Stanislaw Mrowczynski

Plasma instability at the initial stage of ultrarelativistic heavy-ion collisions☆

Abstract Hard and semihard processes lead to a copious production of partons at the initial stage of ultrarelativistic heavy-ion collisions. Since the parton momentum distribution is strongly anisotropic the system can be unstable with respect to the specific plasma modes. The conditions of instability are found and the characteristic time of its development is estimated. Relevance of the phenomenon for heavy-ion collisions at RHIC and LHC is briefly discussed.

A method to study “equilibration” in nucleus-nucleus collisions

A method to study “equilibration level” of a system created in high energy nucleus-nucleus collisions is proposed. The method is based on the fact that the correlation between momentum distribution and particle multiplicity observed in nucleon-nucleon interactions can be also measured in nucleus-nucleus collisions. It is argued that the magnitude of the residual correlation can be used as a measure of the system “equilibration level”. The method is effective even when changes of the “equilibration level” do not modify the inclusive distribution. The quantitative estimate of the effect to be measured is given. Finally, questions arising in practical application of the method are discussed.

Hard-loop effective action for anisotropic plasmas

We generalize the hard-thermal-loop effective action of the equilibrium quark-gluon plasma to a nonequilibrium system which is space-time homogeneous but for which the parton momentum distribution is anisotropic. We show that the manifestly gauge-invariant Braaten-Pisarski form of the effective action can be straightforwardly generalized and we verify that it then generates all n-point functions following from collisionless gauge-covariant transport theory for a homogeneous anisotropic plasma. On the other hand, the Taylor-Wong form of the hard-thermal-loop effective action has a more complicated generalization to the anisotropic case. Already in the simplest case of anisotropic distribution functions, it involves an additional term that is gauge invariant by itself, but nontrivial also in the static limit.

Energy loss of a high-energy parton in the quark-gluon plasma

Abstract The energy loss of a high-energy parton (quark or gluon) traversing the equilibrium quark-gluon plasma is discussed. The collisions with the thermalized plasma partons and the plasma polarization effects are considered in detail. The calculations and the final results are confronted with those of previous papers.

Green function approach to transport theory of scalar fields

Abstract The contour Green function technique is used to derive the relativistic transport equations of neutral and charged scalar fields with the interaction lagrangian densities proportional to φ3 and (φφ ∗ 2 , respectively. The mean field and the collision terms in the equations are discussed in detail.

Chromohydrodynamic approach to the unstable quark-gluon plasma

We derive hydrodynamic-like equations that are applicable to short-time-scale color phenomena in the quark-gluon plasma. The equations are solved in the linear response approximation, and the gluon polarization tensor is derived. As an application, we study the collective modes in a two-stream system and find plasma instabilities when the fluid velocity is larger than the speed of sound in the plasma. The chromohydrodynamic approach, discussed here in detail, should be considered as simpler over other approaches and well-designed for numerical studies of the dynamics of an unstable quark-gluon plasma.

Reheating after supercooling in the chiral phase transition

Abstract We study the conversion of the latent heat of a supercooled quark-gluon plasma into excitations of the pion field. Supercooling is predicted to occur in the late stages of the evolution of a quark-gluon plasma produced in energetic heavy-ion collisions, if the QCD phase transition is of first order. The supercooled, chirally symmetric state, which contains potential energy associated with an energetically unfavorable field configuration, eventually rolls down to the true minimum of the effective chiral potential. When this motion is described in terms of the linear sigma-model, we find that the energy of the coherent σ-field is very efficiently converted into pionic excitations due to anharmonic oscillations around the minimum. The system is expected to partially thermalize before its disintegration.

Color instabilities in the quark–gluon plasma

When the quark-gluon plasma (QGP) - a system of deconfined quarks and gluons - is in a nonequilibrium state, it is usually unstable with respect to color collective modes. The instabilities, which are expected to strongly influence dynamics of the QGP produced in relativistic heavy-ion collisions, are extensively discussed under the assumption that the plasma is weakly coupled. We begin by presenting the theoretical approaches to study the QGP, which include: field theory methods based on the Keldysh-Schwinger formalism, classical and kinetic theories, and fluid techniques. The dispersion equations, which give the spectrum of plasma collective excitations, are analyzed in detail. Particular attention is paid to a momentum distribution of plasma constituents which is obtained by deforming an isotropic momentum distribution. Mechanisms of chromoelectric and chromomagnetic instabilities are explained in terms of elementary physics. The Nyquist analysis, which allows one to determine the number of solutions of a dispersion equation without explicitly solving it, and stability criteria are also discussed. We then review various numerical approaches - purely classical or quantum - to simulate the temporal evolution of an unstable quark-gluon plasma. The dynamical role of instabilities in the processes of plasma equilibration is analyzed.

On the neutron—proton correlations and deuteron production

Abstract The neutron-proton correlations and deuteron formation in nuclear collisions both appear due to the final state interactions. Thus, we suggest simulataneous measurements of the neutron—proton correlation function and the deuteron formation rate. We calculate in parallel the two quantities and express them through the space-time parameters of the particle source created in nucleus-nucleus collisions.

Momentum broadening of a fast parton in a perturbative quark-gluon plasma

The average transverse momentum transfer per unit path length to a fast parton scattering elastically in a perturbative quark-gluon plasma is related to the radiative energy loss of the parton. We first calculate the momentum transfer coefficient