Little inflation at the cosmological QCD phase transition

Abstract

We reexamine the recently proposed ``little inflation'' scenario that allows for a strong first-order phase transition of QCD at non-negligible baryon number in the early Universe and its possible observable consequences. The scenario is based on the assumptions of a strong mechanism for baryogenesis and a quasistable QCD-medium state which triggers a short inflationary period of inflation diluting the baryon asymmetry to the value observed today. The cosmological implications are reexamined, namely, effects on primordial density fluctuations up to dark matter mass scales of ${M}_{\mathrm{max}}\ensuremath{\sim}1{M}_{\ensuremath{\bigodot}}$, change in the spectral slope up to ${M}_{\mathrm{max}}\ensuremath{\sim}{10}^{6}{M}_{\ensuremath{\bigodot}}$, production of seeds for the present galactic and extragalactic magnetic fields, and a gravitational wave spectrum with a peak frequency around ${\ensuremath{\nu}}_{\mathrm{peak}}\ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }\text{ }\mathrm{Hz}$. We discuss the issue of nucleation in more detail and employ a chiral effective model of QCD to study the impact on small scale structure formation.