Dynamical screening in hot systems away from (chemical) equilibrium

Within the Closed Time Path Formalism of Thermal Field Theory we calculate the hard photon emission rate as well as the collisional energy-loss rate for a quark-gluon plasma away from chemical equilibrium. Mass singularities are shown to be dynamically screened within HTL-resummed perturbation theory also away from equilibrium. Additional (pinch) singularities are absent and well defined results are obtained.Comment: Talk given at the Japanese Workshop on Thermal Quantum Field Theories and their Applications, Kyoto, Japan, 25.-27. August 1999, 6 page

Dynamical screening away from equilibrium: hard photon production and collisional energy loss

We investigate the production rate for hard real photons and the collisional energy loss in the quark-gluon plasma away from chemical equilibrium. Applying the Hard-Thermal-Loop resummation scheme away from equilibrium, we can show that Landau damping provides dynamical screening for both fermion and boson exchange present in the two quantities.Comment: 5 pages RevTeX, 2 figures, remarks for clarification and one reference added, typos correcte

Probability distributions in statistical ensembles with conserved charges

The probability distributions for charged particle numbers and their densities are derived in statistical ensembles with conservation laws. It is shown that if this limit is properly taken then the canonical and grand canonical ensembles are equivalent. This equivalence is proven on the most general, probability distribution level.Comment: 5 pages. A little bit shorter version due to some editorial and language changes. To be published in Phys. Rev.

The canonical effect in statistical models for relativistic heavy ion collisions

Enforcing exact conservation laws instead of average ones in statistical thermal models for relativistic heavy ion reactions gives raise to so called canonical effect, which can be used to explain some enhancement effects when going from elementary (e.g. pp) or small (pA) systems towards large AA systems. We review the recently developed method for computation of canonical statistical thermodynamics, and give an insight when this is needed in analysis of experimental data.Comment: 4 pages, 3 figures. Talk given in Strangeness in Quark Matter, Frankfurt am Main 2001. Submitted to J. Phys. G: Nucl. Part. Phy

Thermodynamic limit and semi--intensive quantities

The properties of statistical ensembles with abelian charges close to the thermodynamic limit are discussed. The finite volume corrections to the probability distributions and particle density moments are calculated. Results are obtained for statistical ensembles with both exact and average charge conservation. A new class of variables (semi--intensive variables) which differ in the thermodynamic limit depending on how charge conservation is implemented in the system is introduced. The thermodynamic limit behavior of these variables is calculated through the next to leading order finite volume corrections to the corresponding probability density distributions.Comment: 11 pages, 2 figures In v2 figures are added and corresponding editorial changes are done. Paper will be published in Journal of Physics

Path integral evaluation of equilibrium isotope effects

A general and rigorous methodology to compute the quantum equilibrium isotope effect is described. Unlike standard approaches, ours does not assume separability of rotational and vibrational motions and does not make the harmonic approximation for vibrations or rigid rotor approximation for the rotations. In particular, zero point energy and anharmonicity effects are described correctly quantum mechanically. The approach is based on the thermodynamic integration with respect to the mass of isotopes and on the Feynman path integral representation of the partition function. An efficient estimator for the derivative of free energy is used whose statistical error is independent of the number of imaginary time slices in the path integral, speeding up calculations by a factor of 60 at 500 K. We describe the implementation of the methodology in the molecular dynamics package Amber 10. The method is tested on three [1,5] sigmatropic hydrogen shift reactions. Because of the computational expense, we use ab initio potentials to evaluate the equilibrium isotope effects within the harmonic approximation, and then the path integral method together with semiempirical potentials to evaluate the anharmonicity corrections. Our calculations show that the anharmonicity effects amount up to 30% of the symmetry reduced reaction free energy. The numerical results are compared with recent experiments of Doering and coworkers, confirming the accuracy of the most recent measurement on 2,4,6,7,9-pentamethyl-5-(5,5-$^2$H$_2$)methylene-11,11a-dihydro-12H-naphthacene as well as concerns about compromised accuracy, due to side reactions, of another measurement on 2-methyl-10-(10,10-$^2$H$_2$)methylenebicyclo[4.4.0]dec-1-ene.Comment: 14 pages, 8 figures, 6 table

Antimatter production in proton-proton and heavy-ion collisions at ultrarelativistic energies

One of the striking features of particle production at high beam energies is the near equal abundance of matter and antimatter in the central rapidity region. In this paper we study how this symmetry is reached as the beam energy is increased. In particular, we quantify explicitly the energy dependence of the approach to matter/antimatter symmetry in proton-proton and in heavy-ion collisions. Expectations are presented also for the production of more complex forms of antimatter like antihypernuclei.Comment: 7 pages, 5 figure

Photon and Dilepton Production from Hot Out-Off-Equilibrium Media

The electromagnetic emissivity from QCD media away from equilibrium is studied in the framework of closed time path thermal field theory. For the dilepton rate a nonequilibrium mesonic medium is considered applying finite temperature perturbation theory for $\pi -\rho$ interactions. The dilepton rate is derived up to the order $g_\rho^2$. For hard photon production a quark gluon plasma is assumed and calculations are performed in leading order in the strong coupling constant. These examples are chosen in order to investigate the role of possible pinch terms in boson and in fermion propagators, respectively. The implications of the results for phenomenology are also discussed.Comment: 16 pages LaTeX, 11 figures using epsfig. To be published in the proceedings of the XXXVII-th Cracow School of Theoretical Physics, Dynamics of Strong Interactions, Zakopane, June 199