Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session DL: Mini-Symposium on Nuclear Matter in Neutron Stars I (EoS and Structure) |
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Chair: Takashi Nakamura, Tokyo Institute of Technology Room: Kona 4 |
Thursday, October 9, 2014 9:00AM - 9:30AM |
DL.00001: Neutron star matter equation of state: current status and challenges Invited Speaker: Akira Ohnishi Neutron star matter has a variety of constituents and structures depending on the density; neutron-rich nuclei surounded by electrons and drip neutrons in the crust, pasta nuclei at the bottom of inner crust, and uniform isospin-asymmetric nuclear matter in a superfluid state in the outer core. In the inner core, the neutron Fermi energy becomes so large that exotic constituents such as hyperons, mesons and quarks may emerge. Radioactive beam and hypernuclear experiments provide information on the symmetry energy and superfluidity in the crust and outer core and on the hyperon potentials in the inner core, respectively. Cold atom experiments are also helpful to understand pure neutron matter, which may be simulated by the unitary gas. An equation of state (EOS) constructed based on these laboratory experiments has to be verified by the astronomical observations such as the mass, radius, and oscillations of neutron stars. One of the key but missing ingredients is the three-baryon interactions such as the hyperon-hyperon-nucleon ($YYN$) interaction. $YYN$ interaction is important in order to explain the recently discovered massive neutron stars consistently with laboratory experiments. We have recently found that the $\Lambda\Lambda$ interaction extracted from the $\Lambda\Lambda$ correlation at RHIC is somewhat stronger than that from double $\Lambda$ hypernuclei. Since these two interactions corresponds to the vacuum and in-medium $\Lambda\Lambda$ interactions, respectively, the difference may tell us a possible way to access the $YYN$ interaction based on experimental data. In the presentation, after a review on the current status of neutron star matter EOS studies, we discuss the necessary tasks to pin down the EOS. We also present our recent study of $\Lambda\Lambda$ interaction from correlation data at RHIC. [Preview Abstract] |
Thursday, October 9, 2014 9:30AM - 9:45AM |
DL.00002: Roles of light nuclei in dense matter for supernova explosions Kosuke Sumiyoshi, Shun Furusawa, Hiroki Nagakura, Hideyuki Suzuki, Shoichi Yamada We report on appearance of light nuclei in supernova cores and its possible roles for the explosion dynamics of core-collapse supernovae. We show that the light nuclei (deuterons, tritons and helium isotopes) are abundant in hot and dense matter for a certain layer of the supernova cores. The extended framework of the relativistic mean field theory with mixture of nuclei has been applied to construct the data of equation of state for supernova simulations. Medium and temperature effects are taken into account for bulk and shell energies of nuclei. Such abundant light-nuclei may act as additional agents of neutrino cooling and heating in the supernova core. Additional neutrino reactions with light nuclei may assist or harm shock propagation for the successful explosions. We demonstrate that neutrino absorptions may have impact on revival of the shock wave by numerical simulations. The time evolutions of shockwave, which is initially stalled, in 2D supernova cores have been studied by following hydrodynamics with the neutrino heating processes. We found that neutrino heating via light nuclei can be influential for the critical situation for the revival of shock wave. We discuss also novel roles of neutrino reactions with light nuclei in neutrino emitting regions. [Preview Abstract] |
Thursday, October 9, 2014 9:45AM - 10:00AM |
DL.00003: Variational study of the supernova equation of state with realistic nuclear forces Hajime Togashi, Yuta Takehara, Sachiko Yamamuro, Ken'ichiro Nakazato, Hideyuki Suzuki, Kohsuke Sumiyoshi, Masatoshi Takano We construct a new nuclear equation of state (EOS) for numerical simulations of core-collapse supernovae (SNe) with the realistic nuclear forces. For this purpose, we first constructed the EOS for uniform matter based on the Argonne v18 two-body potential and the Urbana IX three-body potential with the cluster variational method. The obtained free energies agree well with those by the more sophisticated Fermi Hypernetted Chain variational method. The symmetry energy of our EOS is smaller than that of the Shen EOS, and masses and radii of neutron stars with the present EOS are consistent with the observational data. In order to complete the SN-EOS, we are constructing an EOS for non-uniform matter in the Thomas-Fermi approximation. The thermodynamic quantities obtained so far are quite reasonable, and the phase diagrams of nuclear matter are similar to those of the Shen EOS. To our knowledge, this is the first SN-EOS based on the bare nuclear forces. In this talk, we systematically compare the thermodynamic quantities of the present EOS with those of the Shen EOS. Furthermore, as the first step of the application to SN simulations, we will examine the properties of central core from the collapse of a progenitor with our EOS. [Preview Abstract] |
Thursday, October 9, 2014 10:00AM - 10:15AM |
DL.00004: Neutrino Emissivities from Deuteron-Breakup and Formation in Supernovae Satoshi Nakamura, Shota Nasu, Kohsuke Sumiyoshi, Toru Sato, Fred Myhrer, Kuniharu Kubodera Recently it was pointed out that there are abundant light nuclei, such as deuteron, triton and helium, in supernova environment. An interesting question is how much neutrino emissions from these light nuclei affect supernova mechanism. To address this question through a supernova simulation, neutrino emissivities from these light nuclei are necessary input. The deuteron is the simplest nucleus, and occupy a substantial portion of the light nuclei abundance. Thus in this work, we study neutrino emissions from electron/positron capture on the deuteron and the nucleon-nucleon fusion processes in the surface region of a supernova core. We evaluate these weak processes using one-nucleon impulse current supplemented by two-nucleon exchange currents, and nuclear wave functions generated by a high precision nucleon-nucleon potential. We present the neutrino emissivities from the deuteron calculated for typical profiles of core-collapsed supernovae. These novel neutrino emissivities are compared with the standard neutrino emission mechanisms. We find that the neutrino emissivity due to the electron capture on the deuteron is comparable to that on the proton in the deuteron abundant region. We discuss implications of the new channels involving deuterons for the supernova mechanism. [Preview Abstract] |
Thursday, October 9, 2014 10:15AM - 10:30AM |
DL.00005: The imprint of strong neutron star crust neutrino cooling on superbursts and transient outbursts Edward Brown The temperature in the outer crust (densities $<10^{11}\,\mathrm{g\,cm^{-3}}$) of an accreting neutron star determines the ignition conditions for superbursts---rare, energetic explosions in the accreted neutron star envelope---and the cooling of the surface layers when the accretion of matter halts. Recently, Schatz et al.\ discovered that neutrino emission from cycles of electron captures and $\beta^-$ decays on neutron-rich nuclei at densities $\approx 10^{10}\,\mathrm{g\,cm^{-3}}$ can efficiently cool the neutron star crust and thermally decouple the neutron star envelope from the deeper interior. Motivated by this work, we report here our preliminary findings from using time-dependent models of an accreting neutron star's crust, which include this cooling, to explore its impact on superburst ignition and the cooling of quasi-persistent transients. [Preview Abstract] |
Thursday, October 9, 2014 10:30AM - 10:45AM |
DL.00006: Constraints on neutron-star mass-radius relation by the EOS derived from realistic interactions Ngo Quang Thin, Shoji Shinmura Using new versions of realistic baryon-baryon interactions, we determine the EOS of high-density beta-stable baryonic matter and calculate the mass-radius relation of neutron stars by solving the TOV equation. We consider the three regions in neutron stars. The first region is the crust of neutron stars, which is not important for the mass-radius relation. The second is the region dominated by hadronic interactions with densities lower than n-times of the nuclear normal density, where n is a variable. In this region, we assume additionally a theoretical three-body force. Third region is that with densities higher than n-times of the normal density. This region is described by the EOS allowed theoretically. Our aim in this talk is to impose constraints on the mass-radius relation of neutron stars based on the EOS in the second region. [Preview Abstract] |
Thursday, October 9, 2014 10:45AM - 11:00AM |
DL.00007: Finding of a new nuclear matter parameter characterizing low-mass neutron stars Hajime Sotani, Kei Iida, Kazuhiro Oyamatsu, Akira Ohnishi Neutron star could be a suitable laboratory to see the physics under extreme state. In practice, it is expected that the observations of neutron stars enable us to constrain the equation of state (EOS) of neutron star matter. However, the EOS for density region a few times lager than the saturation density is still very uncertain. Thus, the direct discussion of EOS may not be so easy, even if the mass and radius of neutron stars would be observationally determined. On the other hand, in the case of a low-mass neutron star whose central density is relatively small, the parameters characterizing the EOS of nuclear matter near the saturation point should become important to describe such an object, where one could not care the uncertainties in high density EOS. So, we systematically investigate the dependence of the mass-radius relations of low-mass neutron stars on the saturation parameters in an EOS model that is consistent with empirical masses and radii of stable nuclei. Then, we are successful to find a suitable parameter describing low-mass neutron stars, which is the combination of the parameters that characterize the density dependence of the symmetry energy ($L$) and the incompressibility of nuclear matter ($K_0$). [Preview Abstract] |
Thursday, October 9, 2014 11:00AM - 11:15AM |
DL.00008: Neutron Star EOS and Symmetry Energy in RMF model with three-body couplings Kohsuke Tsubakihara, Akira Ohnishi, Toru Harada Neutron Star EOS(NS-EOS) is one of most interesting topics not only in astrophysics but also in nuclear physics. Symmetry energy in nuclear system and the emergence of hyperons in dense matter are key ingredients to investigate NS-EOS theoretically. We introduced $n=3$ three-body couplings to RMF model and examine how valid they are to give reasonable descriptions of nuclear/hypernuclear properties. We have been able to obtain the quantitatively enough fit of both the bulk properties of finite nuclear systems and consistent symmetry energy with the one deduced from recent observations simultaneously. In this presentation, we present the results of hadronic star matter EOS, M-R relation, possibility of appearance of $\Sigma^-$ in NS-EOS providing we fix isovector-vector couplings by fitting $\Sigma^-$ atomic shift data, and so on. [Preview Abstract] |
Thursday, October 9, 2014 11:15AM - 11:30AM |
DL.00009: Microscopic Calculations of Neutron Matter, Symmetry Energy and Neutron Stars Stefano Gandolfi Recent advances in experiments of the symmetry energy of nuclear matter and in neutron star observations yield important new insights on the equation of state of neutron matter at nuclear densities. In this regime the EOS of neutron matter plays a critical role in determining the mass-radius relationship for neutron stars. We show how microscopic calculations of neutron matter, based on realistic two- and three-nucleon forces, make clear predictions for the relation between the isospin-asymmetry energy of nuclear matter and its density dependence, and the maximum mass and radius for a neutron star. On the other hand, we show that important information on the equation of state can be extracted from neutron star observations. [Preview Abstract] |
Thursday, October 9, 2014 11:30AM - 11:45AM |
DL.00010: An explicit energy functional for neutron matter taking into account the spin-orbit force Masatoshi Takano, Kohei Kato We have been studying the variational method with an explicit energy functional for infinite nuclear matter. In this method, we construct an energy functional which expresses the energy per nucleon of nuclear matter explicitly with various two-body distribution functions. Once a reliable energy expression is obtained, the Euler-Lagrange equations for those distribution functions are derived analytically, and the fully minimized energies are calculated relatively easily. So far, we have proposed the energy expressions with two-body central and tensor forces. The calculated energies with the AV6' potential are reasonable as compared with those obtained with the Monte Carlo methods. Furthermore, in the last JPS meeting, we reported on an energy expression for neutron matter including two-body spin-orbit forces: The preliminary results of the energy with the AV8' potential are in good agreement with those with the AFDMC calculations. In this presentation, we will report on an extension of the energy functional for neutron matter so as to treat the repulsive part of the UIX three-body potential. An extension of this variational method to hot nuclear matter will also be reported. [Preview Abstract] |
Thursday, October 9, 2014 11:45AM - 12:00PM |
DL.00011: Large scale molecular dynamics simulations of nuclear pasta C.J. Horowitz, D. Berry, C. Briggs, M. Chapman, E. Clark, A. Schneider We report large-scale molecular dynamics simulations of nuclear pasta using from 50,000 to more than 3,000,000 nucleons. We use a simple phenomenological two-nucleon potential that reproduces nuclear saturation. We find a complex ``nuclear waffle'' phase in addition to more conventional rod, plate, and sphere phases. We also find long-lived topological defects involving screw like dislocations that may reduce the electrical conductivity and thermal conductivity of lasagna phases. From MD trajectories we calculate a variety of quantities including static structure factor, dynamical response function, shear modulus and breaking strain. [Preview Abstract] |
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