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We study the quantum hadrodynamic (QHD) equation of state for neutron stars (with and without including hyperons) in the presence of strong magnetic fields. The calculated adiabatic index for magnetized neutron stars based on the QHD model exhibit rapid changes with density. This may provide some insight into the mechanism of star-quakes and flares in magnetars. We also investigate the strong magnetic field effects on the moments of inertia of neutron stars. The change of the moments of inertia associated with emitted magnetic flares is shown to match well with observed glitches in some magnetars. In our QHD model, the deduced masses and radii of neutron stars without hyperons are consistent with recent observations of high mass neutron stars, while those with hyperons turn out to be less than the recent high mass neutron star.

See paper for full list of authors; The Korea Rare Isotope Accelerator, currently referred to as KoRIA, is briefly presented. The KoRIA facility is aimed to enable cutting-edge sciences in a wide range of fields. It consists of a 70 kW isotope separator on-line (ISOL) facility driven by a 70 MeV, 1 mA proton cyclotron and a 400 kW in-flight fragmentation (IFF) facility. The ISOL facility uses a superconducting (SC) linac for post-acceleration of rare isotopes up to about 18 MeV/u, while the SC linac of IFF facility is capable of accelerating uranium beams up to 200 MeV/u, 8 pμA and proton beams up to 600 MeV, 660 μA. Overall features of the KoRIA facility are presented with a focus on the accelerator design.

We investigate the structure of neutron star within the framework of the quark-meson coupling model, considering hyperons and kaon condensation. In order to compare the EoS with that from quark matter, the MIT bag model is used. We calculate the mass and radius of a neutron star by using Tolman-Oppenheimer-Volkov equations.

We evaluate mass differences between a neutron and a proton, and between a charged and a neutral meson by using a gauged linear sigma model retaining the chiral SU (2) L × SU (2) R × U (1)V symmetry. Masses of nucleons and relevant mesons are generated through the spontaneous and the explicit chiral symmetry breaking. Since our Lagrangian includes explicitly SU(2) isospin symmetry breaking term, it enables us to simultaneously consider the mass differences of a neutron and a proton, and a charged meson and a neutral one. Their reciprocal relations of the mass differences are also derived, where radiative corrections due to electromagnetic interactions are deliberately taken into account to exactly obtain the isospin symmetry breaking effect in the particle mass differences.

We study pion production from proton synchrotron radiation in the presence of strong magnetic fields by using the exact proton propagator in a strong magnetic field and 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 semiclassical approach. However, we also find that the anomalous magnetic moment of the proton greatly enhances the production rate about by 2 orders of magnitude.

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 $M > 1.96$ M$_\odot$ as required by observations. We find that the production process increases the flux of emitted neutrinos along the direction parallel to the magnetic field and decreases the flux in the opposite direction. This means that the neutrino flux asymmetry due to the neutrino absorption and scattering processes in a magnetic field becomes larger by the inclusion of the neutrino production process., 9 pages, 3 figures

Tomoyuki Maruyama1, Jun Hidaka2, Toshitaka Kajino2, Nobutoshi Yasutake3, Takami Kuroda2, Myung-Ki Cheoun4, Chung-Yeol Ryu5 and Grant J. Mathews6 1College of Bioresource Sciences, Nihon University, Fujisawa 252-8510, Japan 2National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan 3Department of Physics, Chiba Institute of Technology, Narashino 275-0023, Japan 4Department of Physics, Soongsil University, Seoul, 156-743, Korea 5General Education Curriculum Center, Hanyang University, Seoul, 133-791, Korea 6Center of Astrophysics, University of Notre Dame, Notre Dame, IN 46556, USA

We addressed possible ambiguities on the properties of neutron stars (NSs) estimated in theoretical sides. First, roles of hyperons inside the NS are discussed through various relativistic mean field (RMF) theories. In particular, the extension of SU(6) spin-flavor symmetry to SU(3) flavor symmetry is shown to give rise to the increase of hyperon threshold density, similarly to the Fock term effects in RMF theories. As a result, about 2.0 solar mass is obtained with the hyperons. Second, the effect by the modified f(R) gravity, which leaves a room for the dark energy in the Einstein equation to be taken into account, is discussed for the NS in a strong magnetic field (MF). Our results show that the modified gravity with the Kaluza-Klein electro-magnetism theory expanded in terms of a length scale parameter may reasonably describe the NS in strong MF, so called magnetar. Even the super-soft equation of state is shown to be revived by the modified f(R) gravity.

We calculate the neutrino production cross-section in the proto-neutron-star matter under a strong magnetic field in the relativistic mean-field approach. We introduce a new parameter-set which can reproduce the 1.96 solar mass neutron star. We find that the production process increases emitted neutrinos along the direction parallel to the magnetic field and decrease those along its opposite direction. It means that resultant asymmetry due to the neutrino absorption and scattering process in the magnetic field becomes larger by the addition of the neutrino production process.

We calculate neutrino scattering and absorption on the hot and dense neutron-star matter with hyperons under the strong magnetic field using a perturbative approach. We find that the absorption cross-sections show a remarkable angular dependence. Its strength is reduced in the direction parallel to the magnetic field and enhanced in the opposite direction. This asymmetric variation becomes maximally 2.2% of entire neutrino momentum when the magnetic field is assumed as about 2 × 1017G. Since the pulsar kick after the supernova explosion may have relationships to this asymmetry, detailed discussions about the pulsar kick and the asymmetry are presented with the comparison to the observed kick velocities in a fully relativistic approach.

We make a perturbative calculation of neutrino scattering and absorption in hot and dense hyperonic neutron-star matter in the presence of a strong magnetic Field. We calculate that the absorption cross-sections in a fully relativistic mean-field theory. We find that there is a remarkable angular dependence, i.e. the neutrino absorption strength is reduced in a direction parallel to the magnetic Field and enhanced in the opposite direction. This asymmetry in the neutrino absorption is estimated to be as much as 2.2 % of the entire neutrino momentum for an interior magnetic Field of 2 x 10^{17} G. The pulsar kick velocities associated with this asymmetry are shown to be comparable to observed velocities., Comment: arXiv admin note: substantial text overlap with arXiv:1009.0976

We investigate the structure of a proto-neutron star with trapped neutrinos by using quantum hadrodynamics. Ratios of the trapped neutrinos and corresponding leptons to the baryons are usually assumed to be constant. But relevant reactions associated with the $\ensuremath{\beta}$ equilibrium could be sensitive to the given density and temperature. By adopting a phenomenological lepton density that is smeared near the surface, we calculate and discuss populations of baryons and leptons, equations of state, and the mass-radius relation of a proto-neutron star in an isentropic process.

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 fielld, B. The asymmetry is 2-4% at the matter density ��_0 < ��_B < 3��_0 and temperature T < 40 MeV for B=2 X 10^{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., 9 pages, 3 figure

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.

We investigate the effect of a strong magnetic field on the structure of neutron stars in a model with perturbative $f(R)$ gravity. The effect of an interior strong magnetic field of about $10^{17 \sim 18}$ G on the equation of state is derived in the context of a quantum hadrodynamics (QHD) model. We solve the modified spherically symmetric hydrostatic equilibrium equations derived for a gravity model with $f(R)=R+\alpha R^2$. Effects of both the finite magnetic field and the modified gravity are detailed for various values of the magnetic field and the perturbation parameter $\alpha$ 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$_\odot$) maximum neutron star mass through the modified mass-radius relation.

We investigate the change of magnetic moments of octet baryons in nuclear matter at a finite density and temperature. Quark-meson coupling models are employed in describing properties of octet baryons and their interactions. Magnetic moments of octet baryons are found to increase non-negligibly as density and temperature increase, and we find that temperature dependence can be strongly correlated with the quark-hadron phase transition. Model dependence is also examined by comparing the results from the quark-meson coupling (QMC) model to those by the modified QMC (MQMC) model where the bag constant is assumed to depend on density. Both models predict sizable dependence on density and temperature, but the MQMC model shows a more drastic change of magnetic moments. Feasible changes of the nucleon mass by strong magnetic fields are also reported in the given models., Comment: 12 pages