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Lee, T.-G.*; Yasutake, Nobutoshi*; Maruyama, Toshiki; Tatsumi, Toshitaka*
Proceedings of Science (Internet), 8 Pages, 2017/05
Muto, Takumi*; Maruyama, Toshiki; Tatsumi, Toshitaka*
JPS Conference Proceedings (Internet), 14, p.020809_1 - 020809_3, 2017/02
Times Cited Count：0 Percentile：100Noda, Tsuneo*; Hashimoto, Masaaki*; Matsuo, Yasuhide*; Yasutake, Nobutoshi*; Maruyama, Toshiki; Tatsumi, Toshitaka*
JPS Conference Proceedings (Internet), 14, p.020805_1 - 020805_3, 2017/02
Times Cited Count：0 Percentile：100Lee, T.-G.*; Nishiyama, Kazuya*; Yasutake, Nobutoshi*; Maruyama, Toshiki; Tatsumi, Toshitaka*
JPS Conference Proceedings (Internet), 14, p.020808_1 - 020808_3, 2017/02
Times Cited Count：0 Percentile：100Yasutake, Nobutoshi*; Chen, H.*; Maruyama, Toshiki; Tatsumi, Toshitaka*
Journal of Physics; Conference Series, 665(1), p.012068_1 - 012068_4, 2016/01
Times Cited Count：4 Percentile：10.76Maruyama, Toshiki
Acta Astronomica Sinica, 56(Suppl.), p.40 - 42, 2015/11
We discuss the effects of inhomogeneous structure of nuclear matter in neutron stars. The inhomogeneous matter due to the first-order phase transition is widely studied. Its effect on the bulk properties are often reported to be minor. However, we stress that the chemical compositions largely affected by the inhomogeneous structures.
Noda, Tsuneo*; Yasutake, Nobutoshi*; Hashimoto, Masaaki*; Maruyama, Toshiki; Tatsumi, Toshitaka*; Fujimoto, Masayuki*
Acta Astronomica Sinica, 56(Suppl.), p.52 - 54, 2015/11
We show a scenario for the cooling of compact stars considering the central source of Cassiopeia A (Cas A). The Cas A observation shows that the central source is a compact star with high effective temperature, and it is consistent with the cooling without exotic phases. The Cas A observation also gives the mass range of 
. It may conflict with the current cooling scenarios of compact stars that heavy stars show rapid cooling. We include the effect of the color superconducting (CSC) quark matter phase on the thermal evolution of compact stars. We assume the gap energy of CSC quark phase is large (
MeV), and we simulate the cooling of compact stars. We present cooling curves obtained from the evolutionary calculations of compact stars: while heavier stars cool slowly, and lighter ones indicate the opposite tendency.
Muto, Takumi*; Maruyama, Toshiki; Tatsumi, Toshitaka*
Acta Astronomica Sinica, 56(Suppl.), p.43 - 45, 2015/11
Coexistence of kaon condensation and hyperons, which may be realized in neutron stars, is investigated on the basis of the relativistic mean-field theory combined with the effective chiral Lagrangian. It is shown that kaon-condensed phase in hyperon-mixed matter is plausible, but it leads to significant softening of the equation of state (EOS). We discuss indispensable effects which make the EOS stiffer so as to be consistent with recent neutron-star observations.
Yasutake, Nobutoshi*; Benic, S.*; Blaschke, D.*; Maruyama, Toshiki; Tatsumi, Toshitaka*
Acta Astronomica Sinica, 56(Suppl.), p.85 - 87, 2015/11
We study quark-hadron phase transition in neutron stars. The finite-size effects of mixed-phase structure should be taken into account in the phase transition of multi-component system. The phase transition strongly depends on the models for quark and hadron matter, surface tension, neutrino fraction, and temperature. We find that with strong surface tension the equation of state (EOS) becomes similar to that of a Maxwell construction, while weak surface tension yields bulk Gibbs condition. We also find that the mass-radius relation obtained by our EOS is consistent to the observation.
Muto, Takumi*; Maruyama, Toshiki; Tatsumi, Toshitaka*
EPJ Web of Conferences, 73, p.05007_1 - 05007_5, 2014/06
Times Cited Count：1 Percentile：53.12Possible coexistence of antikaons and hyperons in nuclei and in neutron stars is investigated based on the same interaction model within the relativistic mean-field theory. It is shown that the ground state of multi-strangeness nuclei is given by multi-hypernuclei without bound 
mesons. In neutron stars, on the other hand, kaon condensation appears in hyperon-mixed matter for a moderate potential depth, but it leads to significant softening of the equation of state. Some repulsive effect at high density should be taken into account so as to be consistent with recent observations of massive neutron stars.
Yasutake, Nobutoshi*; Lastowiecki, R.*; Benic, S.*; Blaschke, D.*; Maruyama, Toshiki; Tatsumi, Toshitaka*
Physical Review C, 89(6), p.065803_1 - 065803_10, 2014/06
Times Cited Count：62 Percentile：2.15(Physics, Nuclear)Okamoto, Minoru*; Maruyama, Toshiki; Yabana, Kazuhiro*; Tatsumi, Toshitaka*
Physical Review C, 88(2), p.025801_1 - 025801_10, 2013/08
Times Cited Count：33 Percentile：9.39(Physics, Nuclear)In neutron star crust, non-uniform structure of nuclear matter is expected, which is called the "pasta" structure. From the recent studies of giant flares in magnetars, these structures might be related to some observables and physical quantities of the neutron star crust. To investigate the above quantities, we have numerically explored the pasta structures with a fully three-dimensional geometry and have studied the properties of low-density nuclear matter, based on the relativistic mean-field model and the Thomas-Fermi approximation. We have observed typical pasta structures for fixed proton number-fraction and droplet and rod for cold catalyzed matter. We have also explored the crystalline configuration of "pasta". Although it was believed that spherical nuclei (droplets) form a body-centred cubic lattice as a ground state, we have shown that a face-centred cubic lattice is energetically more favored than body-centred cubic lattice near the transition density to rod.
Sotani, Hajime*; Maruyama, Toshiki; Tatsumi, Toshitaka*
Nuclear Physics A, 906, p.37 - 49, 2013/05
Times Cited Count：11 Percentile：33.76(Physics, Nuclear)Inside neutron stars, the hadron-quark mixed phase is expected during the first order phase transition from the hadron phase to the quark phase. The geometrical structure of the mixed phase strongly depends on the surface tension at the hadron-quark interface. We evaluate the shear modulus which is one of the specific properties of the hadron-quark mixed phase. As an application, we study shear oscillations due to the hadron-quark mixed phase in neutron stars. We find that the frequencies of shear oscillations depend strongly on the surface tension; with a fixed stellar mass, the fundamental frequencies are almost proportional to the surface tension. Thus, one can estimate the value of surface tension via the observation of stellar oscillations with the help of the information on the stellar mass.
Noda, Tsuneo*; Hashimoto, Masaaki*; Yasutake, Nobutoshi*; Maruyama, Toshiki; Tatsumi, Toshitaka*; Fujimoto, Masayuki*
Astrophysical Journal, 765(1), p.1_1 - 1_5, 2013/03
Times Cited Count：22 Percentile：37.02(Astronomy & Astrophysics)Yasutake, Nobutoshi*; Noda, Tsuneo*; Sotani, Hajime*; Maruyama, Toshiki; Tatsumi, Toshitaka*
Recent Advances in Quarks Research, p.63 - 111, 2013/01
Yasutake, Nobutoshi*; Maruyama, Toshiki; Tatsumi, Toshitaka*
Physical Review D, 86(10), p.101302_1 - 101302_4, 2012/11
Times Cited Count：9 Percentile：59.58(Astronomy & Astrophysics)We have studied hadron-quark mixed phase in protoneutron stars, which is a ternary system, i.e., conserves the total baryon number, total charge, and total lepton number. We found that no crystalline "pasta" structure appears in the regime of high lepton number fraction; the size of pasta structure diverges due to the charge screening and the system becomes mechanically unstable. Consequently the whole system is separated into two bulk regions like an amorphous state, where the surface effect is safely neglected. There, the local charge neutrality is approximately attained, so that the equation of state is effectively reduced to that of a binary system. However, since the lepton-number fraction as well as baryon-number density is different for two phases in the amorphous state, we cannot reduce it to a pure system. Hence, we conclude that there is no possibility of a density discontinuity, which is a specific feature in a pure system, to appear in protoneutron-star matter.
Okamoto, Minoru; Maruyama, Toshiki; Yabana, Kazuhiro*; Tatsumi, Toshitaka*
Proceedings of Science (Internet), 6 Pages, 2012/11
In low-density nuclear matter which is relevant to neutron star crust, non-uniform structures called "nuclear pasta" are expected. In most of the previous studies, the crystalline of "nuclear pasta" and uniform background electron are assumed and/or the Wigner-Seitz (WS) cell approximation is used. For matter with droplets, body-centered cubic (bcc) lattice is found to be more favored than face-centered cubic (fcc) and simple cubic. This conclusion has been obtained by comparing the Coulomb energy with a fixed size of droplets. To be more precise, we should take into account the effect of non-uniformity of electron and optimal sizes of the droplets. We perform numerical calculations of non-uniform nuclear matter based on the relativistic mean field theory and Thomas-Fermi model with fully three-dimensional geometry. The most stable structure and the equation of state of matter with and without WS cell approximation and the energy difference between fcc and bcc for droplet are compared.
Maruyama, Toshiki; Yasutake, Nobutoshi*; Tatsumi, Toshitaka*
Proceedings of Science (Internet), 6 Pages, 2012/11
We explore the inhomogeneous structures and properties of nuclear matter with inclusion of trapped neutrinos which is relevant to the supernovae and the crust of proto-neutron stars. As a theoretical framework we employ the relativistic mean field (RMF) model with the Thomas-Fermi approximation for fermions. In our previous studies of nuclear matter without neutrino, we have observed "pasta" structures in nuclear matter with a fixed electron fraction while there appeared only spherical nuclei in catalyzed nuclear matter. In our present study of catalyzed nuclear matter with a fixed lepton fraction, pasta structures are found to be persistent due to the increase of protonfraction which causes the formation of cluster of protons and neutrons by their strong attraction. We present the equation of state (EOS) of neutrino-trapped nuclear matter and discuss the effects of the existence of neutrinos.
Watanabe, Gentaro*; Maruyama, Toshiki
Neutron Star Crust, p.23 - 44, 2012/10
In supernova cores and neutron star crusts, nuclei with exotic shapes such as rod-like and slab-like nuclei are expected to exist. These nuclei are collectively called nuclear "pasta". For the past decades, existence of the pasta phases in the equilibrium state has been studied using various methods. Recently, the formation process of the pasta phases, which has been a long-standing problem, has been unveiled using molecular dynamics simulations. In this review, we first provide the astrophysical background of supernovae and neutron stars and overview the history of the study of the pasta phases. We then focus on the recent study on the formation process of the pasta phases. Finally, we discuss future important issues related to the pasta phases: their astrophysical evidence and consequences.
Tatsumi, Toshitaka*; Yasutake, Nobutoshi*; Maruyama, Toshiki
Neutron Stars; The Aspect of High Density Matter, Equations of State and Observables, p.199 - 231, 2012/10
We consider the first-order phase transitions and the phase equilibrium on the basis of the gibbs conditions, taking the liquid-gas phase transition in asymmetric nuclear matter as an example. Characteristic features of the mixed phase are figured out by solving the coupled equations for mean-fields and densities of constituent particles self-consistently. The mixed phase is inhomogeneous matter composed of two phases with characteristic shapes called "pasta". We take into account the coulomb interaction and the interface energy, and thereby sometimes we see the mechanical instability of the mixed phase. Thermal effect on the liquid-gas phase transition is also elucidated. Similarly hadron-quark deconfinement transition is studied in hyperonic matter, where the neutrino-trapping effect as well as the thermal effect is discussed. Specific features of the mixed phase are elucidated and the equation of state is presented.
