arXiv subjects

O. Scavenius

Publications and source records attributed to O. Scavenius.

9 recordsLinked to original sources

arXiv2002

The K/pi ratio from condensed Polyakov loops

We perform a field-theoretical computation of hadron production in large systems at the QCD confinement phase transition associated with restoration of the Z(3) global symmetry. This occurs from the decay of a condensate for the Polyakov loop. From the effective potential for the Polyakov loop, its mass just below the confinement temperature T_c is in between the vacuum masses of the pion and that of the kaon. Therefore, due to phase-space restrictions the number of produced kaons is roughly an order of magnitude smaller than that of produced pions, in agreement with recent results from collisions of gold ions at the BNL-RHIC. From its mass, we estimate that the Polyakov loop condensate is characterized by a (spatial) correlation scale of 1/m_\ell ~ 1/2 fm. For systems of deconfined matter of about that size, the free energy may not be dominated by a condensate for the Polyakov loop, and so the process of hadronization may be qualitatively different as compared to large systems. In that vein, experimental data on hadron abundance ratios, for example K/pi, in high-multiplicity pp events at high energies should be very interesting.

hep-ph↗

arXiv2001

Explosive Decomposition in Ultrarelativistic Heavy Ion Collision

Recent results from Au+Au collisions at BNL-RHIC energy hint at explosive hadron production at the QCD transition rather than soft hydrodynamic evolution. We speculate that this is due to a rapid variation of the effective potential for QCD close to Tc. Performing real-time lattice simulations of an effective theory we show that the fast evolution of the potential leads to ``explosive'' spinodal decomposition rather than bubble nucleation or critical slowing down.

hep-ph↗

arXiv2001

First-Order Chiral Phase Transition in High-Energy Collisions: Can Nucleation Prevent Spinodal Decomposition?

We discuss homogeneous nucleation in a first-order chiral phase transition within an effective field theory approach to low-energy QCD. Exact decay rates and bubble profiles are obtained numerically and compared to analytic results obtained with the thin-wall approximation. The thin-wall approximation overestimates the nucleation rate for any degree of supercooling. The time scale for critical thermal fluctuations is calculated and compared to typical expansion times for high-energy hadronic or heavy-ion collisions. We find that significant supercooling is possible, and the relevant mechanism for phase conversion might be that of spinodal decomposition. Some potential experimental signatures of supercooling, such as an increase in the correlation length of the scalar condensate, are also discussed.

hep-ph↗

arXiv2000

Hydrodynamic Models for Heavy-Ion Collisions, and beyond

A generic property of a first-order phase transition in equilibrium, and in the limit of large entropy per unit of conserved charge, is the smallness of the isentropic speed of sound in the ``mixed phase''. A specific prediction is that this should lead to a non-isotropic momentum distribution of nucleons in the reaction plane (for energies around 40 AGeV in our model calculation). On the other hand, we show that from present effective theories for low-energy QCD one does not expect the thermal transition rate between various states of the effective potential to be much larger than the expansion rate, questioning the applicability of the idealized Maxwell/Gibbs construction. Experimental data could soon provide essential information on the dynamics of the phase transition.

nucl-th↗

arXiv2000

Chiral Phase Transition within Effective Models with Constituent Quarks

We investigate the chiral phase transition at nonzero temperature $T$ and baryon-chemical potential $μ_B$ within the framework of the linear sigma model and the Nambu-Jona-Lasinio model. For small bare quark masses we find in both models a smooth crossover transition for nonzero $T$ and $μ_B=0$ and a first order transition for T=0 and nonzero $μ_B$. We calculate explicitly the first order phase transition line and spinodal lines in the $(T,μ_B)$ plane. As expected they all end in a critical point. We find that, in the linear sigma model, the sigma mass goes to zero at the critical point. This is in contrast to the NJL model, where the sigma mass, as defined in the random phase approximation, does not vanish. We also compute the adiabatic lines in the $(T,μ_B)$ plane. Within the models studied here, the critical point does not serve as a ``focusing'' point in the adiabatic expansion.

nucl-th↗

arXiv2000

An Effective Model for Hot Gluodynamics

We consider an effective Lagrangian containing contributions from glueball and gluon degrees of freedom with a scale-invariant coupling between the two. The thermodynamic potential is calculated taking into account thermal fluctuations of both fields. The glueball mean field dominates at low temperature, while the high temperature phase is governed by low-mass gluon-like excitations. The model shows some similarities to the lattice results in the pure glue sector of QCD. In particular, it exhibits a strong first order phase transition at a critical temperature of approximately 265 MeV when reasonable parameters are taken.

nucl-th↗

arXiv1999

First-order chiral phase transition may naturally lead to the ``quenched'' initial condition and strong soft-pion fields

We propose a novel mechanism for DCC formation in a first-order chiral phase transition. In this case the effective potential for the chiral order parameter has a local minimum at $Φ\sim 0$ in which the chiral field can be ``trapped''. If the expansion is sufficiently fast a bubble of disoriented chiral field can emerge and decouple from the rest of the fireball. The bubble may overshoot the mixed phase and subsequently supercool until the barrier disappears, when the potential resembles that at T=0. This situation corresponds to the initial condition realized in a ``quench''. Thus, the subsequent alignment in the vacuum direction leads to strong amplification of low momentum modes of the pion field. We propose that these DCCs could accompany the previously suggested baryon rapidity fluctuations.

hep-ph↗

arXiv1998

Fluid Dynamical Description of the Chiral Transition

We investigate the dynamics of the chiral transition in an expanding quark-anti-quark plasma. The calculations are made within a linear sigma model with explicit quark and antiquark degrees of freedom. We solve numerically the classical equations of motion for chiral fields coupled to the fluid dynamical equations for the plasma. Fast initial growth and strong oscillations of the chiral field and strong amplification of long wavelength modes of the pion field are observed in the course of the chiral transition.

hep-ph↗

arXiv1997

Dynamical generation of the constituent mass in expanding plasma

We investigate dynamics of the chiral transition in expanding quark-antiquark plasma produced in an ultra-relativistic heavy ion collision. The chiral symmetry break-down and dynamical generation of the constituent quark mass are studied within the linear sigma model and Nambu-Jona-Lasinio model. Time dependence of the quark and antiquark densities is obtained from the scaling solution of the relativistic Vlasov equation. Fast initial growth and strong oscillations of the constituent quark mass are found in the linear sigma model as well as in the NJL model, when derivative terms are taken into account.

hep-ph↗