Bubble collisions in the cosmological quark-hadron phase transition

Assuming that a first-order QCD phase transition occured in the very early universe, we investigate the growth and collisions of hadron bubbles in the thin-wall approximation. We also discuss a mechanism of baryon number concentration.     

Effect of pre-existing baryon inhomogeneities on the dynamics of quark-hadron transition

Baryon number inhomogeneities may be generated during the epoch when the baryon asymmetry of the universe is produced, e.g. at the electroweak phase transition. These lumps will have a lower temperature than the background. Also the value ofT _c will be different in these regions. Since a first-order quark-hadron (Q–H) transition is susceptible to small changes in temperature, we investigate the effect of the presence of such baryonic lumps on the dynamics of the Q–H transition. We find that the phase transition is delayed in these lumps for significant overdensities. Consequently, we argue that baryon concentration in these regions grows by the end of the transition. We mention some models which may give rise to such high baryon overdensities before the Q–H transition.     

Axion oscillations and the quark-hadron phase transition

We consider the possibility that the quark-hadron phase transition occurs when the axion field passes through the minimum of its potential during its oscillation cycle. If this were to occur, the axion field would gain no energy from the associated increase in mass thus permitting the cosmological bound on the axion decay constant to be raised. However, we find that the probability of this happening is small.     

Monte Carlo simulations of the short time dynamics of a first-order irreversible phase transition

The ZGB model (Ziff–Gulari–Barshad, Phys. Rev. Lett. 56 (1986) 2553) for the catalytic oxidation of carbon monoxide has a single parameter given by the normalized partial pressure of CO molecules (P_CO). For P_CO⩾P_CO^Coex≃0.52583 the surface of the catalyst becomes irreversibly covered by CO molecules and the system cannot escape from this state. However, for P_CO slightly below P_CO^Coex the system reaches an active stationary state. So, just at P_CO^Coex a sharp first-order irreversible phase transition is observed. It is shown that a study of the short time dynamics of the ZGB model allows to obtain a fairly accurate evaluation of the upper spinodal point given by P_CO^Usp≃0.52675(5). This figure is in excellent agreement with extensive simulations performed using the constant coverage ensemble.     

Growth of clusters in a first-order phase transition

The results of computer simulations of phase separation kinetics in a binary alloy quenched from a high temperature are analyzed in detail, using the ideas of Lifshitz and Slyozov. The alloy was modeled by a three-dimensional Ising model with Kawasaki dynamics. The temperature after quenching was 0.59T _c, whereT _c is the critical temperature, and the concentration of minority atoms was=0.075, which is about five times their largest possible single-phase equilibrium concentration at that temperature. The time interval covered by our analysis goes from about 1000 to 6000 attempted interchanges per site. The size distribution of small clusters of minority atoms is fitted approximately byc ₁(1-)³ w(t),c ₁ (1–)⁴ Q _l w(t)^l(2l10); wherec _l is the concentration of clusters of sizel;Q ₂,...,Q ₁₀ are known constants, the cluster partition functions;t is the time; andw(t)=0.015(1+7.17t ^–1/3). The distribution of large clusters (l20) is fitted approximately by the type of distribution proposed by Lifshitz and Slyozov,c _l ,(t)=–(d/dl) [lnt+p (l/t)], where is a function given by those authors and is defined by(x)=C _o e–x-C ₁ e ^–4x/3-C ₂ e ^–5x/3;C ₀,C ₁,C ₂ are constants determined by considering how the total number of particles in large clusters changes with time.Supported by the U.S. Air Force Office of Scientific Research under Grant No. 78-3522 and by the U.S. Department of Energy under Contract No. EY-76-C-02-3077*000.     

On the nucleation of hadronic domains in the quark-hadron transition

We present numerical results on bubble profiles, nucleation rates and time evolution for a weakly first-order quark-hadron phase transition in different expansion scenarios. We confirm the standard picture of a cosmological first-order phase transition, in which the phase transition is entirely dominated by nucleation. We also show that, even for expansion rates much lower than those expected in heavy-ion collisions nucleation is very unlikely, indicating that the main phase conversion mechanism is spinodal decomposition.     

A first-order crumpling transition

Using a gaussian action with an extrinsic curvature term, we study the finite-size scaling behavior of the crumpling transition of a surface embedded in two dimensions. The data suggest that the transition is first order.