Constraining a bulk viscous matter-dominated cosmological model using SNe Ia, CMB and LSS

TL;DR

This paper tests a bulk viscous matter cosmological model against multiple observational data sets, finding it incompatible with the data and thus ruling it out as a viable explanation for the universe's accelerated expansion.

Contribution

The study constrains a bulk viscous matter model using SNe Ia, CMB, and BAO data, providing a comprehensive test of its viability against current cosmological observations.

Findings

Model violates the Second Law of Thermodynamics when all tests are combined.

Predicts a low Hubble constant of about 53 km/sec/Mpc.

Fits poorly to the combined data with a high chi-squared value.

Abstract

We present and constrain a cosmological model which component is a pressureless fluid with bulk viscosity as an explanation for the present accelerated expansion of the universe. We study the particular model of a constant bulk viscosity coefficient \zeta_m. The possible values of \zeta_m are constrained using the cosmological tests of SNe Ia Gold 2006 sample, the CMB shift parameter R from the three-year WMAP observations, the Baryon Acoustic Oscillation (BAO) peak A from the Sloan Digital Sky Survey (SDSS) and the Second Law of Thermodynamics (SLT). It was found that this model is in agreement with the SLT using only the SNe Ia test. However when the model is submitted to the three cosmological tests together (SNe+CMB+BAO) the results are: 1.- the model violates the SLT, 2.- predicts a value of H_0 \approx 53 km sec^{-1} Mpc^{-1} for the Hubble constant, and 3.- we obtain a bad fit to data with a \chi^2_{min} \approx 400 (\chi^2_{d.o.f.} \approx 2.2). These results indicate that this model is ruled out by the observations.