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

Resonance Model for π\piN Scattering and η\eta-Meson Production in the s11_{11} Channel

A model for $\pi$N scattering and $\eta$-meson production in the S$_{11}$ channel is presented. The model includes $\pi$N-scattering Born terms as well as the N$^*${} resonances S$_{11}$(1535) and S$_{11}$(1610). The $T$-matrix is computed in the $K$-matrix approximation. The parameters of the model are determined by fitting the elastic $\pi$N-scattering $T$-matrix to empirical data. We find an excellent fit for all energies up to $\sqrt{s}$ = 1.75 GeV. Furthermore, a good description of the cross section for $\pi^- + p \rightarrow \eta + n$ is obtained without further adjustment of parameters.Comment: LaTex 10 pages, 4 figures (not included;the postscript-figures are available from [email protected] in subdirectory pub/sauerman, files: fig1.ps, fig2.ps,fig3.ps,fig4.ps- or contact the authors via e-mail), GSI-94-4

Neutron matter at finite temperature

We calculate the neutron matter equation of state at finite temperature based on low-momentum two- and three-nucleon interactions. The free energy is obtained from a loop expansion around the Hartree-Fock energy, including contributions from normal and anomalous diagrams. We focus on densities below saturation density with temperatures T <= 10 MeV and compare our results to the model-independent virial equation of state and to variational calculations. Good agreement with the virial equation of state is found at low density. We provide simple estimates for the theoretical error, important for extrapolations to astrophysical conditions.Comment: 15 pages, 6 figure

Density fluctuations in the presence of spinodal instabilities

Density fluctuations resulting from spinodal decomposition in a non-equilibrium first-order chiral phase transition are explored. We show that such instabilities generate divergent fluctuations of conserved charges along the isothermal spinodal lines appearing in the coexistence region. Thus, divergent density fluctuations could be a signal not only for the critical end point but also for the first order phase transition expected in strongly interacting matter. We also show that the mean-field critical exponent at the spinodal lines and at the critical end point are identical. Our analysis is performed in the mean-field approximation to the NJL model formulated at finite temperature and density. However, our main conclusions are expected to be generic and model independent

Charge Fluctuations along the QCD phase boundary

We discuss the properties of the net--quark and isovector fluctuations along the chiral phase transition line in the plane spanned by temperature and baryon chemical potential. Our results are obtained in terms of the Nambu--Jona-Lasinio (NJL) model within the mean-field approximation. The model is formulated at the finite temperature and for non-vanishing net--quark and the isospin chemical potentials. The fermion interactions are controlled by the strength of the scalar and vector couplings in the iso-scalar and iso-vector channels of constituent quarks. We explore properties and differences in the behavior of the net--quark number and isovector susceptibilities for different values of thermal parameters near the phase transition. We argue that any non-monotonic behavior of the net--quark number susceptibility along the phase transition boundary is an excellent probe of the existence and the position of the second order endpoint in the QCD phase diagram