The effective Tolman temperature in curved spacetimes

TL;DR

This paper reviews the effective Tolman temperature in curved spacetimes, resolving conflicts in black hole thermodynamics, and applies it to cosmology, showing it explains initial radiation energy density in warm inflation.

Contribution

It introduces a consistent framework for the effective Tolman temperature, reconciling divergences at horizons and applying it to black hole and cosmological scenarios.

Findings

Effective Tolman temperature remains finite at horizons, restoring the equivalence principle.

The firewall in evaporating black holes is linked to the negative ingoing flux, compatible with the atmosphere picture.

The initial radiation energy density in warm inflation can be explained using the effective Tolman temperature.

Abstract

We review a recently proposed effective Tolman temperature and present its applications to various gravitational systems. In the Unruh state for the evaporating black holes, the free-fall energy density is found to be negative divergent at the horizon, which is in contrast to the conventional calculations performed in the Kruskal coordinates. We resolve this conflict by invoking that the Kruskcal coordinates could be no longer proper coordinates at the horizon. In the Hartle-Hawking-Israel state, despite the negative finite proper energy density at the horizon, the Tolman temperature is divergent there due to the infinite blueshift of the Hawking temperature. However, a consistent Stefan-Boltzmann law with the Hawking radiation shows that the effective Tolman temperature is eventually finite everywhere and the equivalence principle is surprisingly restored at the horizon. Then, we also show that the firewall necessarily emerges out of the Unruh vacuum, so that the Tolman temperature in the evaporating black hole is naturally divergent due to the infinitely blueshifted negative ingoing flux crossing the horizon, whereas the outgoing Hawking radiation characterized by the effective Tolman temperature indeed originates from the quantum atmosphere, not just at the horizon. So, the firewall and the atmosphere for the Hawking radiation turn out to be compatible, once we discard the fact that the Hawking radiation in the Unruh state originates from the infinitely blueshifted outgoing excitations at the horizon. Finally, as a cosmological application, the initial radiation energy density in warm inflation scenarios has been assumed to be finite when inflation starts. We successfully find the origin of the non-vanishing initial radiation energy density in the warm inflation by using the effective Tolman temperature.