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Search Results: 1 - 10 of 839 matches for " Tsuyoshi Miyatsu "
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Neutron Star Properties in the Chiral Quark-Meson Coupling Model
Tsuyoshi Miyatsu,Koichi Saito
Physics , 2012, DOI: 10.1007/s00601-012-0567-z
Abstract: We study the properties of neutron star using the chiral quark-meson coupling model, in which the quark-quark hyperfine interaction due to the exchanges of gluon and pion based on chiral symmetry is considered. We also examine the effects of hyperons and $\Delta$-isobars in a neutron star. Extending the SU(6) spin-flavor symmetry to more general SU(3) flavor symmetry in the vector-meson couplings to baryons, the maximum mass of neutron star can reach the recently observed, massive pulsar mass, $1.97 \pm 0.04 M_{\odot}$. In this calculation, $\Lambda$ and $\Xi$ are generated in a neutron star, while $\Sigma$ and $\Delta$-isobars do not appear.
Effects of Fock term, tensor coupling and baryon structure variation on a neutron star
Tsuyoshi Miyatsu,Tetsuya Katayama,Koichi Saito
Physics , 2011, DOI: 10.1016/j.physletb.2012.02.009
Abstract: The equation of state for neutron matter is calculated within relativistic Hartree-Fock approximation. The tensor couplings of vector mesons to baryons are included, and the change of baryon internal structure in matter is also considered using the quark-meson coupling model. We obtain the maximum neutron-star mass of $\sim 2.0 M_\odot$, which is consistent with the recently observed, precise mass, $1.97\pm0.04 M_{\odot}$. The Fock contribution is very important and, in particular, the inclusion of tensor coupling is vital to obtain such large mass. The baryon structure variation in matter also enhances the mass of a neutron star.
EoS for massive neutron stars
Tetsuya Katayama,Tsuyoshi Miyatsu,Koichi Saito
Physics , 2012, DOI: 10.1088/0067-0049/203/2/22
Abstract: Using relativistic Hartree-Fock approximation, we investigate the properties of the neutron-star matter in detail. In the present calculation, we consider not only the tensor coupling of vector mesons to octet baryons and the form factors at interaction vertexes but also the internal (quark) structure change of baryons in dense matter. The relativistic Hartree-Fock calculations are performed in two ways: one is the calculation with the coupling constants determined by SU(6) (quark model) symmetry, the other is with the coupling constants based on SU(3) (flavor) symmetry. For the latter case, we use the latest Nijmegen (ESC08) model. Then, it is very remarkable that the particle composition of the core matter in SU(3) symmetry is completely different from that in SU(6) symmetry. In SU(6) symmetry, all octet baryons appear in the density region below $\sim 1.2$ fm$^{-3}$, while, in the ESC08 model, only the \Xi^- hyperon is produced. Furthermore, the medium modification of the internal baryon structure hardens the equation of state for the core matter. Taking all these effects into account, we can obtain the maximum neutron-star mass which is consistent with the recently observed mass, 1.97 \pm 0.04 M_\sun (PSR J1614-2230). We therefore conclude that the extension from SU(6) symmetry to SU(3) symmetry in the meson-baryon couplings and the internal baryon-structure variation in matter certainly enhance the mass of neutron star. Furthermore, the effects of the form factor at vertex and the Fock contribution including the tensor coupling due to the vector mesons are indispensable to describe the core matter. In particular, the Fock term is very vital in reproducing the preferable value of symmetry energy, a_4 (\simeq 30 - 40 MeV), in nuclear matter.
A new equation of state for neutron star matter with nuclei in the crust and hyperons in the core
Tsuyoshi Miyatsu,Sachiko Yamamuro,Ken'ichiro Nakazato
Physics , 2013, DOI: 10.1088/0004-637X/777/1/4
Abstract: The equation of state for neutron stars in a wide-density range at zero temperature is constructed. The chiral quark-meson coupling model within relativistic Hartree-Fock approximation is adopted for uniform nuclear matter. The coupling constants are determined so as to reproduce the experimental data of atomic nuclei and hypernuclei. In the crust region, nuclei are taken into account within the Thomas-Fermi calculation. All octet baryons are considered in the core region, while only $\Xi^{-}$ appears in neutron stars. The resultant maximum mass of neutron stars is $1.95M_\odot$, which is consistent with the constraint from the recently observed massive pulsar, PSR J1614-2230.
Equation of state for neutron stars in SU(3) flavor symmetry
Miyatsu, Tsuyoshi;Cheoun, Myung-Ki;Saito, Koichi
High Energy Physics - Phenomenology , 2013,
Abstract: Using several relativistic mean field models (such as GM1, GM3, NL3, TM1, FSUGold and IU-FSU) as well as the quark-meson coupling model, we calculate the particle fractions, the equation of state, the maximum mass and radius of a neutron star within relativistic Hartree approximation. In determining the couplings of the isoscalar, vector mesons to the octet baryons, we examine the extension of SU(6) spin-flavor symmetry to SU(3) flavor symmetry. Furthermore, we consider the strange ($\sigma^{\ast}$ and $\phi$) mesons, and study how they affect the equation of state. We find that the equation of state in SU(3) symmetry can sustain a neutron star with mass of $(1.8 \sim 2.1) M_{\odot}$ even if hyperons exist inside the core. In addition, the strange vector ($\phi$) meson and the variation of baryon structure in matter also play important roles in supporting a massive neutron star.
Equation of state for neutron stars with hyperons and quarks in relativistic Hartree-Fock approximation
Tsuyoshi Miyatsu,Myung-Ki Cheoun,Koichi Saito
Physics , 2015, DOI: 10.1088/0004-637X/813/2/135
Abstract: We construct the equation of state (EoS) for neutron stars explicitly including hyperons and quarks. Using the quark-meson coupling model with relativistic Hartree-Fock approximation, the EoS for hadronic matter is derived by taking into account the strange ($\sigma^{\ast}$ and $\phi$) mesons as well as the light non-strange ($\sigma$, $\omega$, $\vec{\pi}$ and $\vec{\rho}$) mesons. Relevant coupling constants are determined to reproduce the experimental data of nuclear matter and hypernuclei in SU(3) flavor symmetry. For quark matter, we employ the MIT bag model with one-gluon-exchange interaction, and Gibbs criteria for chemical equilibrium in the phase transition from hadrons to quarks. We find that the strange vector ($\phi$) meson and the Fock contribution make the hadronic EoS stiff, and that the maximum mass of a neutron star can be consistent with the observed mass of heavy neutron stars even if the coexistence of hadrons and quarks takes place in the core. However, in the present calculation the transition to pure quark matter does not occur in stable neutron stars. Furthermore, the lower bound of the critical chemical potential of the quark-hadron transition at zero temperature turns out to be around 1.5 GeV in order to be consistent with the recent observed neutron star data.
Equation of state for neutron stars in SU(3) flavor symmetry
Tsuyoshi Miyatsu,Myung-Ki Cheoun,Koichi Saito
Physics , 2013, DOI: 10.1103/PhysRevC.88.015802
Abstract: Using several relativistic mean field models (such as GM1, GM3, NL3, TM1, FSUGold and IU-FSU) as well as the quark-meson coupling model, we calculate the particle fractions, the equation of state, the maximum mass and radius of a neutron star within relativistic Hartree approximation. In determining the couplings of the isoscalar, vector mesons to the octet baryons, we examine the extension of SU(6) spin-flavor symmetry to SU(3) flavor symmetry. Furthermore, we consider the strange ($\sigma^{\ast}$ and $\phi$) mesons, and study how they affect the equation of state. We find that the equation of state in SU(3) symmetry can sustain a neutron star with mass of $(1.8 \sim 2.1) M_{\odot}$ even if hyperons exist inside the core. In addition, the strange vector ($\phi$) meson and the variation of baryon structure in matter also play important roles in supporting a massive neutron star.
Equation of state for neutron stars: Hyperon mixing in SU(3) flavor symmetry
Tsuyoshi Miyatsu,Myung-Ki Cheoun,Koichi Saito
Physics , 2014, DOI: 10.7566/JPSCP.1.013080
Abstract: Using various kinds of relativistic mean-field models as well as the quark-meson coupling model, we study in detail the properties of neutron stars. We find that the equation of state in SU(3) flavor symmetry can support a neutron star with mass of $(1.8 \sim 2.1) M_{\odot}$ even if hyperons exist inside the core of a neutron star.
Hyperons in nuclear matter
T. Miyatsu,K. Saito
Physics , 2009, DOI: 10.1143/PTP.122.1035
Abstract: The chiral version of the QMC model, in which the effect of gluon and pion exchanges is included self-consistently, is applied to the hyperons in a nuclear medium. The hyperfine interaction due to the gluon exchange plays an important role in the in-medium baryon spectra, while the pion-cloud effect is relatively small. At the quark mean-field level, the $\Lambda$ feels more attractive force than the \Sigma or \Xi in matter.
Minocycline for Schizophrenia: A critical review  [PDF]
Tsuyoshi Miyaoka
Open Journal of Psychiatry (OJPsych) , 2012, DOI: 10.4236/ojpsych.2012.224056
Abstract: Minocycline, an antibiotic of the tetracycline family, has been shown to display neurorestoractive or neuroprotective properties in various models of neurodegenerative diseases. In particular, it has been shown to delay motor alterations, inflammation and apoptosis in models of Huntington’s disease, amyotrophic lateral sclerosis and Parkinson’s disease. Despite controversies about its efficacy, the relative safety and tolerability of minocycline have led to the launching of various clinical trials. Previously, we reported the antipsychotic effects of minocycline in patients with schizophrenia. In a pilot investigation, we administered minocycline as an open-label adjunct to antipsychotic medication to patients with schizophrenia. The results of this trial suggested that minocycline might be a safe and effective adjunct to antipsychotic medications, and that augmentation with minocycline may prove to be a viable strategy for “boosting” antipsychotic efficacy and for treating schizophrenia. Recently, in randomized double-blind placebo-controlled clinical trials, the addition of minocycline to treatment as usual early in the course of schizophrenia predominantly improves negative symptoms. The present review summarizes the available data supporting the clinical testing of minocycline for patients with schizophrenia. In addition, we extend our discussion to the potential applications of minocycline for combining this treatment with cellular and molecular therapy.
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