We study the late-time cosmological dynamics of a spatially flat FLRW universe in the framework of f(Q) gravity, where Q denotes the nonmetricity scalar. The matter sector is modeled as a bulk viscous fluid with a free equation-of-state parameter γ, allowing for a generalized description of cosmic matter beyond the standard dust approximation. We derive the background evolution equations and analyze the resulting expansion history. The model parameters are constrained using a combination of observational datasets, including cosmic chronometers (CC), baryon acoustic oscillations from DESI DR2, and Type~Ia supernovae (GRBs and Union3). Using the best-fit parameters, we further employ the statefinder and Om(z) diagnostics to distinguish the viscous f(Q) scenario from the standard ΛCDM model. In addition, we examine the evolution of the deceleration parameter, which exhibits a transition from an early decelerated phase to the current accelerated expansion, and analyze the effective equation of state behavior. Our results show that bulk viscosity within f(Q) gravity provides a viable and observationally consistent description of late-time cosmic acceleration.
@article{arxiv.2602.16757,
title = {Observational constraints on viscous free-$\gamma$ fluid in $f(Q)$ gravity},
author = {Simran Arora and Sai Swagat Mishra and P. K. Sahoo},
journal= {arXiv preprint arXiv:2602.16757},
year = {2026}
}