Study of warm inflation using irreversible thermodynamical description within Rastall gravity

Abstract

This manuscript aims to study warm inflation via “irreversible thermodynamics of open systems” with matter creation/decay within Rastall theory of gravity. Interacting scalar field and radiation are assumed to be the components of cosmological fluid in spatially flat FRW universe model. Considering early universe as an open system, and implementing the thermodynamics along with the dynamical equations in Rastall gravity on the interacting cosmological fluid leads to modify the standard formalism of warm inflationary model, including the creation(decay) pressure, which is considered as part of the energy–momentum tensor explicitly. The analysis is done using constant as well as Higgs potential. Under slow-roll approximation and introducing some dimensionless variables, numerical solutions of the thermodynamical equations (scale factor, number of scalar field particles, energy densities of scalar field and radiation and temperature) are obtained and represented graphically. For appropriate set of initial conditions, these results depict the phase transition from acceleration to deceleration phase. Using obtained solutions, we calculate inflationary observable like “slow-roll parameters, number of e-folds, scalar/tensor power spectra, scalar/tensor spectral indices and tensor-to-scalar ratio”. By constraining the free model parameters, the theoretical predictions of the under lying model are compared with the Planck-2018 data.