Effective chemical potential and its phenomenological implications for the Hubble parameter

Abstract

In cosmological models, the Hubble parameter is determined by the time evolution of the scale factor, and current observations reveal a persistent tension between its values inferred from different probes, such as Cepheid variable stars and the cosmic microwave background. Within Tsallis' statistical framework, we identify two distinct definitions of fugacity associated with relativistic and non-relativistic regimes. For the non-relativistic sector, we introduce an effective chemical potential and establish its connection with the Gibbs free energy. We then explore a phenomenological correspondence between this effective chemical potential and an Unruh-like temperature associated with accelerated trajectories in an expanding cosmological background. As an application, we derive an effective expression for the Hubble parameter that includes a statistics-dependent contribution arising from the non-relativistic matter sector. This contribution suggests that non-Gaussian statistical effects, when consistently incorporated in the non-relativistic matter sector, can enhance the sensitivity of the expansion rate to underlying thermostatistical assumptions, achieving a substantial increase in sensitivity by approximately ten orders of magnitude when compared with previous relativistic constructions that investigated, at a phenomenological level, the discrepancy observed in current determinations of the Hubble constant.