Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session X7: Nuclear Astrophysics II |
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Sponsoring Units: DNP Chair: Achim Schwenk, Technical University Darmstadt Room: Grand E |
Tuesday, May 3, 2011 10:45AM - 10:57AM |
X7.00001: Using spin-down of neutron stars as a probe of the phases of ultra-dense matter Simin Mahmoodifar, Mark G. Alford, Kai Schwenzer Spin frequency is the most accurately measurable property of neutron stars. The range of possible frequencies is determined by internal properties, such as the amplitude of ``r-modes,'' which spin the star down by emitting copious gravitational radiation. I will discuss the damping of r-modes by non-linear contributions to the bulk viscosity, which grow with the oscillation amplitude and may become large enough to stop the growth of the r-modes. I will present our results for the viscous damping of the r-modes taking into account the high-amplitude bulk viscosity for different cases of hadronic stars, strange stars and hybrid stars and its effect on the spin-down evolution of the star. [Preview Abstract] |
Tuesday, May 3, 2011 10:57AM - 11:09AM |
X7.00002: A second Equation of State for Astrophysical Simulations Gang Shen, Charles Horowitz, Evan O'Connor In this work, we present a second equation of state (EoS) of nuclear matter for a wide range of temperatures, densities, and proton fractions for use in supernova and neutron star merger simulations. We employ a full relativistic mean field (RMF) calculation for matter at intermediate density and high density, and the Virial expansion of a nonideal gas for matter at low density. The difference from the first EoS is that here we use the RMF parameter set FSUGold whereas the first based on NL3. The FSUGold EoS is considerably softer than NL3 in the high density, but stiffer at subnuclear density. The Virial gas part is common and consists of neutrons, protons, alpha particles, and 8980 species of nuclei with masses from FRDM mass tables. We tabulate the resulting EoS at over 100,000 grid points in the temperature range $T$ = 0 $\sim$ 80 MeV, the density range $n_B$ = 10$^{-8}$ $\sim$ 1.6 fm$^{-3}$, and the proton fraction range $Y_P$ = 0 $\sim$ 0.56. We present the difference between the second EoS and first EoS along with the exisitng EoSs, in the phase diagram, composition, and neutron star structures. This table will soon be available for supernova and neutron star merger simulations. [Preview Abstract] |
Tuesday, May 3, 2011 11:09AM - 11:21AM |
X7.00003: Nonlinear Electromagnetic Force Near Compact Stellar Objects Lance Labun, Johann Rafelski Quantum electrodynamics generates a nonlinear theory of electromagnetism from fluctuations of electron-positron pairs. The nonlinear interactions are suppressed by the field scale $B_c = m_e^2/e = 4.1\times 10^9\:{\rm T}$. Fields approaching this magnitude are thought to be found only in the neighbourhood of strongly-magnetized compact stars, and in these environs the consequences of the nonlinearity are comparable to the effects of gravity. We derive the effective force on a charged particle entering a strong stellar magnetic field. The results show that the nonlinearity of electromagnetism affects the dynamics of plasmas near a compact star even when the stellar magnetic field is well below critical magnitude $B_c$. [Preview Abstract] |
Tuesday, May 3, 2011 11:21AM - 11:33AM |
X7.00004: Multidimensional Simulations of Thermonuclear Supernovae from The First Stars Ke-Jung Chen, Alexander Heger, Ann Almgren Current models of the formation of the first stars in the universe suggest that these stars were very massive, having a typical mass scale of hundreds of solar masses. Such stars would explode as pair instability supernovae (PSNe). These supernovae hold the key to understanding the formation of the first heavy elements and the first galaxy formation in the universe. The current theoretical models for PSNe are all based on one-dimensional calculations; until now, multidimensional simulations have been scarce. We present the results from multidimensional numerical studies of PSNe with a new radiation-hydrodynamics code, CASTRO and with realistic nuclear reaction networks. We simulate the fluid instabilities that occur in multiple spatial dimensions and discuss how the resulting mixing affects the explosion, mixing, and nucleosynthesis of these supernovae. [Preview Abstract] |
Tuesday, May 3, 2011 11:33AM - 11:45AM |
X7.00005: Magnetic Field-Induced Stability in Two-Flavor Color Superconductivity C. Bhandari, E.J. Ferrer, V. de la Incera It has long been understood that the ground state of a superdense quark system, a Fermi liquid of weakly interacting quarks, is unstable with respect to the formation of diquark condensates. This nonperturbative phenomenon is essentially equivalent to the Cooper instability of conventional BCS superconductivity. As the quark pairs have nonzero color charge, this kind of superconductivity breaks the SU(3) color gauge symmetry, thus it is called color superconductivity. A peculiar feature of spin-zero color superconductivity is the lack of Meissner effect for a combination of the regular electromagnetic field and one of the gluon fields. This combination behaves as an in-medium electromagnetic field and as a consequence, a regular magnetic field can penetrate the color superconductor through its long-range in-medium component. Since the conditions of very high dense matter and very strong magnetic fields are naturally found in neutron stars, the investigations of magnetic field effects in color superconductivity are relevant for astrophysics. In this work we investigate the effects of an external magnetic field in the stability of the ground state of a neutral two-flavor color superconductor. Our results show that a strong magnetic field tends to increase the stability of the ground state, moving it from the unstable gapped region to the stable one. [Preview Abstract] |
Tuesday, May 3, 2011 11:45AM - 11:57AM |
X7.00006: Off-Fermi Shell Nucleons in Superdense Nuclear Matter Michael McGauley, Misak Sargsian Based on recent progress in understanding the nature of two-nucleon short range correlations we performed analysis of world data on inclusive electro-nuclear reactions at large momentum transfer. The analysis allowed us to extract the probabilities of two-nucleon short range correlations for He-3, He-4, C-12, Al-27, Fe-56 and Au-197. Using recent observations on strong dominance of proton-neutron short-range correlations as compared to proton-proton and neutron-neutron correlations we parameterized the obtained probabilities as a function of nuclear density and asymmetry. Using the obtained functional form of the probabilities we estimated the fraction of off-Fermi shell protons and neutrons in the superdense nuclear matter relevant to neutron stars. Our results indicate that starting at 3-4 nuclear saturation densities the protons with fractional densities Xp = 1/9 will populate mostly the high momentum (off-Fermi shell) tail of the momentum distribution while only 20{\%} of the neutrons will be in the high momentum tail. We discuss the implication of our observation on several properties of neutron star cores such as stiffness, phase transitions, cooling, superfluidity and magnetization. [Preview Abstract] |
Tuesday, May 3, 2011 11:57AM - 12:09PM |
X7.00007: ABSTRACT WITHDRAWN |
Tuesday, May 3, 2011 12:09PM - 12:21PM |
X7.00008: Dynamics in the normal ground state of dense relativistic matter in magnetic field Igor Shovkovy, E.V. Gorbar, V.A. Miransky The dynamical generation of the chiral shift parameter $\Delta$ is studied in the normal phase of magnetized relativistic matter. By making use of the gauge invariant point-splitting regularization, we show that the presence of $\Delta$ essentially modifies the form of the axial current, but does not affect the conventional axial anomaly relation. A nonzero chiral shift parameter leads to a relative shift of the longitudinal momenta in the dispersion relations of opposite chirality fermions. This is expected to play an important role in transport and emission properties of matter in various types of compact stars as well as in heavy ion collisions. [Preview Abstract] |
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