Magnetic Fields from QCD Phase Transitions
  We study the evolution of QCD phase transition-generated magnetic fields in
freely decaying MHD turbulence of the expanding Universe. We consider a
magnetic field generation model that starts from basic non-perturbative QCD
theory and predicts stochastic magnetic fields with an amplitude of the order
of 0.02 $\mu$G and small magnetic helicity. We employ direct numerical
simulations to model the MHD turbulence decay and identify two different
regimes: "weakly helical" turbulence regime, when magnetic helicity increases
during decay, and "fully helical" turbulence, when maximal magnetic helicity is
reached and an inverse cascade develops. The results of our analysis show that
in the most optimistic scenario the magnetic correlation length in the comoving
frame can reach 10 kpc with the amplitude of the effective magnetic field being
0.007 nG. We demonstrate that the considered model of magneto-genesis can
provide the seed magnetic field for galaxies and clusters.
