arXiv subjects

T. Muta

Publications and source records attributed to T. Muta.

13 recordsLinked to original sources

arXiv1999

Curvature-induced phase transitions in the inflationary universe - Supersymmetric Nambu-Jona-Lasinio Model in de Sitter spacetime -

The phase structure associated with the chiral symmetry is thoroughly investigated in de Sitter spacetime in the supersymmetric Nambu-Jona-Lasinio model with supersymmetry breaking terms. The argument is given in the three and four space-time dimensions in the leading order of the 1/N expansion and it is shown that the phase characteristics of the chiral symmetry is determined by the curvature of de Sitter spacetime. It is found that the symmetry breaking takes place as the first order as well as second order phase transition depending on the choice of the coupling constant and the parameter associated with the supersymmetry breaking term. The critical curves expressing the phase boundary are obtained. We also discuss the model in the context of the chaotic inflation scenario where topological defects (cosmic strings) develop during the inflation.

gr-qc↗

arXiv1999

Path-Integral Formulation of Casimir Effects in Supersymmetric Quantum Electrodynamics

The Casimir effect is an interesting phenomenon in the sense that it provides us with one of the primitive means of extracting the energy out of the vacuum. Since the original work of Casimir a number of works have appeared in extending the result to the case of more general topological and dynamical configurations of the boundary condition and to the circumstances at finite temperature and gravity. In the studies of the Casimir effects it is common to assume the free electromagnetic field in the bounded region. It may be interesting to extend our arguments for fields other than the electromagnetic field. The Casimir effect due to the free fermionic fields has been investigated by several authors and has been found to result in an attractive force under the suitable physical boundary conditions.

hep-ph↗

arXiv1999

Pattern of Chiral Symmetry Restoration at Finite Temperature in A Supersymmetric Composite Model

The structure of chiral symmetry restorations at finite temperature is thoroughly investigated in the supersymmetric Nambu-Jona-Lasinio model with a soft supersymmetry breaking term. It is found that the broken chiral symmetry at vanishing temperature is restored at sufficiently high temperature in two patterns, i. e., the first order and second order phase transition depending on the choice of the coupling constant $G$ and the supersymmetry breaking parameter $Δ$. The critical curves expressing the phase boundaries in the $G-Δ$ plane are completely determined and the dynamically generated fermion mass is calculated as a function of temperature.

hep-ph↗

arXiv1998

A Model of Curvature-Induced Phase Transitions in Inflationary Universe

Chiral phase transitions driven by space-time curvature effects are investigated in de Sitter space in the supersymmetric Nambu-Jona-Lasinio model with soft supersymmetry breaking. The model is considered to be suitable for the analysis of possible phase transitions in inflationary universe. It is found that a restoration of the broken chiral symmetry takes place in two patterns for increasing curvature : the first order and second order phase transition respectively depending on initial settings of the four-body interaction parameter and the soft supersymmetry breaking parameter. The critical curves expressing the phase boundaries in these parameters are obtained. Cosmological implications of the result are discussed in connection with bubble formations and the creation of cosmic strings during the inflationary era.

gr-qc↗

arXiv1998

Thermal Restoration of Chiral Symmetry in Supersymmetric Nambu-Jona-Lasinio Model with Soft SUSY Breaking

The supersymmetric version of the Nambu-Jona-Lasinio model is investigated in connection with the chiral symmetry breaking induced by a soft SUSY breaking term. It is found that the broken chiral symmetry due to the soft breaking term is restored at suitably high temperature and the symmetry restoration occurs as first-order phase transitions. The critical temperature at which the chiral symmetry is restored is determined as a function of the strength of the soft breaking term and the field coupling constant. The dynamical fermion mass is calculated at finite temperature. Some possible applications to the breaking scenario of unified field theories are discussed.

hep-ph↗

arXiv1997

Dynamical symmetry breaking in curved spacetime -review-

Four-fermion interaction models are considered to be prototype models for dynamical symmetry breaking.The present review deals with recent developments in the studies of dynamical symmetry breaking in the four-fermion interaction models and their extension in curved spacetime. Starting with the Minkowski spacetime in dimension $D$ ($2 \leq D \leq 4$) the effective potential in the leading order of $1/N$-expansion is calculated and the phase structure of the theory is investigated. In curved spacetime curvature-induced phase transitions are discussed in the circumstances where fermion masses are dynamically generated. Subsequently a possibility of curvature- and temperature-induced or curvature- and topology-induced phase transitions is discussed. It is also argued that the chiral symmetry broken by a weak magnetic field may be restored due to the presence of gravitational field. Finally some applications of four-fermion models in quantum gravity are briefly described.

hep-th↗

arXiv1997

Isgur-Wise Function for $Λ_b \to Λ_c$ in B-S Approach

In the heavy quark limit, the heavy baryon $Λ_Q$ (Q=b or c) can be regarded as composed of a heavy quark and a scalar light diquark which has good spin and flavor quantum numbers. Based on this picture we establish the Bethe-Salpeter (B-S) equation for $Λ_Q$ in the leading order of $1/m_Q$ expansion. With the kernel containing both the scalar confinement and one-gluon-exchange terms we solve the B-S equation numerically. The Isgur-Wise function for $Λ_b \to Λ_c$ is obtained numerically from our model. Comparison with other model calculations are also presented. It seems that the Isgur-Wise function for $Λ_b \to Λ_c$ drops faster than that for $B \to D$. The differential and total decay widths for $Λ_b \to Λ_c l \barν$ are given in the limit $m_{b,c}\to \infty$.

hep-ph↗

arXiv1995

Dynamical Symmetry Breaking in Einstein Universe

We investigate four-fermion interactions with $N$-component fermion in Einstein universe for arbitrary space-time dimensions ($2 \leq D<4$). It is found that the effective potential for composite operator $\overlineψψ$ is calculable in the leading order of the $1/N$ expansion. The resulting effective potential is analyzed by varying the curvature of the space-time and is found to exhibit the symmetry restoration through the second-order phase transition. The critical curvature at which the dynamical fermion mass disappears is analytically calculated.

hep-th↗

arXiv1995

Scalar and Spinor Two-Point Functions in Einstein Universe

Two-point functions for scalar and spinor fields are investigated in Einstein universe ($R \otimes S^{\sN-1}$). Equations for massive scalar and spinor two-point functions are solved and the explicit expressions for the two-point functions are given. The simpler expressions for massless cases are obtained both for the scalar and spinor cases.

hep-th↗

arXiv1995

A Soluble Model of Four-Fermion Interactions in de Sitter Space

We consider the theory of four-fermion interactions with N-component fermions in de Sitter space. It is found that the effective potential for a composite operator in the theory is calculable in the leading order of the 1/N expansion. The resulting effective potential is analyzed by varying both the four-fermion coupling constant and the curvature of the space-time. The critical curvature at which the dynamically generated fermion mass disappears is found to exist and is calculated analytically. The dynamical fermion mass is expressed as a function of the space-time curvature.

hep-th↗

arXiv1994

Phase Structure of Four-Fermion Theories at Finite Temperature and Chemical Potential in Arbitrary Dimensions

The phase structure of four-fermion theories is thoroughly investigated with varying temperature and chemical potential for arbitrary space-time dimensions $(2 \leq D < 4)$ by using the 1/N expansion method. It is shown that the chiral symmetry is restored in the theory under consideration for sufficiently high temperature and/or chemical potential. The critical line dividing the symmetric and broken phase is given explicitly. It is found that for space-time dimension $2 \leq D < 3$ both the first-order and second-order phase transition occur depending on the value of temperature and chemical potential while for $3 \leq D < 4$ only the second-order phase transition exists.

hep-ph↗

arXiv1993

Nambu-Jona-Lasinio Model in Curved Space-Time

The phase structure of Nambu-Jona-Lasinio model with N-component fermions in curved space-time is studied in the leading order of the 1/N expansion. The effective potential for composite operator $\barψψ$ is calculated by using the normal coordinate expansion in the Schwinger proper-time method. The existence of the first-order phase transition caused by the change of the space-time curvature is confirmed and the dynamical mass of the fermion is calculated as a simultaneous function of the curvature and the four-fermion coupling constant. The phase diagram in the curvature and the coupling constant is obtained.

hep-th↗

arXiv1992

Dynamical CP Violation in Composite Higgs Models

The dynamical origin of the CP violation in electroweak theory is investigated in composite Higgs models. The mechanism of the spontaneous CP violation proposed in other context by Dashen is adopted to construct simple models of the dynamical CP violation. Within the models the size of the neutron electric dipole moment is estimated and the constraint on the $\varepsilon$-parameter in K-meson decays is discussed.

hep-ph↗