Viscous attenuation of gravitational waves propagating through an inhomogeneous background

TL;DR

This paper studies how matter inhomogeneities and viscosity of the cosmic fluid affect gravitational wave observations in the late Universe, highlighting the importance of viscous attenuation in precision parameter estimation.

Contribution

It introduces a model combining inhomogeneous matter distribution and viscous cosmic fluid to analyze gravitational wave amplitude variations and their observational implications.

Findings

Viscous attenuation causes significant deviations in gravitational wave amplitude.

Inhomogeneities and viscosity jointly influence redshift-dependent GW signals.

Viscosity effects are crucial for accurate gravitational wave parameter measurements.

Abstract

We consider the propagation of gravitational waves in the late-time Universe in the presence of matter distribution inhomogeneities, and we also consider the cosmic fluid to be viscous. In this work, we investigate the cumulative effect of inhomogeneities and viscosity of the cosmic-fluid on the observables associated with the sources of the gravitational waves. Employing Buchert's averaging procedure in the backreaction framework, we consider a model of spacetime in which matter is distributed in-homogeneously across space. Using the modified redshift versus distance relation, through the averaging process in the context of the model, we study the variation of the redshift-dependent part of the observed gravitational wave amplitude for different combinations of our model parameters while simultaneously considering damping of the gravitational wave amplitude due to viscosity of the cosmic-fluid. Then, we investigate the differences occurring in the variation of the redshift-dependent part of the observed gravitational wave amplitude due to consideration of viscous attenuation. We show that there are significant deviations after the inclusion of viscous attenuation in our analysis, depending on the chosen value of the coefficient of viscosity. Our result signifies the importance of the effect of viscosity, within the model of an inhomogeneous Universe, on precision measurements of parameters of compact-binary sources of gravitational waves.