Equation of state for β\beta-stable hot nuclear matter

We provide an equation of state for hot nuclear matter in $\beta$-equilibrium by applying a momentum-dependent effective interaction. We focus on the study of the equation of state of high-density and high-temperature nuclear matter, containing leptons (electrons and muons) under the chemical equilibrium condition in which neutrinos have left the system. The conditions of charge neutrality and equilibrium under $\beta$-decay process lead first to the evaluation of proton and lepton fractions and afterwards of internal energy, free energy, pressure and in total to the equation of state of hot nuclear matter. Thermal effects on the properties and equation of state of nuclear matter are assesed and analyzed in the framework of the proposed effective interaction model. Special attention is dedicated to the study of the contribution of the components of $\beta$-stable nuclear matter to the entropy per particle, a quantity of great interest for the study of structure and collapse of supernova.Comment: 28 pages, 18 figure

Temperature and momentum dependence of single-particle properties in hot asymmetric nuclear matter

We have studied the effects of momentum dependent interactions on the single-particle properties of hot asymmetric nuclear matter. In particular, the single-particle potential of protons and neutrons as well as the symmetry potential have been studied within a self-consistent model using a momentum dependent effective interaction. In addition, the isospin splitting of the effective mass has been derived from the above model. In each case temperature effects have been included and analyzed. The role of the specific parametrization of the effective interaction used in the present work has been investigated. It has been concluded that the behavior of the symmetry potential depends strongly on the parametrization of the interaction part of the energy density and the momentum dependence of the regulator function. The effects of the parametrization have been found to be less pronounced on the isospin mass splitting.Comment: 22 pages, 14 figure

Equation of state for dense supernova matter

We provide an equation of state for high density supernova matter by applying a momentum-dependent effective interaction. We focus on the study of the equation of state of high-density and high-temperature nuclear matter containing leptons (electrons and neutrinos) under the chemical equilibrium condition. The conditions of charge neutrality and equilibrium under $\beta$-decay process lead first to the evaluation of the lepton fractions and afterwards the evaluation of internal energy, pressure, entropy and in total to the equation of state of hot nuclear matter for various isothermal cases. Thermal effects on the properties and equation of state of nuclear matter are evaluated and analyzed in the framework of the proposed effective interaction model. Since supernova matter is characterized by a constant entropy we also present the thermodynamic properties for isentropic case. Special attention is dedicated to the study of the contribution of the components of $\beta$-stable nuclear matter to the entropy per particle, a quantity of great interest for the study of structure and collapse of supernova.Comment: 23 pages, 15 figure

Lifetime Measurements in 120Xe

Lifetimes for the lowest three transitions in the nucleus $^{120}$Xe have been measured using the Recoil Distance Technique. Our data indicate that the lifetime for the $2_{1}^{+} \to 0_{1}^{+}$ transition is more than a factor of two lower than the previously adopted value and is in keeping with more recent measurements performed on this nucleus. The theoretical implications of this discrepancy and the possible reason for the erroneous earlier results are discussed. All measured lifetimes in $^{120}$Xe, as well as the systematics of the lifetimes of the 2$_{1}^{+}$ states in Xe isotopes, are compared with predictions of various models. The available data are best described by the Fermion Dynamic Symmetry Model (FDSM).Comment: 9 pages, RevTeX, 3 figures with Postscript file available on request at [email protected], [email protected]. Submitted to Phys. Rev.

Shifting the quantum Hall plateau level in a double layer electron system

We study the plateaux of the integer quantum Hall resistance in a bilayer electron system in tilted magnetic fields. In a narrow range of tilt angles and at certain magnetic fields, the plateau level deviates appreciably from the quantized value with no dissipative transport emerging. A qualitative account of the effect is given in terms of decoupling of the edge states corresponding to different electron layers/Landau levels.Comment: 3 pages, 3 figures include

A new window on Strange Quark Matter as the ground state of strongly interacting matter

If strange quark matter is the true ground state of matter, it must have lower energy than nuclear matter. Simultaneously, two-flavour quark matter must have higher energy than nuclear matter, for otherwise the latter would convert to the former. We show, using an effective chiral lagrangian, that the existence of a new lower energy ground state for two-flavour quark matter, the pion condensate, shrinks the window for strange quark matter to be the ground state of matter and sets new limits on the current strange quark mass

A fully relativistic radial fall

Radial fall has historically played a momentous role. It is one of the most classical problems, the solutions of which represent the level of understanding of gravitation in a given epoch. A {\it gedankenexperiment} in a modern frame is given by a small body, like a compact star or a solar mass black hole, captured by a supermassive black hole. The mass of the small body itself and the emission of gravitational radiation cause the departure from the geodesic path due to the back-action, that is the self-force. For radial fall, as any other non-adiabatic motion, the instantaneous identity of the radiated energy and the loss of orbital energy cannot be imposed and provide the perturbed trajectory. In the first part of this letter, we present the effects due to the self-force computed on the geodesic trajectory in the background field. Compared to the latter trajectory, in the Regge-Wheeler, harmonic and all others smoothly related gauges, a far observer concludes that the self-force pushes inward (not outward) the falling body, with a strength proportional to the mass of the small body for a given large mass; further, the same observer notes an higher value of the maximal coordinate velocity, this value being reached earlier on during infall. In the second part of this letter, we implement a self-consistent approach for which the trajectory is iteratively corrected by the self-force, this time computed on osculating geodesics. Finally, we compare the motion driven by the self-force without and with self-consistent orbital evolution. Subtle differences are noticeable, even if self-force effects have hardly the time to accumulate in such a short orbit.Comment: To appear in Int. J. Geom. Meth. Mod. Phy

Stellar and thermal neutron capture cross section of ⁹Be

The neutron capture cross section of ⁹Be for stellar energies was measured via the activation technique using the Karlsruhe Van de Graaff accelerator in combination with accelerator mass spectrometry at the Vienna Environmental Research Accelerator. To characterize the energy region of interest for astrophysical applications, activations were performed in a quasistellar neutron spectrum of kT = 25 keV and for a spectrum at En = 473 ± 53 keV. Despite the very small cross section, the method used provided the required sensitivity for obtaining fairly accurate results of 10.4 ± 0.6 and 8.4 ± 1.0 μb, respectively. With these data it was possible to constrain the cross section shape up to the first resonances at 622 and 812 keV, thus allowing for the determination of Maxwellian-averaged cross sections at thermal energies between kT = 5 and 100 keV. In addition, we report a new experimental cross section value at thermal energy of σth = 8.31 ± 0.52 mb.This work was partly funded by the Austrian Science Fund (FWF), Projects No. P20434 and No. I428, and by the Australian Research Council, Projects No. DP140100136 and No. DP180100496

Quark Hadron Phase Transition and Hybrid Stars

We investigate the properties of hybrid stars consisting of quark matter in the core and hadron matter in outer region. The hadronic and quark matter equations of state are calculated by using nonlinear Walecka model and chiral colour dielectric (CCD) model respectively. We find that the phase transition from hadron to quark matter is possible in a narrow range of the parameters of nonlinear Walecka and CCD models. The transition is strong or weak first order depending on the parameters used. The EOS thus obtained, is used to study the properties of hybrid stars. We find that the calculated hybrid star properties are similar to those of pure neutron stars.Comment: 25 pages in LaTex and 9 figures available on request, IP/BBSR/94-3