Day 1482

Monday.

1810.01847
Black Hole entropy and soft hair
Halo, Hawking, Perry, Strominger

A set of infinitesimal Virasoro_L (*) Virasoro_R diffeomorphisms are presented which act non-trivially on the horizon of a generic Kerr black hole with spin J.  The covariant phase space formalism provides a formula for the Virasoro charges as surface integrals on the horizon.  Integrability and associativity of the charge algebra are shown to require the inclusion of Wald-Zoupas' counterterms.  A counter term satisfying the known consistency requirement is constructed and yields central charges c_L=c_R=12J.  Assuming the existence of a quantum Hilbert space on which these charges generate the symmetries, as well as the applicability of the Cardy formula, the central charges reproduce the macroscopic area-entropy law for generic Kerr black holes.


1810.05183
The effects of galaxy assembly bias on the inference of growth rate from redshift-space distortions
McCarthy, Zheng, Guo

The large scale z-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 DE models and test theories of gravity.  While the RSD on small scales (e.g. a few to tends of h^{-1} Mpc) can further tighten the f sigma_8 constraints, galaxy assembly bias, if not correctly modeled, may introduce systematic uncertainties.  Using a mock galaxy catalogue with built-in assembly bias, perform a preliminary study on how assembly bias may affect the f sigma_8 inference.  Find good agreement on scales down to 8-9 h^{-1} Mpc between a f sigma_8 metric from the z-space 2pt 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.  Then apply the halo occupation distribution (HOD) and 3 sub halo clustering and abundance matching (SCAM) models to model the z-space clustering with the mock.  Only the SCAM model based on v_peak (used to create the mock) can reproduce the f sigma_8 metric, and the other 3 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} Mpc.  The results suggest that halo models with no or incorrect assembly bias prescription could still be used to model the RSD down to scales of ~8 h^{-1} Mpc to tighten the f sigma_8 constraint, with a sample of central galaxies or with a flexible satellite occupation prescription.


1810.05225
Inherently stable effective field theory for dark energy and modified gravity
Lombriser, et al

The growing wealth of cosmo observations places increasingly more stringent constraints on DE and alternative gravity models.  Particularly successful in efficiently probing the vast model space has been the effective field theory of dark energy and modified gravity, providing a unified framework for generalized cosmological predictions.  However, the optimal parameterization of the free time-dependent function inherent to the formalism is still unresolved.  It should respect a multitude of requirements, ranging from simplicity, generality and representativity of known theories to computational efficiency.  But in particular, for theoretical soundness, the parameter space should adhere to strict stability requirements.  Recently proposed an inherently stable effective field theory with physical basis of Planck mass evolution, sound speed of the scalar field fluctuations, kinetic coefficient, and background expansion, which covers Horndeski models with luminal speed of gravity.  Here, devise a parameterization of these basis functions that can straightforwardly be configured to evade theoretical pathologies such as ghost or gradient instabilities or to accommodate further theoretical priors such as subliminal scalar sound speed.  The parameterisation is simple yet general, conveniently represents a broad range of known DE and gravitational theories, and with a simple additional approximation can be rendered numerically highly efficient.  Finally, by operating in the new basis, show that there are no general limitations from stability requirements on the current values that can be assumed by the phenomenological modification of the Poisson equation and the gravitational slip besides the exclusion of anti-gravity.  The inherently stable effective field theory is ready for implementation in parameter estimation analyses employing linear cosmological observations.