Thermal condensate structure and cosmological energy density of the Universe

TL;DR

This paper investigates the thermal vacuum condensate of scalar and fermion fields at cosmic background temperatures, linking vacuum expectation values to cosmic energy density and exploring the structure of thermal radiation.

Contribution

It introduces a formal analysis of thermal vacuum condensates at cosmic background temperatures, connecting quantum field theory with cosmological energy density estimates.

Findings

Vacuum expectation values reproduce CMB energy density and pressure.

Neutrino thermal states align with neutrino mass bounds.

Axion-like particles contribute to the universe's energy with masses around 10^{-4} eV.

Abstract

The aim of this paper is the study of thermal vacuum condensate for scalar and fermion fields. We analyze the thermal states at the temperature of the cosmic microwave background (CMB) and we show that the vacuum expectation value of the energy momentum tensor density of photon fields reproduces the energy density and pressure of the CMB. We perform the computations in the formal framework of the thermo field dynamics. We also consider the case of neutrinos and thermal states at the temperature of the neutrino cosmic background. Consistency with the estimated lower bound of the sum of the active neutrino masses is verified. In the boson sector, non trivial contribution to the energy of the universe is given by particles of masses of the order of $10^{-4}eV$ compatible with the ones of the axion-like particles. The fractal self-similar structure of the thermal radiation is also discussed and related to the coherent structure of the thermal vacuum.