Asymptotic behavior of the warm inflation scenario with viscous pressure

TL;DR

This paper studies the long-term behavior of warm inflation models with viscous effects, showing conditions for scaling solutions and how dissipative terms influence matter depletion and inflation duration.

Contribution

It provides a classification of asymptotic behaviors in warm inflation with viscous pressure, highlighting the role of decay rates and potential steepness in late-time dynamics.

Findings

Scaling solutions occur when the decay rate is proportional to the Hubble rate.

Dissipative effects extend the duration of inflation by reducing matter depletion.

The matter-radiation temperature follows a power-law dependence on the scale factor.

Abstract

We analyze the dynamics of models of warm inflation with general dissipative effects. We consider phenomenological terms both for the inflaton decay rate and for viscous effects within matter. We provide a classification of the asymptotic behavior of these models and show that the existence of a late-time scaling regime depends not only on an asymptotic behavior of the scalar field potential, but also on an appropriate asymptotic behavior of the inflaton decay rate. There are scaling solutions whenever the latter evolves to become proportional to the Hubble rate of expansion regardless of the steepness of the scalar field exponential potential. We show from thermodynamic arguments that the scaling regime is associated to a power-law dependence of the matter-radiation temperature on the scale factor, which allows a mild variation of the temperature of the matter/radiation fluid. We also show that the late time contribution of the dissipative terms alleviates the depletion of matter, and increases the duration of inflation.