Thermodynamics of Decaying Vacuum Cosmologies

TL;DR

This paper explores the thermodynamic properties of vacuum decay in cosmology, showing how energy transfer affects temperature and spectrum, and discusses implications for cosmological models with photon creation.

Contribution

It introduces a covariant framework for thermodynamics in decaying vacuum cosmologies, deriving temperature laws and spectral forms consistent with energy flow and entropy conservation.

Findings

Energy density and photon number density scale with temperature as T^4 and T^3.

A generalized Planckian spectrum remains invariant during decay.

Implications for vacuum decay models and adiabatic photon creation are discussed.

Abstract

The thermodynamic behavior of vacuum decaying cosmologies is investigated within a manifestly covariant formulation. Such a process corresponds to a continuous irreversible energy flow from the vacuum component to the created matter constituents. It is shown that if the specific entropy per particle remains constant during the process, the equilibrium relations are preserved. In particular, if the vacuum decays into photons, the energy density $\rho$ and average number density of photons $n$ scale with the temperature as $\rho \sim T^{4}$ and $n \sim T^{3}$. The temperature law is determined and a generalized Planckian type form of the spectrum, which is preserved in the course of the evolution, is also proposed. Some consequences of these results for decaying vacuum FRW type cosmologies as well as for models with ``adiabatic'' photon creation are discussed.