Observational Analysis of Exponentially Decaying Viscous Cosmology in f(Q,C)$f(Q,C)$ Gravity

Abstract In this work, the effects of viscosity in gravity are investigated by considering the model with an new exponential bulk viscosity of the form . The Hubble parameter is derived in terms of redshift and constrain the model parameters using observational datasets, including CC, DESI DR2 BAO and Pantheon+ datasets, via the MCMC approach. The best‐fit values of the parameters are obtained and the evolution of cosmological parameters is analyzed. The results indicate a transition from a decelerated to an accelerated expansion phase, with the present deceleration parameter value for the joint dataset. The equation of state parameter approaches at late times and the SEC is violated, supporting cosmic acceleration. The statefinder analysis shows that the model evolves from a Chaplygin gas phase to quintessence and finally converges to . Additionally, the impact of viscosity is examined, showing that its influence is significant in the early Universe but diminishes over time. These findings suggest that viscosity plays a crucial role in cosmic evolution within gravity, providing a viable alternative framework for late‐time acceleration.