Chung-Yeol Ryu

Neutron stars in a perturbative f(R) gravity model with strong magnetic fields

In Kaluza-Klein electromagnetism it is natural to associate modified gravity with strong electromagnetic fields. Hence, in this paper we investigate the combined effects of a strong magnetic field and perturbative f(R) gravity on the structure of neutron stars. The effect of an interior strong magnetic field of about 1017?18 G on the equation of state is derived in the context of a quantum hadrodynamics (QHD) equation of state (EoS) including effects of the magnetic pressure and energy along with occupied Landau levels. Adopting a random orientation of interior field domains, we solve the modified spherically symmetric hydrostatic equilibrium equations derived for a gravity model with f(R) = R+?R2. Effects of both the finite magnetic field and the modified gravity are detailed for various values of the magnetic field and the perturbation parameter ? along with a discussion of their physical implications. We show that there exists a parameter space of the modified gravity and the magnetic field strength, in which even a soft equation of state can accommodate a large ( > 2 M?) maximum neutron star mass.

Medium effects of magnetic moments of baryons on neutron stars under strong magnetic fields

We investigate medium effects caused by density-dependent magnetic moments of baryons on neutron stars under strong magnetic fields. If we allow the variation of anomalous magnetic moments (AMMs) of baryons in dense matter under strong magnetic fields, AMMs of nucleons are enhanced to be larger than those of hyperons. The enhancement naturally causes the chemical potentials of the baryons to be large and leads to the increase of the proton fraction. Consequently, it causes the suppression of hyperons, resulting in stiffness of the equation of state. Under the presumed strong magnetic fields, we evaluate the relevant particle populations, the equation of state, and the maximum masses of neutron stars by including density-dependent AMMs and compare them with those obtained from AMMs in free space.

Asymmetric neutrino emission from magnetized proto-neutron star matter including hyperons in relativistic mean field theory

We calculate asymmetric neutrino absorption and scattering cross sections on hot and dense magnetized neutron star matter, including hyperons in fully relativistic mean-field theory. The absorption/scattering cross sections are suppressed/enhanced incoherently in the direction of the magnetic field B=Bz-circumflex. The asymmetry is 2-4% at the matter density {rho}{sub 0{<=}{rho}B{<=}}3{rho}{sub 0} and temperature T{<=}40 MeV for B=2x10{sup 17} G. This asymmetry is comparable to the effects owing to parity violation or asymmetric magnetic field topology proposed for the origin of pulsar kicks.

Rapid spin deceleration of magnetized protoneutron stars via asymmetric neutrino emission

We calculate the spin deceleration of proto-neutron stars by asymmetric neutrino absorption in the context of a fully relativistic mean field theory. We calculate for the first time the spin deceleration of neutron stars due to asymmetric neutrino absorption in a toroidal magnetic field configurations. We find a surprising effect that the deceleration can much larger for asymmetric neutrino absorption in a toroidal magnetic field than the usually presumed braking due to magnetic dipole radiation. This may explain the observation that magnetars appear to have had a more rapid deceleration in the past.

Quantum Field Theoretic Treatment of Pion Production via Proton Synchrotron Radiation in Strong Magnetic Fields: Effects of Landau Levels

We study pion production from proton synchrotron radiation in the presence of strong magnetic fields. We derive the exact proton propagator from the Dirac equation in a strong magnetic field by explicitly including the anomalous magnetic moment. In this exact quantum-field approach the magnitude of pion synchrotron emission turns out to be much smaller than that obtained in the semi-classical approach. However, we also find that the anomalous magnetic moment of the proton greatly enhances the production rate about by two order magnitude.

Neutrino Emission from Magnetized Proto-Neutron Stars in Relativistic Mean Field Theory

Tomoyuki Maruyama, 2, 3 Nobutoshi Yasutake, Myung-Ki Cheoun, 3 Jun Hidaka, Toshitaka Kajino, 6 Grant J. Mathews, and Chung-Yeol Ryu College of Bioresource Sciences, Nihon University, Fujisawa 252-8510, Japan Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai 319-1195, Japan National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan Research Institute for the Early Universe, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan Department of Physics, Soongsil University, Seoul, 156-743, Korea Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan Center of Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA (Dated: December 21, 2013)

Hyperon and nuclear symmetry energy in the neutron star

In this work, masses and radii of neutron stars are considered to investigate the effect of nuclear symmetry energy on astrophysical observables. A relativistic mean-field model with density-dependent meson-baryon coupling constants is employed in describing the equation of state of dense nuclear matter, and the density dependencies of the symmetry energies are quoted from the recent phenomenological formulas obtained from heavy-ion data at subnuclear saturation densities. Since hyperons can take part in the {beta}-equilibrium of the dense matter inside neutron stars, we include hyperons in our estimation and their roles are discussed in combination with that of the nuclear symmetry energy.

Asymmetric neutrino production in strongly magnetized proto-neutron stars

We calculate the neutrino production cross-section through the direct URCA process in proto-neutron star matter in the presence of a strong magnetic field. We assume isoentropic conditions and introduce a new equation of state parameter-set in the relativistic mean-field approach that can reproduce neutron stars with

Magnetic moments of octet baryons at finite density and temperature

M > 1.96

MASS RELATIONS OF NUCLEONS AND MESONS UNDER SU(2) SYMMETRY BREAKING IN A GAUGED LINEAR SIGMA MODEL

M