C. Schmid et al., PEAKS ABOVE THE HARRISON-ZELDOVICH SPECTRUM DUE TO THE QUARK-GLUON TOHADRON TRANSITION, Physical review letters, 78(5), 1997, pp. 791-794
The quark-gluon to hadron transition affects the evolution of cosmolog
ical perturbations. If the phase transition is first order, the sound
speed vanishes during the transition, and density perturbations fall f
reely. This distorts the primordial Harrison-Zel'dovich spectrum of de
nsity fluctuations below the Hubble scale at the transition. Peaks are
produced, which grow, at most, linearly in wave number, both for the
hadron-photon-lepton fluid and for cold dark matter. For cold dark mat
ter which is kinetically decoupled well before the QCD transition, clu
mps of masses below 10-(10)M(circle dot), an produced.