Gravitino and Polonyi production in supergravity [CL]

We study production of gravitino and Polonyi particles in the minimal Starobinsky-Polonyi $\mathcal{N}=1$ supergravity with inflaton belonging to a massive vector supermultiplet. Our model has only one free parameter given by the scale of spontaneous SUSY breaking triggered by Polonyi chiral superfield. The vector supermultiplet generically enters the action non-minimally, via an arbitrary real function. This functon is chosen to generate the inflaton scalar potential of the Starobinsky model. Our supergravity model can be reformulated as an abelian supersymmetric gauge theory with the vector gauge superfield coupled to two (Higgs and Polonyi) chiral superfields interacting with supergravity, where the $U(1)$ gauge symmetry is spontaneously broken. We find that Polonyi and gravitino particles are efficiently produced during inflation. After inflation, perturbative decay of inflaton also produces Polonyi particles that rapidly decay into gravitinos. As a result, a coherent picture of inflation and dark matter emerges, where the abundance of produced gravitinos after inflation fits the CMB constraints as a Super Heavy Dark Matter (SHDM) candidate. Our scenario avoids the notorous gravitino and Polonyi problems with the Big Bang Nucleosynthesis (BBN) and DM overproduction.

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A. Addazi, S. Ketov and M. Khlopov
Mon, 21 Aug 17

Comments: N/A

Cosmological Tests of Everpresent $Λ$ [CL]

Everpresent $\Lambda$ is a cosmological scenario in which the observed cosmological “constant” $\Lambda$ fluctuates between positive and negative values with a vanishing mean, and with a magnitude comparable to the critical density at any epoch. In accord with a longstanding heuristic prediction of causal set theory, it postulates that $\Lambda$ is a stochastic function of cosmic time that will vary from one realization of the scenario to another. Herein, we consider two models of “dark energy” that exhibit these features. Via Monte Carlo Markov chains, we explore the space of cosmological parameters and the set of stochastic realizations of these models, finding that Everpresent $\Lambda$ can fit the current cosmological observations as well as the $\Lambda$CDM model does. Furthermore, it removes observational tensions with $\Lambda$CDM, for low redshift measurements of Hubble constant, and the Baryonic Acoustic Oscillations (BAO) in Lyman-$\alpha$ forest at $z\sim 2-3$. However, we also find that Everpresent $\Lambda$ does not significantly help with the growth of ultramassive black holes at high redshift, and the Lithium problem in Big Bang Nuclesynthesis. Future measurements of “dark energy” at high redshifts will further test the viability of Everpresent $\Lambda$ as an alternative to the $\Lambda$CDM cosmology.

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N. Zwane, N. Afshordi and R. Sorkin
Mon, 21 Aug 17

Comments: N/A

Beyond delta: Tailoring marked statistics to reveal modified gravity [CEA]

Models that seek to explain cosmic acceleration through modifications to General Relativity (GR) evade stringent Solar System constraints through a restoring, screening mechanism. Down-weighting the high density, screened regions in favor of the low density, unscreened ones offers the potential to enhance the amount of information carried in such modified gravity models.
In this work, we assess the performance of a new “marked” transformation and perform a systematic comparison with the clipping and logarithmic transformations, in the context of $\Lambda$CDM and the symmetron and $f(R)$ modified gravity models. Performance is measured in terms of the boost in the signal-to-noise ratio (SNR) for these models relative to the statistics derived from the standard density distribution. We find that all three statistics provide improved SNR boosts over the basic density statistics. The model parameters for the “marked” and clipped transformation that best enhance signals and the SNR boosts are determined. When including scales $k>3 h/Mpc$ we find that the clipped transformation produces the highest SNR boost, while for a more conservative scenario, considering scales down to $\sim$1-2$h/Mpc$, we find that the marked transformation performs best. We also show that the mark is useful both as a Fourier and real space transformation; a marked correlation function also enhances the SNR relative to the standard correlation function, and can on mildly non-linear scales show a significant difference between the $\Lambda$CDM and the modified gravity models.
Our results demonstrate how a series of simple analytical transformations could dramatically increase the predicted information extracted on deviations from GR, from large-scale surveys, and give the prospect for a potential detection much more feasible.

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G. Valogiannis and R. Bean
Mon, 21 Aug 17

Comments: 9 pages, 6 figures

Singularities and Cyclic Universes [CL]

The models of cyclic universes and cyclic multiverses based on the alternative gravity theories of varying constants are considered.

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M. Dabrowski
Fri, 18 Aug 17

Comments: 4 pages, no figures

On Thermal Gravitational Contribution to Particle Production and Dark Matter [CL]

We investigate the particle production from thermal gravitational annihilation in the very early universe, which is an important contribution for particles that might not be in thermal equilibrium or/and only have gravitational interaction, such as dark matter (DM). For particles with spin 0, 1/2 and 1 we calculate the relevant cross sections through gravitational annihilation and give the analytic formulas with full mass-dependent terms. We find that DM with mass between TeV and $10^{16}$GeV could have the relic abundance that fits the observation, with small dependence on its spin. We also discuss the effects of gravitational annihilation from inflatons. Interestingly, contributions from inflatons could be dominant and have the same power dependence on Hubble parameter of inflation as that from vacuum fluctuation. Also, fermion production from inflatons, in comparison to boson, is suppressed by its mass due to helicity selection.

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Y. Tang and Y. Wu
Fri, 18 Aug 17

Comments: 10 pages, 3 figures and 2 tables

Regular Multi-Horizon Black Holes in Modified Gravity with Non-Linear Electrodynamics [CL]

We investigated the regular multi-horizon black holes in the Einstein gravity, $F(R)$ gravity and the 5 dimensional Gauss-Bonnet gravity, all of them coupled with non-linear electrodynamics. We presented several explicit examples of the actions which admit the solutions describing regular black hole space-time with multi-horizons. Thermodynamics of the obtained black hole solutions is studied. The explicit expressions of the temperature, the entropy, the thermodynamical energy and the free energy are obtained. Although the temperature vanishes in the extremal limit where the radii of the two horizons coincide with each other as in the standard multi-horizon black hole like the Reissner-Nordstr\” om black hole or the Kerr black hole, the larger temperature corresponds to the larger horizon radius. This is different from the standard black holes, where the larger temperature corresponds to the smaller horizon radius. We also found that the specific heat becomes positive for the large temperature, which is also different from the standard black holes, where the specific heat is negative. It should be also noted that the thermodynamical energy is not identical with the ADM mass. Furthermore in case of the Gauss-Bonnet gravity,it is demonstrated that the entropy can become negative.

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S. Nojiri and S. Odintsov
Fri, 18 Aug 17

Comments: LaTeX 17 pages

Cosmological Zero Modes [CEA]

We introduce a new family of primordial cosmological perturbations that are not described by traditional power spectra. At the linear level, these perturbations live in the kernel of the spatial Laplacian operator, and thus we call them cosmological zero modes. We compute the cosmic microwave background (CMB) temperature and polarization anisotropy induced by these modes, and forecast their detection sensitivity using a cosmic-variance limited experiment. In particular, we consider two configurations for the zero modes: The first configuration consists of stochastic metric perturbations described by white noise on a “holographic screen” located at our cosmological horizon. The amplitude of the power spectrum of this white noise can be constrained to be $\lesssim 9 \times 10^{-14}$. The second configuration is a primordial monopole beyond our cosmological horizon. We show that such a monopole, with “charge” $Q$, can be detected in the CMB sky up to a distance of $11.6 ~ Q^{1/4}\times$ horizon radius (or $160~ Q^{1/4}$ Gpc). More generally, observational probes of cosmological zero modes can shed light on non-perturbative phenomena in the primordial universe, beyond our observable horizon.

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N. Afshordi and M. Johnson
Thu, 17 Aug 17

Comments: 11 pages, 4 figures. Comments are welcome