We study how bubbles grow after the initial nucleation event in generic first-order cosmological phase transitions characterized by the values of the latent heat L, interface tension a, and correlation length 6, and driven by a scalar order parameter d. Equations coupling b(t,x) and the fluid variables vit,x), T(t,x) and depending on a dissipative constant l-are derived and solved numerically in the ( 1 + 1)-dimensional case starting from a slightly deformed critical bubble configuration #(O,x). The parameters L, u , & corresponding to QCD and electroweak phase transitions are chosen and the whole history of the bubble with the formation of combustion and shock fronts is computed as a function of I?.Both deflagrations and detonations can appear depending on the values of the parameters. Reheating due to collisions of bubbles is also computed. PACS number(s1: 98.80.Cq,

We study the kinetics of first-order cosmological phase transitions assuming a four-parameter form for the Higgs potential driving the transition. This leads to a phenomenological equation of state for electroweak matter with a stable high-T phase for T > T, and a low-T phase for T < T,. The nucleation probability of low-T bubbles, both critical and subcritical, is computed and their growth and coalescence is simulated. We show that they can grow as deflagrations and that detonations are unlikely. Possible front velocities and entropy production are studied. The results are applied to parameter values conjectured for the electroweak phase transition and compared with those obtained for the quark-hadron phase transition. PACS numberk): 98.80.Cq

We investigate a new mechanism for the cosmological QCD phase transition: inhomogeneous nucleation. The primordial temperature fluctuations, measured to be δT /T ∼ 10 −5 , are larger than the tiny temperature interval, in which bubbles would form in the standard picture of homogeneous nucleation. Thus the bubbles nucleate at cold spots. We find the typical distance between bubble centers to be a few meters. This exceeds the estimates from homogeneous nucleation by two orders of magnitude. The resulting baryon inhomogeneities may affect primordial nucleosynthesis. 98.80.Cq, 12.38.Mh, 64.60.Qb A separation of cosmic phases during a first-order QCD transition [1] could give rise to inhomogeneous nucleosynthesis [2][3][4][5]. During a thermal first-order phase transition in a homogeneous medium bubbles nucleate due to statistical fluctuations (homogeneous nucleation). Their mean separation at nucleation introduces a scale for isothermal inhomogeneities in the early Universe, which may influence the local neutron-to-proton ratio, providing inhomogeneous initial conditions for nucleosynthesis. The baryon inhomogeneities may survive until the time of neutron freeze-out, if the mean bubble nucleation distance, d nuc , exceeds the diffusion length of the proton. Comparing those scales at the time of the QCD transition, assuming a thermodynamic transition temperature T c = 150 MeV, gives d nuc > 2 m [4]. The causal scale is set by the Hubble distance at the QCD transition, d H ≡ c/H ∼ 10 km.The order of the QCD transition and the values of its parameters are still under debate. Nevertheless there are indications from lattice QCD calculations [6][7][8][9][10]. For the physical masses of the quarks the order of the transition is still unclear [6,7]. Quenched QCD (no dynamical quarks) shows a first-order phase transition with a small latent heat, compared to the bag model, and a small surface tension, compared to dimensional arguments [8]. We assume that the QCD transition is of first order and that the values from quenched lattice QCD (scaled appropriately by the number of degrees of freedom) are typical for the physical QCD transition. Based on these values and homogeneous bubble nucleation a small supercooling, ∆ sc ≡ 1−T f /T c ∼ 10 −4 , and a tiny bubble nucleation distance, d nuc ∼ 1 cm, follow [11]. The actual nucleation temperature is denoted by T f .We argue that the assumption of homogeneous nucleation is violated in the early Universe by the inevitable density perturbations from inflation or from other seeds for structure formation. Those fluctuations in density and temperature have been measured by COBE [12] to have an amplitude of δT /T ∼ 10 −5 . The effect of the QCD transition on density perturbations [13,14] and gravitational waves [15] has been studied previously, while we investigate the effect of the density perturbations on the QCD phase transition here. We conclude that a first order QCD transition induces an inhomogeneity scale of a few meters. In comparison with heterogeneous nucleation via ad hoc d...