Thermal particle production in a contracting and expanding universe without singularity

Abstract

The creation of massive spin-0 particles described by the conformally coupled Klein-Gordon equation in a 3-flat Robertson-Walker universe d s 2 = R 2( η)(d η 2 − d x 2 − d y 2 − d z 2 with contraction-expansion law R 2 = b 2 η 2 + R 2 0 for −∞ < η < +∞ is studied. It represents a time-symmetric universe for which the singularity is avoided. Particles are created in the out-region with a nonrelativistic thermal spectrum with temperature T = b(2 πR 2 k B ) −1 and chemical potential μ = −1 2 mR 2 0R −2 . The latter implies an expotential damping for large m.