Bethe-Salpeter Amplitudes and Static Properties of the Deuteron

Extended calculations of the deuteron's static properties, based on the numerical solution of the Bethe-Salpeter equation, are presented. A formalism is developed, which provides a comparative analysis of the covariant amplitudes in various representations and nonrelativistic wave functions. The magnetic and quadrupole moments of the deuteron are calculated in the Bethe-Salpeter formalism and the role of relativistic corrections is discussed.Comment: 33 pages ([aps]{revtex} style), 9 Postscript figures; (55 pages if [preprint,aps]{revtex} style is used

Neutral #rho# meson properties in an isospin-asymmetric pion medium

We evaluate the #rho# meson self energy at finite temperature T and charged-pion chemical potential #mu#_Q as well by utilizing a conventional #pi#-#rho# effective Lagrangian and functional integral representation of the partition function in the one-pion loop order (i.e., second order in the #rho##pi##pi# coupling constant). We find an increase of both the #rho# meson mass and the width with increasing temperature and chemical potential #mu#_Q. At large value of #mu#_Q this increases may be about two times larger as compared with the pure temperature shift of Gale and Kapusta at vanishing #mu#_Q. (orig.)Available from TIB Hannover: RR 1847(94-66) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Kaon polarization in nuclear matter

The kaon-nucleon interaction in nuclear matter is considered by taking into account tree graphs, p-wave interaction, pionic intermediate states, kaon fluctuations and some residual interaction. The latter one is constrained by Adler's consistency condition. The K"-, K"+, K"0, anti K"0 polarization operators are calculated in cold nuclear matter with arbitrary isotopic composition. An extra s-wave repulsion is found, which probably shifts the critical point of a K"- condensation with vanishing kaon momentum to large nucleon densities. Oppositely, an extra p-wave attraction is obtained, which may lead to a K"- condensation at vanishing temperatures and densities #rho##>=##rho#_c"-#approx#(4-6)#rho#_0. The spectrum of the kaonic excitations in nuclear matter is analyzed and a new low-lying branch in the K"- (and also anti K"0) spectrum is found. Its presence may lead to interesting observable consequences, such as the enhancement of the K"- yields in heavy-ion reactions. At #rho##>=##rho#_c"- the frequency of this low-lying branch becomes negative at non-vanishing momentum; that signals the onset of inhomogeneous K"-condensation. The K"- condensate energy is calculated in the approximation of a small KK coupling constant. Accordingly, neutron matter may undergo a first-order phase transition to proton matter with K"- condensate at #rho#>#rho#_c"-. The temperature dependence of the most important terms of the K"- polarization operator is discussed. In a rather wide temperature region 0<T<m_#pi#/2 a growing temperature enlarges the K"-N attraction and promotes the kaon condensation. The possibility of anti K"0 condensation is also considered. The question is qualitatively discussed whether proton matter with K"-condensate or neutron matter with anti K"0 condensate is energetically more favorable. (orig.)Available from TIB Hannover: RR 1847(94-40) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Quasi-particle description of a strongly interacting pion gas

The pion self-energy and propagator in a pion gas at temperature T #approx# m_#pi# are calculated within Hartree approximation. The pion-pion interaction is described by Weinberg's Lagrangian. The modification of the pion spectrum consists in the replacement of the free pion mass by an effective one which increases with growing temperature. The thermodynamical quantities can be described by a quasi-particle representation and turn out to be smaller than in a free pion gas. (orig.)Available from TIB Hannover: RR 1847(93-28) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Photon production in an expanding and chemically equilibrating gluon-enriched plasma

Photon production in a longitudinally and transversely expanding gluon plasma with initially little quark admixture is considered. Chemical equilibration of quarks and gluons is followed by rate equations. The yields of hard photons with E #>=# 2 GeV are insensitive to chemical equilibration and depend mainly on the initial thermalized state. Medium-energy photons with E #approx# 1 GeV are more frequently produced in case of faster equilibration, despite of faster cooling. For an assumed fast equilibration we follow the evolution of matter through mixed and hadron phases. The transverse momentum kick, due to transverse expansion, of photons from hadron matter is shown to be reduced for an equation of state with reduced latent heat. The photon yield in the region E > 1 GeV from deconfined matter dominates for conditions, estimated to be achieved at RHIC, in case of a weakly first-order confinement transition. (orig.)Available from TIB Hannover: RR 1847(93-29) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Transverse momentum dependence of dileptons from parton matter produced in ultrarelativistic heavy-ion collisions

The M _p_e_r_p_e_n_d_i_c_u_l_a_r _t_o scaling property of the dilepton spectrum from early parton matter in ultrarelativistic heavy collisions is analyzed for various mechanisms of initial parton production. If there is no essentially additional scale in the parton distribution we find even for strong off-equilibrium parton matter appproximate scaling, while such scales as low-momentum cut-off or parton mass cause strong scaling violations. (orig.)Available from TIB Hannover: RR 1847(93-23) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Kinetics of an expanding pion gas and low-mass dilepton emission

We study the space-time dependence of muon pair production from dense, non-equilibrium pion matter in the framework of a Boltzmann type transport model which properly includes effects of Bose statistics. Starting from an initially supersaturated pion gas with a large positive effective chemical potential we find that this pion chemical potential stays approximately constant during the evolution. As a consequence such a scenario leads to an increased dilepton yield near the kinematical threshold for muon pair production via pion annihilation. Depending on the lifetime of the dense hadron matter formed in relativistic heavy ion collisions, this component can e observed above the background of muon pair from resonance decays and the #rho#,#omega# bump. In such a way the measurement of the di-muon invariant mass spectrum could help to understand the initial state and the dynamical evolution of ultrarelativistic heavy ion collisions. (orig.)SIGLEAvailable from TIB Hannover: RR 1847(93-07) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The role of the massive photon decay channel for the neutrino cooling of neutron stars

The role of the massive photon decay via intermediate states of electron-electron-holes and proton-proton-holes into neutrino-anti-neutrino pairs in the course of neutron star cooling is investigated. These reactions may be operative in hot neutron stars in the region of proton pairing. The corresponding contribution to the neutrino emissivity is calculated. It varies with the temperature as T"3"/2e-m_#gamma#T/ for T<m_#gamma#, where m_#gamma# is an effective photon mass in superconducting matter. Estimates show that this process appears as strong cooling channel of neutron stars at temperatures T#approx =#(10"9-10"1"0) K. (orig.)14 refs.Available from TIB Hannover: RR 1847(95-117) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Electromagnetic signals from deconfined matter resulting from ultrarelativistic heavy-ion collisions

Electromagnetic radiation off strongly interacting matter resulting from ultrarelativistic heavy-ion collisions is estimated. We consider virtual photons (dileptons) and real photons produced in the course of cooling thermalized matter. The chemical evolution of initially undersaturated parton matter coupled to the longitudinal and transverse expansion is followed. Due to the strong transverse expansion the socalled M _p_e_r_p_e_n_d_i_c_u_l_a_r _t_o scaling is restored. Some estimates of contributions of the pre-equilibrium stage are presented. (orig.)SIGLEAvailable from TIB Hannover: RR 1847(136) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany)DEGerman

The impact of kaon polarization in nuclear matter on the K"- production in heavy-in collisions

The impact of the kaon polarization in nuclear matter on the K"- yield in intermediate-energy heavy-ion collisions is investigated. Our scenario of the strange particle production and dynamics is based on an expanding fireball model. This allows for a proper account of in-medium effects. A relation between observed K"+ and K"- yields is derived. Differential K"- cross sections are calculated and compared with available experimental data taken at various collision energies. It turns out that in-medium effects can modify the K"-yields by factors 2 to 5 at beam energies between 2 and 1 AGeV. (orig.)33 refs.Available from TIB Hannover: RR 1847(95-91) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman