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H. Kouno

Publications and source records attributed to H. Kouno.

14 recordsLinked to original sources
arXiv2008

Roberge-Weiss phase transitions and extended Z3 symmetry

Using the Polyakov extended Nambu-Jona-Lasinio (PNJL) model with imaginary chemical potential, the relation between the Roberge-Weiss (RW) phase transition and the extended Z3 symmetry is studied. At low temperature, there is approximate continuous symmetry under the phase transformation of the Polyakov loop with the shift of the imaginary chemical potential. Due to this continuous symmetry, the Polyakov loop can oscillate smoothly as the imaginary chemical potential increases. At high temperature, this continuous symmetry is broken to an exact discrete symmetry, the extended Z3 symmetry, and the Polyakov loop can not oscillate smoothly. This symmetry breaking of the continuous symmetry causes a discontinuity of the Polyakov loop. That is the RW phase transition.

hep-ph↗
arXiv2005

Auxiliary Field Meson Model at Finite Temperature and Density

Starting from many quark interactions, we construct a nonlinear sigma-omega model at finite temperature and density. The mesons are introduced as auxiliary fields. Effective quark-meson couplings are strongly related to effective meson masses, since they are derived simultaneously from the original many quark interactions. In this model, even if the effective omega-meson mass decreases due to the partial chiral restoration, the equation of state (EOS) of nuclear matter can become soft.

nucl-th↗
arXiv2005

Two-scale scalar mesons in nuclei

We generalize the linear sigma model in order to develop a chiral-invariant model of nuclear structure. The model is natural, and contains not only the usual sigma meson which is the chiral partner of the pion but also a new chiral-singlet that is responsible for the medium-range nucleon-nucleon attraction. This approach provides significant advantages in terms of its description of nuclear matter and finite nuclei in comparison with conventional models based on the linear sigma model.

nucl-th↗
arXiv2002

Proton Irradiation Experiment for the X-ray Charge-Coupled Devices of the Monitor of All-sky X-ray Image mission onboard the International Space Station: I. Experimental Setup and Measurement of the Charge Transfer Inefficiency

We have investigated the radiation damage effects on a CCD to be employed in the Japanese X-ray astronomy mission including the Monitor of All-sky X-ray Image (MAXI) onboard the International Space Station (ISS). Since low energy protons release their energy mainly at the charge transfer channel, resulting a decrease of the charge transfer efficiency, we thus focused on the low energy protons in our experiments. A 171 keV to 3.91 MeV proton beam was irradiated to a given device. We measured the degradation of the charge transfer inefficiency (CTI) as a function of incremental fluence. A 292 keV proton beam degraded the CTI most seriously. Taking into account the proton energy dependence of the CTI, we confirmed that the transfer channel has the lowest radiation tolerance. We have also developed the different device architectures to reduce the radiation damage in orbit. Among them, the ``notch'' CCD, in which the buried channel implant concentration is increased, resulting in a deeper potential well than outside, has three times higher radiation tolerance than that of the normal CCD. We then estimated the charge transfer inefficiency of the CCD in the orbit of ISS, considering the proton energy spectrum. The CTI value is estimated to be 1.1e-5 per each transfer after two years of mission life in the worse case analysis if the highest radiation-tolerant device is employed. This value is well within the acceptable limit and we have confirmed the high radiation-tolerance of CCDs for the MAXI mission.

physics.ins-det↗
arXiv2002

Application of the Mesh Experiment for the Back-Illuminated CCD: I. Experiment and the Charge Cloud Shape

We have employed a mesh experiment for back-illuminated (BI) CCDs. BI CCDs possess the same structure to those of FI CCDs. Since X-ray photons enter from the back surface of the CCD, a primary charge cloud is formed far from the electrodes. The primary charge cloud expands through diffusion process until it reaches the potential well that is just below the electrodes. Therefore, the diffusion time for the charge cloud produced is longer than that in the FI CCD, resulting a larger charge cloud shape expected. The mesh experiment enables us to specify the X-ray point of interaction with a subpixel resolution. We then have measured a charge cloud shape produced in the BI CCD. We found that there are two components of the charge cloud shape having different size: a narrow component and a broad component. The size of the narrow component is $2.8-5.7 μ$m in unit of a standard deviation and strongly depends on the attenuation length in Si of incident X-rays. The shorter the attenuation length of X-rays is, the larger the charge cloud becomes. This result is qualitatively consistent with a diffusion model inside the CCD. On the other hand, the size of the broad component is roughly constant of $\simeq 13 μ$m and does not depend on X-ray energies. Judging from the design value of the CCD and the fraction of each component, we conclude that the narrow component is originated in the depletion region whereas the broad component is in the field-free region.

physics.ins-det↗
arXiv2002

Direct X-ray Imaging of $μ$m precision using Back-Illuminated CCD

A charge-coupled device (CCD) is a standard imager in optical region in which the image quality is limited by its pixel size. CCDs also function in X-ray region but with substantial differences in performance. An optical photon generates only one electron while an X-ray photon generates many electrons at a time. We developed a method to precisely determine the X-ray point of interaction with subpixel resolution. In particular, we found that a back-illuminated CCD efficiently functions as a fine imager. We present here the validity of our method through an actual imaging experiment.

astro-ph↗
arXiv1999

Effective Vector Meson Masses in a Cutoff Field Theory

Based on quantum hadrodynamics with a finite cutoff, the effective masses of vector mesons(ω, ρ) in nuclear medium are calculated. We use a low-energy effective Lagrangian which is obtained by integrating high-energy quantum fluctuations. Although we use an artificial cutoff, the cutoff-dependence can be removed order by order. It is shown that there is a strong correlation between the effective ω-meson mass and the effective nucleon mass at the normal density. It is also found that the effective ρ-meson mass m_ρ^* decreases as density increases. The rate of the decrease becomes smaller at high density. As a result, at the normal density, the m^*_ρ/m_ρis 0.85 \sim 0.95.

nucl-th↗
arXiv1999

Dispersion relations in quantum hadrodynamics with a finite cutoff

The dispersion relations in the real and imaginary parts of the meson self-energies are studied to check the consistency of the "renormalization" in cutoff field theory. It is shown that the dispersion relations are preserved by the "renormalization"even if the finite cutoff and regulator are introduced in the calculation by hand.

nucl-th↗
arXiv1998

Antiproton Production in p+d Reaction at Subthreshold Energies

An enhancement of antiprotons produced in p+d reaction in comparison with ones in p+p elementary reaction is investigated. In the neighborhood of subthreshold energy the enhancement is caused by the difference of available energies for antiproton production. The cross section in p+d reaction, on the other hand, becomes just twice of the one in elementary p+p reaction at the incident energy far from the threshold energy when non-nucleonic components in deuteron target are not considered.

nucl-th↗
arXiv1996

Properties of nuclear matter in cut-off field theory and renormalization group methods

The properties of nuclear matter are studied in the cut-off field theory. It is found that, under the Hartree approximation, the small cut-off makes the equations of state hard, especially at higher densities. The theory is modified in the framework of the renormalization group methods with arbitrary cut-off $Λ^\prime$. It is found that the expansion in terms of the $σ$ meson field is more favorable than the naive expansion of the inverse of $Λ^\prime$, when we do not use very large $Λ^\prime$.

nucl-th↗
arXiv1995

Volume, Coulomb, and volume-symmetry coefficients of nucleus incompressibility in the relativistic mean field theory with the excluded volume effects

The relation among the volume coefficient $K$(=incompressibility of the nuclear matter), the Coulomb coefficient $K_c$, and the volume-symmetry coefficient $K_{vs}$ of the nucleus incompressibility are studied in the framework of the relativistic mean field theory with the excluded volume effects of the nucleons, under the assumption of the scaling model. It is found that $K= 300\pm 50$MeV is necessary to account for the empirical values of $K$, $K_c$, and $K_{vs}$, simultaneously, as is in the case of the point-like nucleons. The result is independent on the detail descriptions of the potential of the $σ$-meson self-interaction and is almost independent on the excluded volume of the nucleons.

nucl-th↗
arXiv1995

Compressional properties of nuclear matter in the relativistic mean field theory with the excluded volume effects

Compressional properties of nuclear matter are studied by using the mean field theory with the excluded volume effects of the nucleons. It is found that the excluded volume effects make it possible to fit the empirical data of the Coulomb coefficient $K_{c}$ of nucleus incompressibility, even if the volume coefficient $K$ is small($\sim 150$MeV). However, the symmetry properties favor $K=300\pm 50$MeV as in the cases of the mean field theory of point-like nucleons.

nucl-th↗
arXiv1995

Incompressibility of nuclear matter, and Coulomb and volume-symmetry coefficients of nucleus incompressibility in the relativistic mean field theory

The volume coefficient $K$(=incompressibility of the nuclear matter), the Coulomb coefficient $K_c$, and the volume-symmetry coefficient $K_{vs}$ of the nucleus incompressibility are studied in the framework of the relativistic mean field theory, with aid of the scaling model. It is found that $K= 300\pm 50$MeV is necessary to account for the empirical values of $K_v$, $K_c$, and $K_{vs}$, simultaneously. The result is independent on the detail descriptions of the potential of the $σ$-meson self-interaction and is almost independent of the strength of the $ω$-meson self-interaction.

nucl-th↗