Tuesdays 10:30 - 11:30 | Fridays 11:30 - 12:30
Showing votes from 2018-10-12 12:30 to 2018-10-16 11:30 | Next meeting is Tuesday Jul 22nd, 10:30 am.
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
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.
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.
In this letter we use the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence to establish a set of old conjectures about symmetries in quantum gravity. These are that no global symmetries are possible, that internal gauge symmetries must come with dynamical objects that transform in all irreducible representations, and that internal gauge groups must be compact. These conjectures are not obviously true from a bulk perspective, they are nontrivial consequences of the non-perturbative consistency of the correspondence. More details of and background for these arguments are presented in an accompanying paper.