$ gravity, in which $T$ corresponds to the trace of energy momentum tensor is studied. To realize this reconstruction during the inflationary epoch, we consider as attractor the scalar spectral index $n_s$ in terms of of the number of $e$-folds $N$, in the framework of the slow-roll approximation. By assuming a specific function $f(\phi)$ together with the simplest attractor $n_s(N)$, we find different expressions for the reconstructed effective potential $V(\phi)$. Additionally, we analyze the era of reheating occurs after of the reconstruction obtained during the inflationary epoch. In this scenario we determine the duration and temperature during the reheating epoch, in terms of the equation of state parameter and the observational parameters. In this context, the different parameters associated to the reconstructed model are restricted during the scenarios of inflation and reheating by considering the recent astronomical observations.

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R. Herrera and C. Rios
Thu, 20 Oct 22
26/74

Comments: 16 pages and 6 figures

Pole inflation and primordial black holes formation in Starobinsky-like supergravity [CL]

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http://arxiv.org/abs/2210.10348


We extend the Cecotti-Kallosh model of Starobinsky inflation in supergravity by adding a holomorphic function to the superpotential in order to generate a large peak in the power spectrum of scalar (curvature) perturbations. In our approach, the singular non-canonical kinetic terms are largely responsible for inflation (as an attractor solution), whereas the superpotential is engineered to generate a production of primordial black holes. We study the cases with (i) a linear holomorphic function, (ii) a quadratic holomorphic function, and (iii) an exponential holomorphic function, as regards the dependence of inflation and primordial black holes production upon parameters of those functions and initial conditions, as well as verify viability of inflation with our superpotentials. We find that an efficient production of primordial black holes consistent with CMB measurements is only possible in the second (ii) case. We calculate the masses of the produced primordial black holes and find that they are below the Hawking (black hole) evaporation limit, so that they cannot be part of the current dark matter in our Universe.

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S. Aoki, R. Ishikawa and S. Ketov
Thu, 20 Oct 22
34/74

Comments: 22 pages, 16 figures, LaTeX

Inflation and Electroweak Symmetry Breaking [CL]

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http://arxiv.org/abs/2210.10735


We present a model of Cosmological Electroweak Symmetry Breaking (CEWSB), where a Higgs-like field and a cosmological background of weak boson gauge fields interact with gravity to realize the epoch of cosmic inflation, which is then followed by a Higgs resonance preheating. As a result, the scale of electroweak symmetry breaking is linked with the end of inflation. The theory is equipped with a shift symmetry that can protect the Higgs mass, and it has close semblance to natural inflation and its variants. As the Higgs field’s amplitude decays at the end of inflation, its mass emerges. The model has a built in Higgs self-resonance preheating mechanism which leads to the possible emergence of the cosmic microwave background (CMB) due to resonant Higgs, quark and lepton production after inflation. We provide a pathway to implement a similar mechanism with the realistic Higgs-doublet of the standard electroweak theory and discuss phenomenological considerations.

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S. Alexander
Thu, 20 Oct 22
36/74

Comments: 7 pages

Extensions of two-field mimetic gravity [CL]

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http://arxiv.org/abs/2210.10499


Two-field mimetic gravity was recently realized by looking at the singular limit of the conformal transformation between the auxiliary metric and the physical metric with two scalar fields involved. In this paper, we reanalyze the singular conformal limit and find a more general solution for the conformal factor A, which greatly broadens the form of two-field mimetic constraint and thus extends the two-field mimetic gravity. We find the general setup still mimics the roles of dark matter at the cosmological background level. Moreover, we extend the action by introducing extra possible term for phenomenological interests. Surprisingly, some special cases are found to be equivalent to general relativity, k-essence theory and Galileon theory. Finally, we further extend the theory by allowing the expression of mimetic constraint to be arbitrary without imposed condition, and show that the dark matter-like behavior is unaffected even in this extension.

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Y. Zheng and H. Rao
Thu, 20 Oct 22
64/74

Comments: 17 pages, comments are welcome

Does the gamma-ray binary LS I +61 303 harbour a magnetar? [HEAP]

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http://arxiv.org/abs/2210.09471


LS I +61{\deg}303 is a high mass X-ray binary that is also catalogued as a gamma-ray binary as a result of frequent outbursts at TeV photon energies. The system has released two soft-gamma flares in the past, suggesting a magnetar interpretation for the compact primary. This inference has recently gained significant traction following the discovery of transient radio pulses, detected in some orbital phases from the system, as the measured rotation and tentative spindown rates imply a polar magnetic field strength of $B_p \gtrsim 10^{14}\,\mbox{G}$ if the star is decelerating via magnetic dipole braking. In this paper, we scrutinise magnetic field estimates for the primary in LS I +61{\deg}303 by analysing the compatibility of available data with the system’s accretion dynamics, spin evolution, age limits, gamma-ray emissions, and radio pulsar activation. We find that the neutron star’s age and spin evolution are theoretically difficult to reconcile unless a strong propeller torque is in operation. This torque could be responsible for the bulk of even the maximum allowed spindown, potentially weakening the inferred magnetic field by more than an order of magnitude.

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A. Suvorov and K. Glampedakis
Wed, 19 Oct 22
17/87

Comments: 12 pages, 5 figures. Accepted for publication in ApJ

New Constraints on Dark Matter and Cosmic Neutrino Profiles through Gravity [CL]

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http://arxiv.org/abs/2210.03749


We derive purely gravitational constraints on dark matter and cosmic neutrino profiles in the solar system using asteroid (101955) Bennu. We focus on Bennu because of its extensive tracking data and high-fidelity trajectory modeling resulting from the OSIRIS-REx mission. We find that the local density of dark matter is bound by $\rho_{\rm DM}\lesssim 3.3\times 10^{-15}\;\rm kg/m^3 \simeq 6\times10^6\,\bar{\rho}{\rm DM}$, in the vicinity of $\sim 1.1$ au (where $\bar{\rho}{\rm DM}\simeq 0.3\;\rm GeV/cm^3$). We show that high-precision tracking data of solar system objects can constrain cosmic neutrino overdensities relative to the Standard Model prediction $\bar{n}{\nu}$, at the level of $\eta\equiv n\nu/\bar{n}{\nu}\lesssim 1.7 \times 10^{11}(0.1 \;{\rm eV}/m\nu)$ (Saturn), comparable to the existing bounds from KATRIN and other previous laboratory experiments (with $m_\nu$ the neutrino mass). These local bounds have interesting implications for existing and future direct-detection experiments. Our constraints apply to all dark matter candidates but are particularly meaningful for scenarios including solar halos, stellar basins, and axion miniclusters, which predict or allow overdensities in the solar system. Furthermore, introducing a DM-SM long-range fifth force with a strength $\tilde{\alpha}D$ times stronger than gravity, Bennu can set a constraint on $\rho{\rm DM}\lesssim \bar{\rho}_{\rm DM}\left(6 \times 10^6/\tilde{\alpha}_D\right)$. These constraints can be improved in the future as the accuracy of tracking data improves, observational arcs increase, and more missions visit asteroids.

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Y. Tsai, J. Eby, J. Arakawa, et. al.
Wed, 19 Oct 22
33/87

Comments: 2 figures, 2 tables, 9 pages plus references

Upper limits on the Polarized Isotropic Stochastic Gravitational-Wave Background from Advanced LIGO-Virgo's First Three Observing Runs [CEA]

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http://arxiv.org/abs/2210.09952


Parity violation is expected to generate an asymmetry between the amplitude of left and right-handed gravitational-wave modes which leads to a circularly polarized stochastic gravitational-wave background (SGWB). Due to the three independent baselines in the LIGO-Virgo network, we focus on the amplitude difference in strain power characterized by Stokes’ parameters and do maximum-likelihood estimation to constrain the polarization degree of SGWB. Our results indicate that there is no evidence for the circularly polarized SGWB in the data. Furthermore, by modeling the SGWB as a power-law spectrum, we place upper limit on the normalized energy density $\Omega_\text{gw}(25\,\text{Hz})<5.3\times10^{-9}$ at $95\%$ confidence level after marginalizing over the polarization degree and spectral index.

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Y. Jiang and Q. Huang
Wed, 19 Oct 22
42/87

Comments: 6 pages, 4 figures and 2 tables

Constraints on Late Time Violations of the Equivalence Principle in the Dark Sector [CL]

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http://arxiv.org/abs/2210.09732


If dark energy is dynamical due to the evolution of a scalar field, then in general it is expected that the scalar is coupled to matter. While couplings to the standard model particles are highly constrained by local experiments, bounds on couplings to dark matter (DM) are only obtained from cosmological observations and they are consequently weaker. It has recently be pointed out that the coupling itself can become non-zero only at the time of dark energy domination, due to the evolution of dark energy itself, leading to a violation of the equivalence principle (EP) in the dark sector at late times. In this paper we study a specific model and show that such late-time violations of the EP in the DM sector are not strongly constrained by the evolution of the cosmological background and by observables in the linear regime (e.g. from the cosmic microwave background radiation). A study of perturbations in non-linear regime is necessary to constrain late–time violations of the equivalence principle much more strongly.

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C. Thomas and C. Bruck
Wed, 19 Oct 22
81/87

Comments: 9 pages, 3 figures, 2 tables

Heating up Peccei-Quinn scale [CL]

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http://arxiv.org/abs/2210.08407


We discuss production of QCD axions in a novel scenario, which assumes time-varying scale of Peccei-Quinn symmetry breaking. The latter decreases as the Universe’s temperature at early times and eventually stabilises at a large constant value. Such behavior is caused by the portal interaction between the complex field carrying Peccei-Quinn charge and a Higgs-like scalar, which is in thermal equilibrium with primordial plasma. In this scenario, axions are efficiently produced during the parametric resonance decay of the complex Peccei-Quinn field, relaxing to the minimum of its potential in the radiation-dominated stage. Notably, this process is not affected by the Universe’s expansion rate and allows to generate the required abundance of dark matter independently of an axion mass. This remains the case in the narrow parametric resonance regime corresponding to small oscillation amplitudes. Phenomenological constraints on the model parameter space strongly depend on the number density of radial field fluctuations, which are also generically excited along with axions. Even if produced with a small abundance relative to axions, radial fluctuations can have a sizeable impact on the BBN and the CMB through their decay products contributing to dark radiation. Existing constraints on dark radiation bound Peccei-Quinn symmetry breaking scale below $10^{8}-10^{9}~\mbox{GeV}$ – this paves the way for ruling out our scenario with the near future searches for axions.

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S. Ramazanov and R. Samanta
Tue, 18 Oct 22
4/99

Comments: 25 pages, 3 figures

On thermal false vacuum decay around black holes [CL]

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http://arxiv.org/abs/2210.08028


In flat space and at finite temperature, there are two regimes of false vacuum decay in quantum field theory. At low temperature, the decay proceeds through thermally-assisted tunneling described by periodic Euclidean solutions — bounces — with non-trivial time dependence. On the other hand, at high temperature the bounces are time-independent and describe thermal jumps of the field over the potential barrier. We argue that only solutions of the second type are relevant for false vacuum decay catalyzed by a black hole in equilibrium with thermal bath. The argument applies to a wide class of spherical black holes, including $d$-dimensional AdS/dS-Schwarzschild black holes and Reissner-Nordstr\”om black holes sufficiently far from criticality. It does not rely on the thin-wall approximation and applies to multi-field scalar theories.

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V. Briaud, A. Shkerin and S. Sibiryakov
Tue, 18 Oct 22
57/99

Comments: 7 pages, 2 figures

Black hole merger simulations in wave dark matter environments [CL]

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http://arxiv.org/abs/2210.09254


The interaction of binary black hole mergers with their environments can be studied using numerical relativity simulations. These start only a short finite time before merger, at which point appropriate initial conditions must be imposed. A key task is therefore to identify the configuration that is appropriate for the binary and its environment at this stage of the evolution. In this work we study the behaviour of wave dark matter around equal mass black hole binaries, finding that there is a preferred, quasi-stationary profile that persists and grows over multiple orbits, in contrast to heavier mass dark matter where any overdensity tends to be dispersed by the binary motion. Whilst different initial configurations converge to the preferred quasi-stationary one after several orbits, unwanted transient oscillations are generated in the process, which may impact on the signal in short simulation runs. We also point out that naively superimposing the matter onto a circular binary results in artificially eccentric orbits due to the matter backreaction, which is an effect of the initial conditions and not a signature of dark matter. We discuss the further work required so that comparison of waveforms obtained with environments to vacuum cases can be done in a meaningful way.

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J. Bamber, J. Aurrekoetxea, K. Clough, et. al.
Tue, 18 Oct 22
96/99

Comments: 9 pages, 5 figures, 1 appendix, 2 movies: this https URL Comments welcome!

BFSS Matrix Model Cosmology: Progress and Challenges [CL]

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http://arxiv.org/abs/2210.07288


We review a proposal to obtain an emergent metric space-time and an emergent early universe cosmology from the BFSS matrix model. Some challenges and directions for future research are outlined.

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S. Brahma, R. Brandenberger and S. Laliberte
Mon, 17 Oct 22
12/56

Comments: 7 pages, 1 figure

Conformal model for gravitational waves and dark matter: A status update [CEA]

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http://arxiv.org/abs/2210.07075


We present an updated analysis of the first-order phase transition associated with symmetry breaking in the early Universe in a classically scale-invariant model extended with a new SU(2) gauge group. Including recent developments in understanding supercooled phase transitions, we compute all of its characteristics and significantly constrain the parameter space. We then predict gravitational wave spectra generated during this phase transition and by computing the signal-to-noise ratio we conclude that this model is well testable (and falsifiable) with LISA. We also provide predictions for the relic dark matter abundance. It is consistent with observations in a rather narrow part of the parameter space, since we exclude the so-called supercool dark matter scenario based on an improved description of percolation and reheating after the phase transition as well as inclusion of the running of couplings. Finally, we devote attention to renormalisation-scale dependence of the results. Even though our main results are obtained with the use of renormalisation-group improved effective potential, we also perform a fixed-scale analysis which proves that the dependence on the scale is not only qualitative but also quantitative.

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M. Kierkla, A. Karam and B. Swiezewska
Fri, 14 Oct 22
21/75

Comments: N/A

Lifetime of scalar cloud formation around a rotating regular black hole [CL]

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http://arxiv.org/abs/2210.06861


Does circumventing the curvature singularity of the Kerr black hole affects the timescale of the scalar cloud formation around it? By definition, the scalar cloud, forms a gravitational atom with hydrogen-like bound states, lying on the threshold of a massive scalar field’s superradiant instability regime (time-growing quasi-bound states) and beyond (time-decaying quasi-bound states). By taking a novel type of rotating hollow regular black hole proposed by Simpson and Visser which unlike its standard rivals has an asymptotically Minkowski core, we address this question. The metric has a minimal extension relative to the standard Kerr, originating from a single regularization parameter $\ell$, with length dimension. We show with the inclusion of the regularization length scale $\ell$ into the Kerr spacetime, without affecting the standard superradiant instability regime, the timescale of scalar cloud formation gets shorter. Since the scalar cloud after its formation, via energy dissipation, can play the role of a continuum source for gravitational waves, such a reduction in the instability growth time improves the phenomenological detection prospects of new physics because the shorter the time, the more astrophysically important.

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M. Khodadi and R. Pourkhodabakhshi
Fri, 14 Oct 22
48/75

Comments: 13 pages (two column), 6 figures, 1 table

Minisuperspace Quantum Cosmology from the Einstein-Cartan Path Integral [CL]

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http://arxiv.org/abs/2210.05583


We derive the fixed-$\Lambda$ and unimodular propagators using the path integral formalism as applied to the Einstein-Cartan action. The simplicity of the action (which is linear in the lapse function) allows for an exact integration starting from the lapse function and the enforcement of the Hamiltonian constraint, leading to a product of Chern-Simons states if the connection is fixed at the endpoints. No saddle point approximation is needed. Should the metric be fixed at the endpoints, then, depending on the contour chosen for the connection, Hartle-Hawking or Vilenkin propagators are obtained. Thus, in this approach one trades a choice of contour in the lapse function for one in the connection, where appropriate. The unimodular propagators are also trivial to obtain via the path integral, and the previously derived expressions are recovered.

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R. Isichei and J. Magueijo
Fri, 14 Oct 22
51/75

Comments: N/A

Modified gravity approaches to the cosmological constant problem [CL]

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http://arxiv.org/abs/2210.06810


The cosmological constant and its phenomenology remain among the greatest puzzles in theoretical physics. We review how modifications of Einstein’s general relativity could alleviate the different problems associated with it that result from the interplay of classical gravity and quantum field theory. We introduce a modern and concise language to describe the problems associated with its phenomenology, and inspect no-go theorems and their loopholes to motivate the approaches discussed here. Constrained gravity approaches exploit minimal departures from general relativity; massive gravity introduces mass to the graviton; Horndeski theories lead to the breaking of translational invariance of the vacuum; and models with extra dimensions change the symmetries of the vacuum. We also review screening mechanisms that have to be present in some of these theories if they aim to recover the success of general relativity on small scales as well. Finally, we summarise the statuses of these models in their attempt to solve the different cosmological constant problems while being able to account for current astrophysical and cosmological observations.

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F. Collaboration, H. Bernardo, B. Bose, et. al.
Fri, 14 Oct 22
55/75

Comments: 54 pages, 2 figures, 1 table. Invited review for Universe, Special Issue “Cosmological Constant” (this https URL)

Effective dark energy through spin-gravity coupling [CL]

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http://arxiv.org/abs/2210.06598


We investigate cosmological scenarios with spin-gravity coupling. In particular, due to the spin of the baryonic and dark matter particles and its coupling to gravity, they probe an effective spin-dependent metric, which can be calculated semi-classically in the Mathisson-Papapetrou-Tulczyjew-Dixon formalism. Hence, the usual field equations give rise to modified Friedmann equations, in which the extra terms can be identified as an effective dark-energy sector. Additionally, we obtain an effective interaction between the matter and dark-energy sectors. In the case where the spin-gravity coupling switches off, we recover standard $\Lambda$CDM cosmology. We perform a dynamical system analysis and we find a matter-dominated point that can describe the matter era, and a stable late-time solution corresponding to acceleration and dark-energy domination. For small values of the spin coupling parameter, deviations from $\Lambda$CDM concordance scenario are small, however for larger values they can be brought to the desired amount, leading to different dark-energy equation-of-state parameter behavior, as well as to different transition redshift from acceleration to deceleration. Finally, we confront the model predictions with Hubble function data.

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G. Otalora and E. Saridakis
Fri, 14 Oct 22
63/75

Comments: 7 pages, 4 figures

Fifth forces and frame invariance [CL]

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http://arxiv.org/abs/2210.06396


I discuss how one can apply the covariant formalism developed by Vilkovisky and DeWitt to obtain frame invariant fifth force calculations for scalar-tensor theories. Fifth forces are severely constrained by astrophysical measurements. It was shown previously that for scale-invariant Higgs-dilaton gravity, in a particular choice of Jordan frame, the dilaton fifth force is dramatically suppressed, evading the observational constraints. Using a geometric approach I extend this result to all frames, and show that the usual dichotomy of “Jordan frame” versus “Einstein frame” is better understood as a continuum of frames: submanifold slices of a more general field space.

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J. Bamber
Thu, 13 Oct 22
18/68

Comments: 12 pages, 1 figure

Return of Harrison-Zeldovich spectrum in light of recent cosmological tensions [CEA]

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http://arxiv.org/abs/2210.06125


The spectral index $n_s$ of scalar perturbation is the significant initial condition set by inflation theory for our observable Universe. According to Planck results, current constraint is $n_s = 0.965\pm 0.004$, while an exact scale-invaiant Harrison-Zeldovich spectrum, i.e. $n_s=1$, has been ruled out at $8.4\sigma$ significance level. However, it is well-known that the standard $\Lambda$CDM model is suffering from the Hubble tension, which is at $\sim 5\sigma$ significance level. This inconsistency likely indicates that the comoving sound horizon at last scattering surface is actually lower than expected, which so seems to be calling for the return of $n_s=1$. Here, in light of recent observations we find strong evidence for a $n_s=1$ Universe. And we show that if so, it would be confirmed conclusively by CMB-S4 experiment.

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J. Jiang, G. Ye and Y. Piao
Thu, 13 Oct 22
22/68

Comments: 21 pages, 5 figures

Electroweak Asymmetric Early Universe via a Scalar Condensate [CL]

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http://arxiv.org/abs/2210.05680


Finite temperature effects in the Standard Model tend to restore the electroweak symmetry in the early universe, but new fields coupled to the higgs field may as well reverse this tendency, leading to the so-called electroweak symmetry non-restoration (EW SNR) scenario. Previous works on EW SNR often assume that the reversal is due to the thermal fluctuations of new fields with negative quartic couplings to the higgs, and they tend to find that a large number of new fields are required. We observe that EW SNR can be minimally realized if the field(s) coupled to the higgs field develop(s) a stable condensate. We show that one complex scalar field with a sufficiently large global-charge asymmetry can develop a condensate as an outcome of thermalization and keep the electroweak symmetry broken up to temperatures well above the electroweak scale. In addition to providing a minimal benchmark model, our work hints on a class of models involving scalar condensates that yield electroweak symmetry non-restoration in the early universe.

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J. Chang, M. Olea-Romacho and E. Tanin
Thu, 13 Oct 22
35/68

Comments: N/A