Amplification of cosmological inhomogeneities by the QCD transition

Abstract

The cosmological QCD transition affects primordial density perturbations. If the QCD transition is first order, the sound speed vanishes during the transition and density perturbations fall freely. For scales below the Hubble radius at the transition the primordial Harrison-Zel'dovich spectrum of density fluctuations develops large peaks and dips. These peaks grow with wave 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 hadron-photon-lepton fluid are wiped out during neutrino decoupling. For cold dark matter that is kinetically decoupled at the QCD transition ͑e.g., axions or primordial black holes͒ these peaks lead to the formation of CDM clumps of masses 10 Ϫ20 M ᭪ ϽM clump Ͻ10 Ϫ10 M ᭪ . ͓S0556-2821͑99͒05702-1͔PACS number͑s͒: 98.80. Cq, 12.38.Mh, 95.35.ϩd †

Fluctuations of the gravitational field generated by a random population of extended substructures

“…Bertone et al 2005) the cut-off is placed on planet-size mass scales, M1 ∼ 10 −6 M (e.g. Schmid et al 1999;Hofmann et al 2001;Green et al 2005;Loeb & Zaldarriaga 2005;Diemand et al 2005), which leads to one of the most striking predictions from the cold dark matter (CDM) paradigm, namely the existence of a very large number of self-gravitating "microhaloes" with subsolar masses devoid of baryons (i.e. 'dark').…”

Phase transitions in the early and the present Universe: from the big bang to heavy ion collisions

“…A more detailed analysis of the possibility of primordial black hole formation and the ensuing density fluctuations has been provided recently [29]. The results of this reference, based on approximate or lattice EoS seem to lead to a less likely scenario for solar mass primordial black hole formation, but to an enhancement in the clumping of cold dark matter (CDM).…”

“…• Primordial Black Holes: [28,29] An important aspect of a first order phase transition (with only one globally conserved quantity, such as baryon number) is that during the coexistence or mixed phase of QGP and hadron gas, the Gibbs construction determines that the phase transition occurs at constant pressure (as well as temperature). If the pressure is constant, then the (adiabatic) speed of sound vanishes and there are no restoring pressure waves.…”

Relics of cosmological quark-hadron phase transition

“…Only the fluctuations with the comoving wavenumber k > ∼ 10 4 k H can retain their horizon crossing amplitude δ H [9], where k H is the comoving wavenumber of the fluctuation which enters the horizon at the transition. During the whole time of the transition, the sound velocity transition amplify the amplitudes of the subhorizon fluctuations with δ H and k upto…”

“…The amplified fluctuations may produce nonlinear lumps which are decoupled from the expansion of the background universe. If the decoupled lumps were hadronic, however, they would be washed out by neutrino damping [8] before the big-bang nucleosynthesis era [5,9], so could not give any significant effect on dark matter problem as well as the inhomogeneous big-bang nucleosynthesis (IBBN) model. In this letter, we propose that the fluctuations amplified by the vanishing sound velocity effect may produce nonlinear QGP lumps which will survive till today in the form of QNs.…”