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Pavel Fileviez Perez, Elliot Golias, Rui-Hao Li, Clara Murgui

We discuss the possible connection between the scale for baryon number violation and the cosmological bound on the dark matter relic density.

A simple gauge theory for baryon number which predicts the existence of a leptophobic cold dark matter particle candidate is investigated. 

In this context, the dark matter candidate is a Dirac fermion with mass defined by the new symmetry breaking scale. Using the 

cosmological bounds on the dark matter relic density we find the upper bound on the symmetry breaking scale around 200 TeV. 

The properties of the leptophobic dark matter candidate are investigated in great detail and we show the prospects to test 

this theory at current and future experiments. We discuss the main implications for the mechanisms to explain the matter

and antimatter asymmetry in the Universe.

https://fileviezdotcom.files.wordpress.com/2018/10/arxiv.pdf

John T. Giblin Jr, James B. Mertens, Glenn D. Starkman, Chi Tian

Standard cosmological models rely on an approximate treatment of gravity, utilizing solutions of the linearized Einstein equations as well as physical approximations. In an era of precision cosmology, we should ask: are these approximate predictions sufficiently accurate for comparison to observations, and can we draw meaningful conclusions about properties of our Universe from them? In this work we examine the accuracy of linearized gravity in the presence of collisionless matter and a cosmological constant utilizing fully general relativistic simulations. We observe the gauge-dependence of corrections to linear theory, and note the amplitude of these corrections. For perturbations whose amplitudes are in line with expectations from the standard $\Lambda$CDM model, we find that the full, general relativistic metric is well-described by linear theory in Newtonian and harmonic gauges, while the metric in comoving-synchronous gauge is not. For the largest observed structures in our Universe, our results suggest that corrections to linear gravitational theory can reach or surpass the percent-level.

Kevin Spencer McCarthy, Zheng Zheng, Hong Guo

The large-scale redshift-space distortion (RSD) in galaxy clustering can probe $f\sigma_8$, a combination of the cosmic structure growth rate and the matter fluctuation amplitude, which can constrain dark energy models and test theories of gravity. While the RSD on small scales (e.g. a few to tens of $h^{-1}{\rm Mpc}$) can further tighten the $f\sigma_8$ constraints, galaxy assembly bias, if not correctly modelled, may introduce systematic uncertainties. Using a mock galaxy catalogue with built-in assembly bias, we perform a preliminary study on how assembly bias may affect the $f\sigma_8$ inference. We find good agreement on scales down to 8--9$h^{-1}{\rm Mpc}$ between a $f\sigma_8$ metric from the redshift-space two-point correlation function with the central-only mock catalogue and that with the shuffled catalogue free of assembly bias, implying that $f\sigma_8$ information can be extracted on such scales even with assembly bias. We then apply the halo occupation distribution (HOD) and three subhalo clustering and abundance matching (SCAM) models to model the redshift-space clustering with the mock. Only the SCAM model based on $V_{\rm peak}$ (used to create the mock) can reproduce the $f\sigma_8$ metric, and the other three could not. However, the $f\sigma_8$ metrics determined from central galaxies from all the models are able to match the expected one down to 8$h^{-1}{\rm Mpc}$. Our results suggest that halo models with no or incorrect assembly bias prescription could still be used to model the RSD down to scales of $\sim 8 h^{-1}{\rm Mpc}$ to tighten the $f\sigma_8$ constraint, with a sample of central galaxies or with a flexible satellite occupation prescription.

R. Yunis, C. R. Argüelles, N. E. Mavromatos, A. Moliné, A. Krut, J. A. Rueda, R. Ruffini

We calculate the most stringent constraints up to date on the parameter space for sterile neutrino warm dark matter models possessing a radiative decay channel into X-rays. These constraints arise from the X-ray flux observations from the Galactic center (central parsec), taken by the XMM and NuSTAR missions. We compare the results obtained from using different dark matter density profiles for the Milky Way, such as NFW, Burkert or Einasto, to that produced by the Ruffini-Arg\"uelles-Rueda (RAR) fermionic model, which has the distinct feature of depending on the particle mass. We show that due to the novel core-halo morphology present in the RAR profile, the allowed particle mass window is narrowed down to $m_s\sim 10-15$ keV, when analyzed within the $\nu$MSM sterile neutrino model. We further discuss on the possible effects in the sterile neutrino parameter-space bounds due to a self-interacting nature of the dark matter candidates.

Metin Gurses, Bayram Tekin

The classical double copy idea relates some solutions of Einstein's theory with those of gauge and scalar field theories. We study the Kerr-Schild-Kundt (KSK) class of metrics in $d$-dimensions in the context of possible new examples of this idea. We first show that it is possible to solve the Einstein-Yang-Mills system exactly using the solutions of a Klein-Gordon type scalar equation when the metric is the $pp$-wave metric which is the simplest member of the KSK class. In the more general KSK class, the solutions of a scalar equation also solve the Yang-Mills, Maxwell and Einstein-Yang-Mills-Maxwell equations exactly albeit with a null fluid source. Hence in the general KSK class, the double copy correspondence is not as clean-cut as in the case of the $pp$-wave. In our treatment all the gauge fields couple to dynamical gravity, and are not treated as test fields. We also briefly study G\"{o}del type metrics along the same lines.