Constraints and cosmography of $\Lambda$CDM in presence of viscosity

TL;DR

This paper investigates viscous dark matter in the universe, constraining model parameters with observational data, and finds that viscosity can influence cosmographic parameters while supporting the standard Lambda-CDM model within uncertainties.

Contribution

It introduces a viscous fluid model for dark matter with polynomial viscosity dependence and constrains it using Bayesian analysis with recent cosmological data.

Findings

Viscous models are supported equally well as LCDM by OHD and SNIa data.

Cosmographic parameters are consistent with LCDM within 3 sigma.

Viscosity parameters significantly affect the universe's acceleration-deceleration transition.

Abstract

In this work, we study two scenarios of the Universe filled by a perfect fluid following the traditional dark energy and a viscous fluid as dark matter. In this sense, we explore the simplest case for the viscosity in the Eckart formalism, a constant, and then, a polynomial function of the redshift. We constrain the phase-space of the model parameters by performing a Bayesian analysis based on Markov Chain Monte Carlo method and using the latest data of the Hubble parameter (OHD), Type Ia Supernovae (SNIa) and Strong Lensing Systems. The first two samples cover the region $0.01<z<2.36$. Based on AIC, we find equally support of these viscous models over Lambda-Cold Dark Matter (LCDM) taking into account OHD or SNIa. On the other hand, we reconstruct the cosmographic parameters ($q,j,s,l$) and find good agreement to LCDM within up to $3\sigma$ CL. Additionally, we find that the cosmographic parameters and the acceleration-deceleration transition are sensible to the parameters related to the viscosity coefficient, making of the viscosity an interesting physical mechanism to modified them.