Hiroshi Toki

Relativistic equation of state of nuclear matter for supernova and neutron star

Abstract We construct the equation of state (EOS) of nuclear matter using the relativistic mean field (RMF) theory in the wide density, temperature range with various proton fractions for the use of supernova simulation and the neutron star calculations. We first construct the EOS of homogeneous nuclear matter. We use then the Thomas-Fermi approximation to describe inhomogeneous matter, where heavy nuclei are formed together with free nucleon gas. We discuss the results on free energy, pressure and entropy in the wide range of astrophysical interest. As an example, we apply the resulting EOS on the neutron star properties by using the Oppenheimer-Volkoff equation.We construct the equation of state (EOS) of nuclear matter using the relativistic mean field (RMF) theory in the wide density, temperature range with various proton fractions for the use of supernova simulation and the neutron star calculations. We first construct the EOS of homogeneous nuclear matter. We use then the Thomas-Fermi approximation to describe inhomogeneous matter, where heavy nuclei are formed together with free nucleon gas. We discuss the results on free energy, pressure and entropy in the wide range of astrophysical interest. As an example, we apply the resulting EOS on the neutron star properties by using the Oppenheimer-Volkoff equation.

Revelation of thick neutron skins in nuclei

Abstract Thick neutron skins (∼ 0.9 fm) have been verified for the first time in 6He and 8He nuclei from a combined analysis of the interaction and the fragmentation cross sections of 4,6,8He incident reactions at 800A MeV. A relativistic mean field (RMF) model was applied to 6He and 8He nuclei and shown to reproduce the neutron skin thicknesses very well. It is also shown that the RMF model predicts a gross linear dependence of the neutron skin thickness on the difference between the proton and the neutron Fermi energy in a wide range of nuclei. Possible observations of thick neutron skins in other nuclei, in particular in Na isotopes, are also discussed.

Relativistic Equation of State of Nuclear Matter for Supernova Explosion

We construct the equation of state (EOS) of nuclear matter at finite temperature and density with various proton fractions within the relativistic mean field (RMF) theory for the use in the supernova simulations. The Thomas-Fermi approximation is adopted to describe the non-uniform matter where we consider nucleus, alpha-particle, proton and neutron in equilibrium. We treat the uniform matter and non-uniform matter consistently using the RMF theory. We tabulate the outcome as the pressure, free energy, entropy etc, with enough mesh points in wide ranges of the temperature, proton fraction, and baryon mass density.

Postbounce Evolution of Core-Collapse Supernovae: Long-Term Effects of the Equation of State

We study the evolution of a supernova core from the beginning of the gravitational collapse of a 15 M☉ star up to 1 s after core bounce. We present results of spherically symmetric simulations of core-collapse supernovae by solving general relativistic ν-radiation hydrodynamics in the implicit time differencing. We aim to explore the evolution of shock waves in the long term and investigate the formation of proto-neutron stars together with supernova neutrino signatures. These studies are done to examine the influence of the equation of state (EOS) on the postbounce evolution of shock waves in the late phase and the resulting thermal evolution of proto-neutron stars. We compare two sets of EOSs, namely, those by Lattimer and Swesty (LS-EOS) and by Shen et al. (SH-EOS). We found that, for both EOSs, the core does not explode and the shock wave stalls similarly in the first 100 ms after bounce. A revival of the shock wave does not occur even after a long period in either case. However, the recession of the shock wave appears different beyond 200 ms after bounce, having different thermal evolution of the central core. A more compact proto-neutron star is found for LS-EOS than SH-EOS with a difference in the central density by a factor of ~2 and a difference of ~10 MeV in the peak temperature. The resulting spectra of supernova neutrinos are different to an extent that may be detectable by terrestrial neutrino detectors.

Asymmetric rotor model for decoupled bands in transitional odd-mass nuclei

Abstract The high-spin states in transitional odd-mass nuclei are studied in terms of an odd quasi-particle coupled to an asymmetric rotor with a variable moment of inertia (VMI). In order to take into account the VMI, the basis states are expanded in terms of the core eigenfunctions. Excitation energies, quadrupole moments, magnetic moments, B (E2) values and B (M1) values are calculated and compared with the experimental data for nuclei in Au and La regions. On comparison with other descriptions it is found that the treatment with VMI provides a more satisfactory explanation of the data.

Photoproduction of the Lambda(1405) on the proton and nuclei

Abstract We study the γp → K + Λ (1405) reaction at energies close to threshold using a chiral unitary model where the resonance is generated dynamically from K − p interaction with other channels constructed from the octets of baryons and mesons. Predictions are made for cross sections into several channels and it is shown that the detection of the K + is sufficient to determine the shape and strength of the Λ (1405) resonance. The determination of the resonance properties in nuclei requires instead the detection of the resonance decay channels. Pauli blocking effects on the resonance, which have been shown to be very important for the resonance at rest in the nucleus, are irrelevant here where the resonance is produced with a large momentum. The nuclear modifications here would thus offer information on the resonance and K − nucleus dynamics complementary to the one offered so far by K − atoms.

Radiative decay of ρ0 and φ mesons in a chiral unitary approach

Abstract We study the ρ 0 and φ decays into π + π − γ , π 0 π 0 γ and φ into π 0 ηγ using a chiral unitary approach to deal with the final state interaction of the MM system. The final state interaction modifies only moderately the large momenta tail of the photon spectrum of the ρ 0 → π + π − γ decay. In the case of φ decay the contribution to π + π − γ and π 0 π 0 γ decay proceeds via kaonic loops and gives a distribution of ππ invariant masses in which the f 0 (980) resonance shows up with a very distinct peak. The spectrum found for φ → π 0 π 0 γ decay agrees with the recent experimental results obtained at Novosibirsk. The branching ratio for φ → π 0 ηγ , dominated by the a 0 (980), is also in agreement with recent Novosibirsk results.

Masses, deformations and charge radii: Nuclear ground-state properties in the relativistic mean field model

We perform a systematic study of the ground-state properties of all the nuclei from the proton drip line to the neutron drip line throughout the periodic table employing the relativistic mean field model. The TMA parameter set is used for the mean-field Lagrangian density, and a state-dependent BCS method is adopted to describe the pairing correlation. The ground-state properties of a total of 6969 nuclei with Z, N ≥ 8a ndZ ≤ 100 from the proton drip line to the neutron drip line, including the binding energies, the separation energies, the deformations, and the rms charge radii, are calculated and compared with existing experimental data and those of the FRDM and HFB-2 mass formulae. This study provides the first complete picture of the current status of the descriptions of nuclear ground-state properties in the relativistic mean field model. The deviations from existing experimental data indicate either that new degrees of freedom are needed, such as triaxial deformations, or that serious effort is needed to improve the current formulation of the relativistic mean field model.

Mass dependence of inclusive nuclear φ photoproduction

Abstract Based on a prior determination of the φ selfenergy in a nuclear medium we perform a theoretical study of inclusive φ photoproduction in nuclei, looking at the A dependence of the cross sections for different φ momenta. We find sizeable reductions in the nuclear cross sections with respect to the elementary one, using a φ selfenergy which implies a width about six times the free one at normal nuclear density. The calculations are done to match the set up for an ongoing experiment at SPring8/Osaka which should provide valuable information on the renormalization of the φ properties in nuclei.

Non-axial deformations and the odd parity states in the even Pt and Hg isotopes

Abstract The semi-decoupled model, which was proposed in a previous publication with the aim of describing the frequently appearing odd parity bands in even nuclei with spin sequence ΔI = 2, is extended to the case of a γ-deformed core. The extended model is applied in a calculation of the yrast odd parity states of the even Pt and Hg isotopes, assuming respectively γ = 30° and γ = 60° for the two elements. Characteristic differences between the appearance of the odd parity bands of the two elements are well accounted for by the model and may be understood in terms of simple qualitative features of the model system. An explanation of the 10 − isomers observed in 190, 192 Pt is also provided by the model.