Thermal particle production in a radiation dominated Robertson-Walker universe

Abstract

Creation of massive spin-¹/₂ particles in a 3-flat Robertson-Walker universe with expansion law R approximately t^1/2 (radiation dominated universe) is studied with Fock space methods. The universe is thereby completed in 'passing through the singularity' by a time-symmetric (mirror-like) contracting universe preceding the singularity. The respective procedure to do so for Dirac test fields (conformal method) is discussed in detail. For the asymptotic in- and out-regions a WKB particle interpretation is applied. It is found that particles are created with a non-relativistic thermal spectrum. The expressions for the number density, energy density and pressure of the created particles confirm this result (equation of state). The study of the development in time of the creation process shows that 99% of the particles created all together are created at about the Compton time.