Big bang nucleosynthesis and entropy evolution in f(R, T) gravity

Abstract

The present article is devoted to constraining the model parameter $\chi$ for the $f(R,T)= R + \chi T$ gravity model by employing the constraints coming from big bang nucleosynthesis. We solve the field equations and constrain $\chi$ in the range $-0.14 \kappa ^{2} \le \chi \le 0.84 \kappa ^{2}$ (where $\kappa ^{2} = \frac{8 \pi G}{c^{4}}$) from the primordial abundances of light elements such as helium-4, deuterium and lithium-7. We found the abundances of helium-4 and deuterium agree with theoretical predictions; however, the lithium problem persists for the f(R, T) gravity model. We also investigate the evolution of entropy for the constrained parameter space of $\chi$ for the radiation and dust universe. We report that entropy is constant when $\chi = 0$ for the radiation-dominated universe, whereas for the dust universe, entropy increases with time. We finally use the constraints to show that $\chi$ has a negligible influence on the cold dark matter annihilation cross section.