# Cosmological test on viscous bulk models using Hubble Parameter measurements and type Ia Supernovae data

## TL;DR

This study investigates viscous bulk models of the universe using observational data to constrain parameters and compare their behavior with the standard LCDM model, finding that these viscous models are not favored by current data.

## Contribution

It introduces polynomial and hyperbolic bulk viscosity models into cosmology and constrains their parameters using observational data, providing a comparison with the LCDM model.

## Key findings

- Viscous models are not supported over LCDM by data.
- Current deceleration parameter q0 around -0.6 to -0.7.
- Jerk parameter j0 varies significantly between models.

## Abstract

From a phenomenological point of view, we analyze the dynamics of the Universe at late times by introducing a polynomial and hyperbolic bulk viscosity into the Einstein field equations respectively. We constrain their free parameters using the observational Hubble parameter data and the Type Ia Supernovae dataset to reconstruct the deceleration $q$ and the jerk $j$ parameters within the redshift region $0<z<2.5$. At current epochs, we obtain $q_0 = -0.680^{+0.085}_{-0.102}$ and $j_0 = 2.782^{+1.198}_{-0.741}$ for the polynomial model and $q_0 = -0.539^{+0.040}_{-0.038}$ ($-0.594^{+0.056}_{-0.056}$) and $j_0 = 0.297^{+0.051}_{-0.050}$ ($1.124^{+0.196}_{-0.178}$) for the tanh (cosh) model. Furthermore, we explore the statefinder diagnostic that gives us evident differences with respect to the concordance model (LCDM). According to our results this kind of models is not supported by the data over LCDM.