Dynamical Evolution and Graceful Exit in Quartic Warm Inflation

Abstract

In this study, we investigate the full nonlinear dynamics of warm inflation driven by the quartic inflaton potential, avoiding any simplifying approximations. The thermal backreaction is incorporated through a dissipation coefficient that depends linearly on the temperature, and the model parameters are chosen to remain consistent with Planck observational constraints. By numerically integrating the complete set of three coupled, nonlinear differential equations that describe the evolution of the inflaton field, radiation energy density, and background expansion, we obtain an exact description of the system's dynamics. Our results reveal that, while transition to radiation domination is suppressed in the weak regime, the strong dissipative regime leads to a smooth and natural transition to a hot, radiation-dominated Universe, thereby confirming graceful-exit within warm inflation in the quartic scenario. The reheating temperature is extracted directly from the nonlinear evolution of warm inflation, yielding a temperature of approximately 10^13 GeV at the end of inflation, which cools to about 10^12 GeV near radiation-inflaton equality, whence the Universe transitions into a radiation-dominated era.