10th International Conference on Gravitation and Cosmology: New Horizons and Singularities in Gravity (ICGC 2023)

Signature flip in deceleration parameter: A thermodynamic phase transition?

Not scheduled

15m

IIT Guwahati

Oral Cosmology Cosmology

Speaker

Tanima Duary (INDIAN INSTITUTE OF SCIENCE EDUCATION AND RESEARCH KOLKATA)

Description

Under the assumption of thermal equilibrium between the horizon and the fluid inside, we conducted a thermodynamic stability analysis on a model designed to mimic the characteristics of the $\mathrm{\Lambda }$CDM model, which is the prevailing framework for portraying the cosmic acceleration. The scale factor for this model is defined as $a\sim {\sinh }^{2/3}(t/t_0)$. The Hayward-Kodama temperature is opted for the evolving apparent horizon. The outcome of this analysis yielded a remarkable finding: the thermal capacity exhibited a negative value and a lack of thermodynamic stability within the cosmic matter enclosed by the horizon.

The significance of this study lies in the result indicating that the matter content experiences a phase transition precisely at the value of $z$ where the Universe undergoes a transition from decelerated expansion to an accelerated one. Notably, this phase transition manifests characteristics akin to those of a second-order phase transition, as indicated by the discontinuity in heat capacity at constant volume ($C_V$). The deceleration parameter ($q$) serves as the order parameter and solidifies this correlation.