Baryon-number fluctuations in a quark-hadron phase transition

Abstract

Isothermal baryon-number fluctuations arising from a first-order quark-hadron phase transition in the early Universe are obtained by including the quark-gluon interactions up to the order gj in the perturbative QCD coupling constant in the quark-gluon plasma (QGP) phase and the finite-size volume corrections for the hadrons in the hadron-resonance gas (HRG) and their effects on the primordial nucleosynthesis (PNS) are analyzed. The ratio of the baryon-number densities in the QGP and HRG phases at the critical temperature T, is larger than one in the range 150 MeV < T, < 260 MeV. However, it is far larger than one even when T, is outside this range, thus affecting primordial nucleosynthesis significantly.PACS number(s1: 04.40. Dg, 12.38.Mh, 98.80.Ft The nature and the critical parameters of the phase transition between a hadron resonance gas (HRG) and the quark-gluon plasma (QGP) are the object of active theoretical and experimental research [1,2]. At very high temperatures in the early Universe, we believe that the colored quarks and gluons were unconfined and the matter existed in the form of a QGP. As the Universe expanded, the temperature dropped through the critical temperature Tc for the phase transition where the Q G P could exist in thermal, mechanical, and chemical equilibrium with a dense hot gas of H R G . Isothermal baryonnumber fluctuation is a natural consequence of a firstorder phase transition between a Q G P and HRG. Consequently, a large local fluctuation in the baryon-to-photon ratio results and thus alters the predictions of the standard scenario for primordial nucleosynthesis (PNS). The ratio of baryon-number densities in the two phases is represented by and the expression is evaluated at T = T c and baryon chemical potential p, <<Tc. When R >> 1, the baryon number of the Universe preferentially remained in the Q G P phase during the period of phase separation and thus affected the PNS significantly.Several authors have calculated [3-81 the value of R by assuming a Q G P as an ideal thermodynamical gas of quarks and gluons and the H R G was treated as an ideal gas of protons and neutrons. Turner [ 3 ] noticed that the ratio R decreases significantly when other low-lying baryon states, e.g., A (mass 1232 MeV, ~' = 3 / 2 ' and I = 3 / 2 ) , A, 2', zO, and 2 -(strangeness = -1 states) were included. H e found that unless Tc < 150 MeV, the effects of the phase transition upon PNS would not be significant. However, they found R << 1 for Tc > 250 MeV and that the baryon number resides predominantly in the H R G phase. Recently, Murugesan et al. [ 4 ] used relativistic quantum statistics for particles in both the phases and Hagedorn's correction for the finite size of the hadrons in the H R G phase. They found that these corrections lower the value of Tc and, unless Tc 5 125MeV and R > 10, the phase transition would not have any significant effect upon PNS. The purpose of this paper is to explore the results when a phase transition from a Q G P with interacting quarks and gluons to a hadron gas co...

Hadronic interactions and the deconfinement phase transition

“…Another source of uncertainty in the QGP phase apart from the bag parameter B is the QCD scale parameter . The present calculations have been performed by using the value = 100 MeV [12,16], but a value twice as large is perhaps nearer to what one expects for a standard QCD scale parameter. Since we use a running coupling constant depending on T , µ B and , a variation in may significantly change the results of QGP pressure, and consequently the phase transition.…”

“…However, there still remain uncertainties in the equation of state (EOS) in both the deconfined and the confined phases. Studies have shown [12] that QCD interactions up to g 3 in the coupling constant are important in the QGP phase, so much so that they not only negate the g 2 contributions, but drive the phase curves away from that of the the zeroth order by an equal amount in the opposite direction.…”

Viscous effects on the dynamical evolution of QCD matter during the first-order confinement phase transition in heavy-ion collisions

“…(5) Here we neglect the logarithmic dependence of α s on µ q . The hadron phase is described by the hadron resonance gas model (HRG) [15][16][17]. Baryons, mesons, and their resonances having masses up to 2 GeV are included.…”

Baryon number penetrability as a measure of isothermal baryon number fluctuations in the early universe

“…The baryon number density inhomogeneity arising due to such a quark-hadron phase transition will thus alter the yields of the PNS which is a function of R eq and the neutron to proton (n/p) ratio [10]. Several theoretical attempts have been recently made to determine the values of R eq [11][12][13][14].…”