Meson-nucleon scattering and vector mesons in nuclear matter

The properties of vector mesons in nuclear matter are discussed. I examine the constraints imposed by elementary processes on the widths of $\rho$ and $\omega$ mesons in nuclear matter. Furthermore, results for the $\rho$- and $\omega$-nucleon scattering amplitudes obtained by fitting meson-nucleon scattering data in a coupled-channel approach are presented.Comment: 7 pages, 6 EPS figures, uses appb.sty (included), talk given at Meson98, Cracow, May 98, to be published in Acta Physica Polonica

Three-body interactions in Fermi systems

We show that the contributions of three-quasiparticle interactions to normal Fermi systems at low energies and temperatures are suppressed by n_q/n compared to two-body interactions, where n_q is the density of excited or added quasiparticles and n is the ground-state density. For finite Fermi systems, three-quasiparticle contributions are suppressed by the corresponding ratio of particle numbers N_q/N. This is illustrated for polarons in strongly interacting spin-polarized Fermi gases and for valence neutrons in neutron-rich calcium isotopes.Comment: 16 pages, 1 figure; to appear in Festschrift on the occasion of Gerry Brown's 85th birthday, Ed. Sabine Lee (World Scientific

Kurtosis and compressibility near the chiral phase transition

The properties of net quark number fluctuations in the vicinity of the QCD chiral phase transition are discussed in terms of an effective chiral model in the mean-field approximation. We focus on the ratio of the fourth- to second- order cumulants (kurtosis) and the compressibility of the system and discuss their dependence on the pion mass. It is shown that near the chiral phase transition, both observables are sensitive to the value of $m_\pi$. For physical $m_\pi$, the kurtosis exhibits a peak whereas the inverse compressibility shows a dip at the pseudocritical temperature. These structures disappear for large $m_\pi$. Our results, obtained in an effective model with two flavors, are qualitatively consistent with recent results of 2+1 flavor lattice gauge theory. We also discuss the high- and low-temperature properties of these observables and the role of the coupling of the quark degrees of freedom to the Polyakov loop

Hamiltonian Flow Equations for the Lipkin Model

We derive Hamiltonian flow equations giving the evolution of the Lipkin Hamiltonian to a diagonal form using continuous unitary transformations. To close the system of flow equations, we present two different schemes. First we linearize an operator with three pairs of creation and destruction operators by reducing it to the $z$ component of the quasi spin. We obtain the well known RPA-result in the limit of large particle number. In the second scheme we introduce a new operator which improves the resulting spectrum considerably especially for few particles.Comment: 10 pages, 2 eps figures, uses article.sty, epsfig.st

Susceptibilities and the Phase Structure of a Chiral Model with Polyakov Loops

In an extension of the Nambu-Jona-Lasinio model where the quarks interact with the temporal gluon field, represented by the Polyakov loop, we explore the relation between the deconfinement and chiral phase transitions. The effect of Polyakov loop dynamics on thermodynamic quantities, on the phase structure at finite temperature and baryon density and on various susceptibilities is presented. Particular emphasis is put on the behavior and properties of the fluctuations of the (approximate) order parameters and their dependence on temperature and net--quark number density. We also discuss how the phase structure of the model is influenced by the coupling of the quarks to the Polyakov loop.Comment: 18 pages, 22 figures; text rearranged and references added. results and conclusions unchanged; final version accepted for publication in Phys. Rev.

The neutron matter equation of state from low-momentum interactions

We calculate the neutron matter equation of state at finite temperature based on low-momentum nucleon-nucleon and three-nucleon interactions. Our results are compared to the model-independent virial equation of state and to variational calculations. We provide a simple estimate for the theoretical error, important for extrapolations to astrophysical conditions.Comment: 3 pages, 2 figures, to appear in the proceedings of Quark Confinement and Hadron Spectrum VII (QCHS7), Ponta Delgada (Acores), Portugal, 2-7 September 200

Effective chiral model with Polyakov loops and its application to hot/dense medium

We study the thermodynamics of the Nambu--Jona-Lasinio model with Polyakov loops, where spontaneous chiral symmetry breaking and confinement are taken into account. We focus on the phase structure of the model and explore the susceptibilities associated with corresponding order parameters under the mean-field approximation.Comment: 4 pages, 1 figure, to appear in the proceedings of the Yukawa International Seminars (YKIS) 2006, Nov.27-Dec.1, 2006, Kyoto, Japa

From meson-nucleon scattering to vector mesons in nuclear matter

We employ meson-nucleon scattering data to deduce the properties of the low-mass vector mesons in nuclear matter, and present results for the $\rho$ and $\omega$ in-medium spectral functions. The corresponding thermal emission rate for lepton pairs is also discussed.Comment: Talk given at 28th International Workshop on Gross Properties of Nuclei and Nuclear Excitations, Hirschegg, Austria, 16-22 Jan. 200