arXiv subjects

Masanobu Yahiro

Publications and source records attributed to Masanobu Yahiro.

At least 127 records · Page 7Linked to original sources

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↗

arXiv2006

Quark propagators at finite temperature with the clover action

We study properties of the finite temperature quark propagator by using the SU(3) quenched lattice simulation in the Landau gauge and report numerical results of the standard Wilson quark case as well as the improved clover one. The mass function in the deconfinement phase is different from that of the confinement phase, especially at low momentum regions.

hep-lat↗

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

Holographic Model at Finite Temperature with $R$-chrage density

We consider a holographic model of QCD at finite temperature with nonzero chemical potentials conjugate to $R$-charge densities. A critical surface of the confinement-deconfinement phase transition is shown for five-dimensional charged black hole solution given by Behrnd, Cvetič and Sabra. On a special section of the parameter space, we find an critical curve being similar to the one expected in QCD. We calculate meson spectra and decay constants in the confinement phase of this section to see their temperature and chemical potential dependences. We could assure generalized GellMann-Oakes-Renner relation and the reduction of pion velocity near the critical point.

hep-ph↗

arXiv2005

Holographic Model for Mesons at Finite Temperature

A holographic model of QCD at finite temperature is proposed and thermal properties for light mesons are examined in terms of this model. We find interesting temperature dependences of masses and decay constants for several mesons, and Nambu-Goldstone theorem for the chiral symmetry breaking and generalized Gell-Mann-Oakes-Renner relation are assured at finite temperature. Furthermore, we can see in the chiral limit that the speed of the pion in the thermal medium decreases to zero when the temperature approaches to the critical point of quark confinement and deconfinement transition, where the chiral symmetry is restored.

hep-ph↗

arXiv2005

Holographic Model for Hadrons in Deformed AdS5 Background

Several physical quantities of light hadrons are examined by a new holographic model of QCD, which is the modified version of the one proposed by Erlich et al. defined on AdS${}_5$. In our model, AdS${}_5$ is deformed by a non-trivial bulk scalar, this is corresponding to adding the mass term of the adjoint fermions to the 4d SYM theory dual to the gravity on AdS${}_5$. We find that this deformation should be taken to be rather small, but its important effects are also seen.

hep-ph↗

arXiv2005

Flavor quark at high temperature from a holographic model

Gauge theory with light flavor quark is studied by embedding a D7 brane in a deconfinement phase background newly constructed. We find a phase transition by observing a jump of the vacuum expectation value of quark bilinear and also of the derivative of D7 energy at a critical temperature. For the model considered here, we also study quark-antiquark potential to see some possible quark-bound states and other physical quantities in the deconfinement phase.

hep-th↗

arXiv2004

Chiral symmetry breaking driven by dilaton

Dynamical properties of gauge theories with light flavor quarks are studied in a dual supergravity by adding a D7-brane probe into the AdS background deformed by the dilaton. By estimating the vev of flavor quark-bilinear in both the supersymmetric and non-supersymmetric gravity duals, we find spontaneous chiral symmetry breaking in the case of the non-supersymmetric background. We also study quark-antiquark potential for light quarks to see the quark confinement in the models considered here.

hep-th↗

arXiv2004

Radius stabilization and brane running in RS1 model

We study the effective potential of a scalar field based on the 5D gauged supergravity for the RS1 brane model in terms of the brane running method. The scalar couples to the brane such that the BPS conditions are satisfied for the bulk configuration. The resulting effective potential implies that the interbrane distance is undetermined in this case, and we need a small BPS breaking term on the brane to stabilize the interbrane distance at a finite length. We also discuss the relationship to the Goldberger-Wise model.

hep-th↗

arXiv2003

Effective action and brane running

We address the renormalized effective action for a Randall-Sundrum brane running in 5d bulk space. The running behavior of the brane action is obtained by shifting the brane-position without changing the background and the fluctuations. After an appropriate renormalization, we obtain an effective, low energy braneworld action, in which the effective 4d Planck mass is independent of the running-position. We address some implications of this effective action.

hep-th↗

arXiv2003

Newton's law in de Sitter brane

Newton potential has been evaluated for the case of dS brane embedded in Minkowski, dS$_5$ and AdS$_5$ bulks. We point out that only the AdS$_5$ bulk might be consistent with the Newton's law from the brane-world viewpoint when we respect a small cosmological constant observed at present universe.

hep-th↗

arXiv2003

Instability of thick brane worlds

We examined 5d thick brane worlds constructed by a real scalar field. The solutions are obtained in terms of a simple form of smooth warp factor. For the case of dS brane, we found a disease of the solutions. For example, it is impossible to construct thick-brane worlds with our simple smoothing. This result is independent of supersymmetry or other symmetries.

hep-th↗

arXiv2003

Scalar field localization on a brane with cosmological constant

We address the localization of a scalar field, whose bulk-mass M is considered in a wide range including the tachyonic region,on a three-brane. The brane with non-zero cosmological constant $λ$ is embedded in five dimensional bulk space. We find in this case that the trapped scalar could have mass $m$ which has an upper bound and expressed as $m^2=m_0^2+αM^2\leq β|λ|$ with the calculable numbers $m_0^2, α, β$. We point out that this result would be important to study the stability of the brane and cosmological problems based on the brane-world.

hep-th↗

arXiv2002

Origin of Small Cosmological Constant in Brane-World

We address the relation among the parameters of accelerating brane-universe embedded in five dimensional bulk space. It is pointed out that the tiny cosmological constant of our world can be obtained as quantum corrections around a given brane-solution in the bulk theory or in the field theory on the boundary from the holographic viewpoint.Some implications to the cosmology and constarints on the parameters are also given.

hep-th↗

arXiv2002

Determination of S17 from 7Be(d,n)8B reaction: CDCC analyses based on three-body model

The astrophysical factor $S_{17}$ for $^7$Be($p,γ$)$^8$B reaction is reliably extracted from the transfer reaction $^7$Be($d,n$)$^8$B at $E=7.5$ MeV with the asymptotic normalization coefficient method. The transfer reaction is accurately analyzed with CDCC based on the three-body model. This analysis is free from uncertainties of the optical potentials having been crucial in the previous DWBA analyses.

nucl-th↗

arXiv2002

Localization of Gravity on Brane Embedded in $AdS_5$ and $dS_5$

We address the localization of gravity on the Friedmann-Robertson-Walker type brane embedded in either $AdS_{5}$ or $dS_{5}$ bulk space,and derive two definite limits between which the value of the bulk cosmological constant has to lie in order to localize the graviton on the brane.The lower limit implies that the brane should be either $dS_{4}$ or 4d Minkowski in the $AdS_{5}$ bulk.The positive upper limit indicates that the gravity can be trapped also on curved brane in the $dS_{5}$ bulk space.Some implications to recent cosmological scenarios are also discussed.

hep-th↗

arXiv1998

Critical coupling in (1+1)-dimensional light-front $ϕ^{4}$ theory

The spontaneous symmetry breaking in (1+1)-dimensional $ϕ^{4}$ theory is studied with discretized light-front quantization, that is, by solving the zero-mode constraint equation. The symmetric ordering is assumed for the operator-valued constraint equation. The commutation relation between the zero mode and each oscillator mode is calculated with $\hbar$ expansion. A critical coupling evaluated from the first some terms in the expansion is $28.8μ^{2}/\hbar \le λ_{cr} \le 31.1μ^{2}/\hbar$ consistent with the equal-time one $22μ^{2}/\hbar \le λ_{cr} \le 55.5μ^{2}/\hbar$. The same analysis is also made under another operator ordering.

hep-th↗

arXiv1996

Nonperturbative renormalization group in a light-front three-dimensional real scalar model

The three-dimensional real scalar model, in which the $Z_2$ symmetry spontaneously breaks, is renormalized in a nonperturbative manner based on the Tamm-Dancoff truncation of the Fock space. A critical line is calculated by diagonalizing the Hamiltonian regularized with basis functions. The marginal ($ϕ^6$) coupling dependence of the critical line is weak. In the broken phase the canonical Hamiltonian is tachyonic, so the field is shifted as $ϕ(x)\toφ(x)+v$. The shifted value $v$ is determined as a function of running mass and coupling so that the mass of the ground state vanishes.

hep-th↗