General Relativity and Quantum Cosmology (gr-qc)

Abstract: In this work, we have studied the quasinormal modes and greybody factors of AdS/dS Reissner-Nordstr\"om black hole surrounded by quintessence field in Rastall gravity. The violation of energy-momentum conservation has a non-linear effect on the quasinormal modes. With an increase in the black hole charge, both real part of quasinormal modes i.e. oscillation frequency of ring-down Gravitational Waves (GWs) and damping or decay rate of GWs increase non-linearly. A similar observation is made for the black hole structural parameter also, however in this case the variation is almost linear. In the case of greybody factors also, we observed that both the parameters have similar impacts. With an increase in these parameters, greybody factors decrease. Our study suggests that the presence of a surrounding quintessence field may shadow the existence of black hole charge in such black hole configurations.

Abstract: In order to reconcile the wave-function collapse in quantum mechanics with the finiteness of signals' propagation in general relativity, we delve into a stochastic version of the Ricci flow and study its non-relativistic limit in presence of matter. We hence derive the Di\'osi-Penrose collapse model for the wave-function of a quantum gas. The procedure entails additional parameters with respect to phenomenological models hitherto accounted for, including the temperature of the gas and the cosmological constant, in turn related to the stochastic gravitational noise responsible for the collapse.

Abstract: We introduce GWDALI, a new Fisher-matrix, python based software that computes likelihood gradients to forecast parameter-estimation precision of arbitrary network of terrestrial gravitational wave detectors observing compact binary coalescences. The main new feature with respect to analogous software is to assess parameter uncertainties beyond Fisher-matrix approximation, using the derivative approximation for Likelihood (DALI). The software makes optional use of the LSC algorithm library LAL and the stochastic sampling algorithm Bilby, which can be used to perform Monte-Carlo sampling of exact or approximate likelihood functions. As an example we show comparison of estimated precision measurement of selected astrophysical parameters for both the actual likelihood, and for a variety of its derivative approximations, which turn out particularly useful when the Fisher matrix is not invertible.