Dissipative cosmology and the nature of dark energy: insights from bulk viscosity with DESI DR2 observations

Abstract

We study cosmological models in which the late time accelerated expansion is driven by a bulk viscous dark energy fluid, motivated by the possibility that dissipative processes in the cosmic medium can generate an effective negative pressure without requiring a cosmological constant. Restricting our analysis to the homogeneous background evolution, we consider both minimally and non-minimally coupled viscous scenarios and analyze them using Type Ia supernovae, DESI DR2 baryon acoustic oscillation measurements, and the Planck 2018 cosmic microwave background data. We show that bulk viscosity naturally gives rise to dynamical dark energy behavior and can provide an alternative description of the observed expansion history. Compared to \(\Lambda \)CDM, we find the interacting non–minimal model produces a marginal preference over \(\Lambda \)CDM using different evidence estimations. The results demonstrate that bulk-viscous dark energy remains an observationally viable phenomenological framework at the background level however some viscous parameters remain prior-sensitive.