Amplification of cosmological inhomogeneities by the QCD transition - art.no. 043517.

The cosmological QCD transition affects primordial density perturbations. I f the QCD transition is first order, the sound speed vanishes during the tr ansition and density perturbations fall freely. For scales below the Hubble radius at the transition the primordial Harrison-Zel'dovich spectrum of de nsity fluctuations develops large peaks and dips. These peaks grow with wav e number for both the hadron-photon-lepton fluid and for cold dark matter. At the horizon scale the enhancement is small. This by itself does not lead to the formation of black holes at the QCD transition. The peaks in the ha dron-photon-lepton fluid an wiped out during neutrino decoupling. For cold dark matter that is kinetically decoupled at the QCD transition (e.g., axio ns or primordial black holes) these peaks lead to the formation of CDM clum ps of masses 10(-20)M(.)<M-clump< 10(-10) M-.. [S0556-2821(99)05702-1].