Searcharxiv⌕ Search

arXiv subjects

Masayuki Matsuzaki

Publications and source records attributed to Masayuki Matsuzaki.

At least 37 records · Page 2Linked to original sources
arXiv2008

Tilting instability in negative-γrotating nuclei

Based on the cranking model and the random phase approximation, we point out that the wobbling excitation on top of the s band in ^{182}Os is stable against angular momentum tilting. This is consistent with the general trend that the wobbling excitations in γ<0 rotating nuclei are more stable than those in γ>0 ones found in our previous studies. In higher N isotopes known to be γsoft, however, a different type of tilting instability is expected. Its possible correspondence to the experimental data is also discussed.

nucl-th↗
arXiv2008

Critical endpoint in the Polyakov-loop extended NJL model

The critical endpoint (CEP) and the phase structure are studied in the Polyakov-loop extended Nambu--Jona-Lasinio model in which the scalar type eight-quark (σ^4) interaction and the vector type four-quark interaction are newly added. The σ^4 interaction largely shifts the CEP toward higher temperature and lower chemical potential, while the vector type interaction does oppositely. At zero chemical potential, the σ^4 interaction moves the pseudo-critical temperature of the chiral phase transition to the vicinity of that of the deconfinement phase transition.

hep-ph↗
arXiv2007

Parametrizations of triaxial deformation and E2 transitions of the wobbling band

By the very definition the triaxial deformation parameter $γ$ is related to the expectation values of the K=0 and K=2 components of the intrinsic quadrupole tensor operator. On the other hand, using the same symbol "$γ$", various different parametrizations of triaxial deformation have been employed, which are suitable for various types of the mean-field potentials. It is pointed out that the values of various "$γ$" are quite different for the same actual triaxial deformation, especially for the large deformation; for example, the difference can be almost a factor two for the case of the triaxial superdeformed bands recently observed in the Hf and Lu nuclei. In our previous work, we have studied the wobbling band in Lu nuclei by using the microscopic framework of the cranked Nilsson mean-field and the random phase approximation, where the most serious problem is that the calculated B(E2) value is about factor two smaller. It is shown that the origin of this underestimation can be mainly attributed to the small triaxial deformation; if is used the same triaxial deformation as in the analysis of the particle-rotor model, the calculated B(E2) increases and gives correct magnitude compared with the experimental data.

nucl-th↗
arXiv2007

Meson loop effect on high density chiral phase transition

We test the stability of the mean-field solution in the Nambu--Jona-Lasinio model. For stable solutions with respect to both the σand πdirections, we investigate effects of the mesonic loop corrections of 1/N_c, which correspond to the next-to-leading order in the 1/N_c expansion, on the high density chiral phase transition. The corrections weaken the first order phase transition and shift the critical chemical potential to a lower value. At N_c=3, however, instability of the mean field effective potential prevents us from determining the minimum of the corrected one.

hep-ph↗
arXiv2007

Effects of a multi-quark interaction on color superconducting phase transition in an extended NJL model

We study the interplay of the chiral and the color superconducting phase transitions in an extended Nambu--Jona-Lasinio model with a multi-quark interaction that produces the nonlinear chiral-diquark coupling. We observe that this nonlinear coupling adds up coherently with the ω^2 interaction to produce the chiral-color superconductivity coexistence phase or cancel each other depending on its sign. We discuss that large coexistence region in the phase diagram is consistent with the quark-diquark picture for the nucleon whereas its smallness is the prerequisite for the applicability of the Ginzburg-Landau approach.

hep-ph↗
arXiv2007

Structure of Strange Dwarfs with Color Superconducting Core

We study effects of two-flavor color superconductivity on the structure of strange dwarfs, which are stellar objects with similar masses and radii with ordinary white dwarfs but stabilized by the strange quark matter core. We find that unpaired quark matter is a good approximation to the core of strange dwarfs.

astro-ph↗
arXiv2006

Wobbling motion in triaxial superdeformed nuclei

We discuss some characteristic features of the wobbling motion excited on the triaxial superdeformed Lu nucleus. We show how these features are connected to the moments of inertia microscopically calculated by means of the quasiparticle RPA in the rotating frame.

nucl-th↗
arXiv2006

Chiral phase transition in an extended NJL model with higher-order multi-quark interactions

The chiral phase transition is studied in an extended Nambu--Jona-Lasinio model with eight-quark interactions. Equations for scalar and vector quark densities, derived in the mean field approximation, are nonlinear and mutually coupled. The scalar-type nonlinear term hastens the restoration of chiral symmetry, while the scalar-vector mixing term makes the transition sharper. The scalar-type nonlinear term shifts the critical endpoint toward the values predicted by lattice QCD simulations and the QCD-like theory.

nucl-th↗
arXiv2006

Liquid-gas instability and superfluidity in nuclear matter

We study effects of the medium polarization on superfluidity in symmetric nuclear matter in a relativistic formalism. An effect of the liquid-gas instability is emphasized. We examine two types of decomposition of the nucleon propagator; the standard Feynman-density and the particle-hole-antiparticle ones. In both cases, the medium polarization effect is determined by a characteristic cancellation among the σ, the longitudinal ω, and the σ-ωmixed polarizations. The instability leads to increase of pairing gap. Around the saturation density that is free from the instability the medium polarization enhances pairing gap in the former case whereas reduces in the latter. At the lowest density that is also free from the instability the gap increases in both cases.

nucl-th↗
arXiv2006

Ordered bicontinuous double-diamond morphology in subsaturation nuclear matter

We propose to identify the new "intermediate" morphology in subsaturation nuclear matter observed in a recent quantum molecular dynamics simulation with the ordered bicontinuous double-diamond structure known in block copolymers. We estimate its energy density by incorporating the normalized area-volume relation given in a literature into the nuclear liquid drop model. The resulting energy density is higher than the other five known morphologies.

nucl-th↗
arXiv2005

Precession Mode on High-K Configurations: Non-Collective Axially-Symmetric Limit of Wobbling Motion

We have studied the precession mode, the rotational excitation built on the high-$K$ isomeric state, in comparison with the recently identified wobbling mode. The random-phase-approximation (RPA) formalism, which has been developed for the nuclear wobbling motion, is invoked and the precession phonon is obtained by the non-collective axially-symmetric limit of the formalism. The excitation energies and the electromagnetic properties of the precession bands in $^{178}$W are calculated, and it is found that the results of RPA calculations well correspond to those of the rotor model; the correspondence can be understood by an adiabatic approximation to the RPA phonon. As a by-product, it is also found that the problem of too small out-of-band $B(E2)$ in our previous RPA wobbling calculations can be solved by a suitable choice of the triaxial deformation which corresponds to the one used in the rotor model.

nucl-th↗
arXiv2004

High-K Precession modes: Axially symmetric limit of wobbling motion

The rotational band built on the high-K multi-quasiparticle state can be interpreted as a multi-phonon band of the precession mode, which represents the precessional rotation about the axis perpendicular to the direction of the intrinsic angular momentum. By using the axially symmetric limit of the random-phase-approximation (RPA) formalism developed for the nuclear wobbling motion, we study the properties of the precession modes in $^{178}$W; the excitation energies, B(E2) and B(M1) values. We show that the excitations of such a specific type of rotation can be well described by the RPA formalism, which gives a new insight to understand the wobbling motion in the triaxial superdeformed nuclei from a microscopic view point.

nucl-th↗
arXiv2004

^{1}S_{0} proton superfluidity in neutron star matter: Impact of bulk properties

We study the ^{1}S_{0} proton pairing gap in neutron star matter putting emphasis on influence of the Dirac effective mass and the proton fraction on the gap within the relativistic Hartree-Bogoliubov model. The gap equation is solved using the Bonn-B potential as a particle-particle channel interaction. It is found that the maximal pairing gap Δ_{max} is 1-2 MeV, which has a strong correlation with the Dirac effective mass. Hence we suggest that it serves as a guide to narrow down parameter sets of the relativistic effective field theory. Furthermore, the more slowly protons increase with density in the core region of neutron stars, the wider the superfluid range and the slightly lower the peak of the gap become.

nucl-th↗
arXiv2004

Dynamical moments of inertia associated with wobbling motion in the triaxial superdeformed nucleus

The three moments of inertia associated with the wobbling mode built on the triaxial superdeformed states in Lu--Hf region are investigated by means of the cranked shell model plus random-phase approximation to the configurations with aligned quasiparticle(s). The result indicates that it is crucial to take into account the direct contribution to the moments of inertia from the aligned quasiparticle(s) so as to realize \mathcal{J}_x > \mathcal{J}_y in positive-γshapes.

nucl-th↗
arXiv2004

Instability of nuclear wobbling motion and tilted axis rotation

We study a possible correspondence between the softening of the wobbling mode and the "phase transition" of the one-dimensionally rotating mean field to a three-dimensionally rotating one by comparing the properties of the wobbling mode obtained by the one-dimensional cranking model + random phase approximation with the total routhian surface obtained by the three-dimensional tilted-axis cranking model. The potential surface for the observed wobbling mode excited on the triaxial superdeformed states in $^{163}$Lu is also analyzed.

nucl-th↗
arXiv2004

Microscopic Study of Wobbling Motions in Hf and Lu Nuclei

One of the most striking findings in the recent high-spin spectroscopy is the discovery of one-phonon, and possibly double-phonon, excitation of the nuclear wobbling rotational bands. In this talk, we first review the properties of observed wobbling motions, and discuss the failure and success of the possible interpretation in terms of the simple rotor model. Then, we further present results of our microscopic study in Hf and Lu nuclei by means of the theoretical framework, the cranked mean-field and the random phase approximation.

nucl-th↗
arXiv2004

Nuclear moments of inertia and wobbling motions in triaxial superdeformed nuclei

The wobbling motion excited on triaxial superdeformed nuclei is studied in terms of the cranked shell model plus random phase approximation. Firstly, by calculating at a low rotational frequency the γ-dependence of the three moments of inertia associated with the wobbling motion, the mechanism of the appearance of the wobbling motion in positive-γnuclei is clarified theoretically -- the rotational alignment of the πi_{13/2} quasiparticle(s) is the essential condition. This indicates that the wobbling motion is a collective motion that is sensitive to the single-particle alignment. Secondly, we prove that the observed unexpected rotational-frequency dependence of the wobbling frequency is an outcome of the rotational-frequency dependent dynamical moments of inertia.

nucl-th↗