arXiv subjects

Tomoyuki Maruyama

Publications and source records attributed to Tomoyuki Maruyama.

At least 37 records · Page 2Linked to original sources

arXiv2015

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.

astro-ph.HE↗

arXiv2014

Deformation Dependence of Breathing Oscillations in Bose - Fermi Mixtures at Zero Temperature

We study the breathing oscillations in bose-fermi mixtures in the axially-symmetric deformed trap of prolate, spherical and oblate shapes, and clarify the deformation dependence of the frequencies and the characteristics of collective oscillations. The collective oscillations of the mixtures in deformed traps are calculated in the scaling method. In largely-deformed prolate and oblate limits and spherical limit, we obtain the analytical expressions of the collective frequencies. The full calculation shows that the collective oscillations become consistent with the analytically-obtained frequencies when the system is deformed into both prolate and oblate regions. The complicated changes of oscillation characters are shown to occur in the transcendental regions around the spherically-deformed region. We find that these critical changes of oscillation characters are explained by the level crossing behaviors of the intrinsic oscillation modes. The approximate expressions are obtained for the level crossing points that determine the transcendental regions. We also compare the results of the scaling methods with those of the dynamical approach.

cond-mat.quant-gas↗

arXiv2014

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 $M > 1.96$ 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.

nucl-th↗

arXiv2014

Breathing Oscillations in Bose - Fermi Mixing Gases with Yb atoms in the Largely Prolate Deformed Traps

We study the breathing oscillations in bose-fermi mixtures with Yb isotopes in the largely prolate deformed trap, which are realized by Kyoto group. We choose the three combinations of the Yb isotopes, Yb170-Yb171, Yb170-Yb173 and Yb174-Yb173, whose boson-fermion interactions are weakly repulsive, strongly attractive and strongly repulsive. The collective oscillations in the deformed trap are calculated in the dynamical time-development approach, which is formulated with the time-dependent Gross-Pitaevskii and the Vlasov equations. We analyze the results in the time-development approach with the intrinsic oscillation modes of the deformed system, which are obtained using the scaling method, and show that the damping and forced-oscillation effects of the intrinsic modes give time-variation of oscillations, especially, in the fermion transverse mode.

cond-mat.quant-gas↗

arXiv2013

Effects of the density-dependent weak form factors on the neutrino reaction via neutral current for the nucleon in nuclear medium and $^{12}$C

The nucleon form factors in free space are usually thought to be modified when a nucleon is bound in a nucleus or immersed in a nuclear medium. We investigate effects of the density-dependent axial and weak-vector form factors on the electro-neutrino ($ν_e$) and anti-electro-neutrino $({\bar ν_e})$ reactions via neutral current (NC) for a nucleon in nuclear medium or $^{12}$C. For the density-dependent form factors, we exploit the quark-meson-coupling (QMC) model, and apply them to the $ν_e$ and ${\bar ν_e}$ induced reactions by NC. About 12% decrease of the total cross section by $ν_e$ reaction on the nucleon is obtained at normal density, $ρ= ρ_0 \sim 0.15 {fm}^{-3} $, as well as about 18% reduction of total $ν_e$ cross section on $^{12}$C, by the modification of the weak form factors of the bound nucleon. However, similarly to the charged current reaction, effects of the nucleon property change in the ${\bar ν}_e$ reaction reduce significantly the cross sections about 30% for the nucleon in matter and $^{12}$C cases. Such a large asymmetry in the ${\bar ν}_e$ cross sections is addressed to originate from the different helicities of ${\bar ν}_e$ and $ν_e$.

nucl-th↗

arXiv2013

Asymmetry in the neutrino and anti-neutrino reactions in a nuclear medium

We study the effect of the density-dependent axial and vector form factors on the electro-neutrino ($ν_e$) and anti-neutrino $({\bar ν}_e)$ reactions for a nucleon in nuclear matter or in $^{12}$C. The nucleon form factors in free space are presumed to be modified for a bound nucleon in a nuclear medium. We adopt the density-dependent form factors calculated by the quark-meson coupling (QMC) model, and apply them to the $ν_e$ and ${\bar ν}_e$ induced reactions with the initial energy $E = $ 8 $\sim$ 80 MeV. We find that the total $ν_e$ cross sections on $^{12}$C as well as a nucleon in nuclear matter are reduced by about 5% at the nuclear saturation density, $ρ_0$. This reduction is caused by the modification of the nucleon structure in matter. Although the density effect for both cases is relatively small, it is comparable with the effect of Coulomb distortion on the outgoing lepton in the $ν$-reaction. In contrast, the density effect on the ${\bar ν}_e$ reaction reduces the cross section significantly in both nuclear matter and $^{12}$C cases, and the amount maximally becomes of about 35% around $ρ_0$. Such large asymmetry in the $ν_e$ and ${\bar ν}_e$ cross sections, which seems to be nearly independent of the target, is originated from the difference in the helicities of ${\bar ν}_e$ and $ν_e$. It is expected that the asymmetry influences the r-process and also the neutrino-process nucleosynthesis in core-collapse supernovae.

nucl-th↗

arXiv2013

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 fielld, B. The asymmetry is 2-4% at the matter density ρ_0 < ρ_B < 3ρ_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.

nucl-th↗

arXiv2011

Breathing oscillations and quasi-low-dimensional structures of weakly-interacting degenerate Fermi gases in highly-anisotropic traps

We theoretically investigate breathing oscillations of weakly-interacting degenerate Fermi gases in highly-anisotropic harmonic oscillator traps. If the traps are not highly anisotropic, the fermions behave as three-dimensional (3D) gases and exhibit the coupled breathing oscillations as studied in a previous paper [T. Maruyama and T. Nishimura, Phys. Rev. A 75 (2007) 033611]; Otherwise the fermions exhibit quasi-low-dimensional (QLD) properties derived from specific structures in their single-particle spectrum, called QLD structures. In the present paper, we focus on effects of the QLD structures on the breathing oscillations of the two-component fermions with symmetric population densities. Here we develop the semi-classical Thomas-Fermi approximation extended to the highly-anisotropic systems and obtain the collective frequencies in the sum-rule-scaling method and perturbation theory. As a result, we reveal that the effects of the QLD structures can not be seen in the transverse modes in the first-order perturbation and appear only in the longitudinal modes with hierarchies reflecting the QLD structures. We also demonstrate time-evolution of the oscillations in the present framework.

cond-mat.other↗

arXiv2011

QHD equation of state for strongly magnetized neutron stars

We investigate the quantum hadrodynamic equation of state for neutron stars (with and without including hyperons) in the presence of strong magnetic fields. The deduced masses and radii are consistent with recent observations of high mass neutron stars even in the case of hyperonic nuclei for sufficiently strong magnetic fields. The calculated adiabatic index and the moments of inertia for magnetized neutron stars exhibit rapid changes with density. This may provide some insight into the mechanism of star-quakes and flares in magnetars.

astro-ph.HE↗

arXiv2010

Free Expansion of a Weakly-interacting Dipolar Fermi Gas

We theoretically investigate a polarized dipolar Fermi gas in free expansion. The inter-particle dipolar interaction deforms phase-space distribution in trap and also in the expansion. We exactly predict the minimal quadrupole deformation in the expansion for the high-temperature Maxwell-Boltzmann and zero-temperature Thomas-Fermi gases in the Hartree-Fock and Landau-Vlasov approaches. In conclusion, we provide a proper approach to develop the time-of-flight method for the weakly-interacting dipolar Fermi gas and also reveal a scaling law associated with the Liouville's theorem in the long-time behaviors of the both gases.

cond-mat.quant-gas↗

arXiv2009

Energy-Dependence of the Nucleon Self-Energies in Off-Mass-Shell Energy Region and the Gamow-Teller Sum-Rule in the Relativistic Hartree-Fock Approach

The relativistic Hartree approximation predicts a deep attractive potential for antinucleon, which largely reduce the threshold energies of the nucleon-antinucleon (N-Nbar) production. This effect has played an important role to explain the quenching of the Gamow-Teller (GT) strength because the quenched strength in the particle-hole excitation is partially taken by the nucleon-antinucleon production. On the other hand antiproton experiments do not reveal deep attractive potential for antinucleon. In this paper we study energy-dependence of the nucleon self-energies in the relativistic Hartree-Fock (RHF) approximation in off-mass-shell states. Then we demonstrate that the antinucleon appearing in low energy observables is in the off-mass-shell energy region and its properties are quite different from that at the on-mass-shell state. Furthermore we show that the quenched amount of the GT strength is not taken only by the \NNbar production but also by the meson production through the imaginary part of the nucleon self-energy in the RHF approximation.

nucl-th↗

arXiv2009

Quadrupole Oscillations in Bose-Fermi Mixtures of Ultracold Atomic Gases made of Yb atoms in the Time-Dependent Gross-Pitaevskii and Vlasov equations

We study quadrupole collective oscillations in the bose-fermi mixtures of ultracold atomic gases of Yb isotopes, which are realized by Kyoto group. Three kinds of combinations are chosen, Yb170-Yb171, Yb170-Yb173 and Yb174-Yb173, where boson-fermion interactions are weakly repulsive, strongly attractive and strongly repulsive respectively. Collective oscillations in these mixtures are calculated in a dynamical time-evolution approach formulated with the time-dependent Gross-Pitaevskii and the Vlasov equations. The boson oscillations are shown to have one collective mode, and the fermions are shown to have the boson-forced and two intrinsic modes, which correspond to the inside- and outside-fermion oscillations for the boson-distributed regions. In the case of the weak boson-fermion interactions, the dynamical calculations are shown to be consistent with the results obtained in the small amplitude approximations as the random phase approximation in early stage of oscillation, but, in later stage, these two approaches are shown to give the different results. Also, in the case of the strong boson-fermion interactions, discrepancies appear in early stage of oscillation. We also analyze these differences in two approaches, and show that they originated in the change of the fermion distributions through oscillation.

cond-mat.other↗

arXiv2007

Dipole Oscillations in Bose - Fermi Mixture in the Time-Dependent Grosspitaevskii and Vlasov equations

We study the dipole collective oscillations in the bose-fermi mixture using a dynamical time-dependent approach, which are formulated with the time-dependent Gross-Pitaevskii equation and the Vlasov equation. We find big difference in behaviors of fermion oscillation between the time-dependent approach and usual approaches such as the random-phase approximation and the sum-rule approach. While the bose gas oscillates monotonously, the fermion oscillation shows a beat and a damping. When the amplitude is not minimal, the dipole oscillation of the fermi gas cannot be described with a simple center-of-mass motion.

cond-mat.other↗

arXiv2006

Coupled Breathing Oscillations of Two-Component Fermion Condensates in Deformed Traps

We investigate collective excitations coupled with monopole and quadrupole oscillations in two-component fermion condensates in deformed traps. The frequencies of monopole and dipole modes are calculated using Thomas-Fermi theory and the scaling approximation. When the trap is largely deformed, these collective motions are decoupled to the transverse and longitudinal breathing oscillation modes. As the trap approaches becoming spherical, however, they are coupled and show complicated behaviors.

cond-mat.other↗

arXiv2005

In-medium Effects in the Eta-Photoproduction through the $S_{11}$ Resonance with the Relativistic Approach

In-medium effects in photon excitation of the S$_{11}$ resonance from nucleon and its decay to $η$-meson using the RMF approach is studied. We examine the in-medium effects by varing the Dirac fields of the nucleon and the S$_{11}$ resonance separately. We obtained a conclusion that the Dirac fields of the nucleon, which reduces the nucleon effective mass, enlarge the width of S$_{11}$ resonance, and small Dirac-fields of the resonance shifts the peak position, and these combined effects can explain the in-medium properties observed in the experimental data for $^{12}$C($γ$,$η$) reaction.

nucl-th↗

arXiv2005

Kaon Condensation and Lambda-Nucleon Loop in the Relativistic Mean-Field Approach

The possibility of kaon condensation in high-density symmetric nuclear matter is investigated including both s- and p-wave kaon-baryon interactions within the relativistic mean-field (RMF) theory. Above a certain density, we have a collective ${\bar K}_s$ state carrying the same quantum numbers as the antikaon. The appearance of the ${\bar K}_s$ state is caused by the time component of the axial-vector interaction between kaons and baryons. It is shown that the system becomes unstable with respect to condensation of $K$-${\bar K}_s$ pairs. We consider how the effective baryon masses affect the kaon self-energy coming from the time component of the axial-vector interaction. Also, the role of the spatial component of the axial-vector interaction on the possible existence of the collective kaonic states is discussed in connection with $Λ$-mixing effects in the ground state of high-density matter. Implications of $K{\bar K}_s$ condensation for high-energy heavy-ion collisions are briefly mentioned.

nucl-th↗

arXiv2005

Nuclear Electromagnetic Current in the Relativistic Approach with the Momentum-Dependent Selfenergies

We define the new description of the electromagnetic current to hold the current conservation in the momentum-dependent Dirac fields from the Ward Takahashi identity. To describe the momentum-dependence we solve the relativistic Hartree-Fock approximation by using the one-pion exchange. In addition we discuss on contribution from the one-pion exchange current and the core polarization. It is shown that this current can reduce the convection current in the isovector case, whose value has been too big due to the small effective mass in the usual relativistic Hartree approximation.

nucl-th↗

arXiv2005

Monopole Oscillations and Dampings in Boson and Fermion Mixture in the Time-Dependent Gross-Pitaevskii and Vlasov Equations

We construct a dynamical model for the time evolution of the boson-fermion coexistence system. The dynamics of bosons and fermions are formulated with the time-dependent Gross-Pitaevsky equation and the Vlasov equation. We thus study the monopole oscillation in the bose-fermi mixture. We find that large damping exists for fermion oscillations in the mixed system even at zero temperature.

cond-mat.soft↗