Speaker
Description
The history of the expansion of the universe encodes critical information about its composition and the underlying physics that governs cosmic evolution. In this work, we investigate the role that viscous cosmic fluids may play in setting the background dynamics of the universe within the FLRW framework. By extending the standard model of cosmology to include bulk viscosity in the cosmic fluid, we discuss how dissipative effects can modify the Hubble expansion rate $H(z)$, the deceleration parameter $q(z)$, and the effective equation of state. We analyze two models in parallel: (i) the standard non-viscous $\Lambda$CDM case and (ii) a viscous fluid model whose evolution follows the causal Israel-Stewart formalism, which guarantees thermodynamic consistency and stability of the models. We constrain both models using a combined dataset consisting of Cosmic Chronometers (CC), Baryon Acoustic Oscillations (BAO), Type Ia Supernovae (Pantheon+), and Planck 2018 CMB distance priors. Our analysis shows that viscosity can contribute significantly to the alleviation of late-time cosmic tension, such as the $H_0$ and $\sigma_8$ discrepancies, while it naturally gives rise to an accelerated expansion without relying on a cosmological constant. Comparative statistical analyses using $\chi^2$ minimization and information criteria indicate that the viscous scenario can offer a competitive or even better fit to current observations. These results indicate that bulk viscosity can potentially offer a unified description of cosmic acceleration that is consistent with observational bounds.
| Stream | Science or Engineering |
|---|