arXiv subjects

Tomohiro Inagaki

Publications and source records attributed to Tomohiro Inagaki.

At least 55 records · Page 3Linked to original sources

arXiv2010

Curvature and topological effects on dynamical symmetry breaking in a four- and eight-fermion interaction model

A dynamical mechanism for symmetry breaking is investigated under the circumstances with the finite curvature, finite size and non-trivial topology. A four- and eight-fermion interaction model is considered as a prototype model which induces symmetry breaking at GUT era. Evaluating the effective potential in the leading order of the 1/N-expansion by using the dimensional regularization, we explicitly calculate the phase boundary which divides the symmetric and the broken phase in a weakly curved space-time and a flat space-time with non-trivial topology, $R^{D-1} \otimes S^1$.

hep-ph↗

arXiv2010

Topological and Curvature Effects in a Multi-fermion Interaction Model

A multi-fermion interaction model is investigated in a compact spacetime with non-trivial topology and in a weakly curved spacetime. Evaluating the effective potential in the leading order of the 1/N expansion, we show the phase boundary for a discrete chiral symmetry in an arbitrary dimensions, $2\leq D<4$.

hep-ph↗

arXiv2008

Four- and eight-fermion interactions in a space-time with non-trivial topology

The phase structure of an eight-fermion interaction model is investigated in a compact space-time with non-trivial topology, $M^{D-1}\otimes S^1$. The phase boundary dividing the symmetric and the broken phase is shown as a function of the space-time dimensions. It is found that the eight-fermion interaction does not modify the phase boundary for the chiral symmetry breaking.

hep-ph↗

arXiv2008

Multi-fermion interaction models in curved spacetime

A model with a scalar type eight-fermion interaction is investigated in curved spacetime. The ground state of the model can be obtained by observing the effective potential. Applying the Riemann normal coordinate expansion, we calculate an effective potential of the model in a weakly curved spacetime. The result is extended to models with multi-fermion interactions. We numerically show the behavior of the effective potential and find the phase structure of the model.

hep-ph↗

arXiv2007

Phase structure of NJL model with finite quark mass and QED correction

We study QED corrections to the chiral symmetry breaking in Nambu-Jona-Lasinio (NJL) model with two flavors of quarks. In the model the isospin symmetry is broken by differences of the current quark masses and the electromagnetic charges between up and down quarks. In the leading order of the 1/N expansion we calculate the effective potential of the model with one-loop QED corrections. Evaluating the effective potential, we study an influence of the isospin symmetry breaking on the orientation of chiral symmetry breaking. The current quark mass has an important contribution for the orientation of chiral symmetry breaking.

hep-ph↗

arXiv2006

Radiative Symmetry Breaking and Dynamical Origin of Cosmological Constant in $ϕ^4$ Theory with Non-Linear Curvature Coupling

A scalar self-interacting theory non-linearly coupled with some power of the curvature have a possibility to explain the current smallness of the cosmological constant. Here one concentrate on a massless scalar field in the four-dimensional Fridmann-Robertson-Walker (FRW) spacetime with flat spatial part. One show the phase structure of radiative symmetry breaking and review a dynamical resolution of the cosmological constant problem.

gr-qc↗

arXiv2004

Proper-Time Formalism in a Constant Magnetic Field at Finite Temperature and Chemical Potential

We investigate scalar and spinor field theories in a constant magnetic field at finite temperature and chemical potential. In an external constant magnetic field the exact solution of the two-point Green functions are obtained by using the Fock-Schwinger proper-time formalism. We extend it to the thermal field theory and find the expressions of the Green functions exactly for the temperature, the chemical potential and the magnetic field. For practical calculations the contour of the proper-time integral is carefully selected. The physical contour is discussed in a constant magnetic field at finite temperature and chemical potential. As an example, behavior of the vacuum self-energy is numerically evaluated for the free scalar and spinor fields.

hep-ph↗

arXiv2004

NJL Model at Finite Chemical Potential in a Constant Magnetic Field

We investigate the influence of an external magnetic field on chiral symmetry breaking in the Nambu-Jona-Lasinio (NJL) model at finite temperature and chemical potential. According to the Fock-Schwinger proper-time method, we calculate the effective potential in the leading order of the $1/N_c$ expansion. The phase boundary dividing the symmetric phase and the broken phase is illustrated numerically. A complex behavior of the phase boundary is found for large chemical potential.

hep-ph↗

arXiv2004

Four-fermion Interaction Model in a Constant Magnetic Field at Finite Temperature and Chemical Potential

We investigate an influence of an external magnetic field on chiral symmetry breaking in a four-fermion interaction model at finite temperature and chemical potential. By using the Fock-Schwinger proper-time method, we calculate the effective potential for the four-fermion interaction model at the leading order of the $1/N_c$ expansion. A phase structure of the chiral symmetry breaking is shown on $T$-$μ$, $H$-$T$ and $μ$-$H$ planes. The external magnetic field modifies the phase structure. It is found that a new phase appears for a large chemical potential.

hep-ph↗

arXiv2003

Dynamical Low-Mass Fermion Generation in Randall-Sundrum Background

It is investigated that a dynamical mechanism to generate a low mass fermion in Randall-Sundrum (RS) background. We consider a five-dimensional four- fermion interaction model with two kinds of bulk fermion fields and take all the mass scale in the five-dimensional spacetime at the Planck scale. Evaluating the effective potential of the induced four-dimensional model, I calculate the dynamically generated fermion mass. It is shown that dynamical symmetry breaking takes place and one of the fermion mass is generated at the electroweak scale in four dimensions.

hep-ph↗

arXiv2003

Dynamical Symmetry Breaking in Randall-Sundrum Background

Characteristic features of dynamical symmetry breaking are investigated in Randall-Sundrum (RS) background. To study the influence of bulk fermion or bulk gauge field I consider a five-dimensional four-fermion interaction model and a non-Abelian gauge field theory as simple models where the chiral symmetry is broken down dynamically. Using a four-dimensional Lagrangian induced from the five-dimensional theory, I calculate the dynamically generated fermion mass and show how the extra dimension affects the chiral phase transition in the RS background.

hep-ph↗

arXiv2003

Dynamical origin of low-mass fermions in Randall-Sundrum background

We investigate a dynamical mechanism to generate fermion mass in the Randall-Sundrum background. We consider four-fermion interaction models where the fermion field propagates in an extra-dimension, i.e. the bulk four-fermion interaction model. It is assumed that two types of fermions with opposite parity exist in the bulk. We show that electroweak-scale mass is dynamically generated for a specific fermion anti-fermion condensation, even if all the scale parameters in the Lagrangian are set to the Planck scale.

hep-ph↗

arXiv2003

Dark Energy Problem in a Four-Fermion Interaction Model

Cosmology enters precision testing period with the observational experiments advancement. We have not arrived to decipher the origin of the dominant dark energy component of our universe, although we have located some of its characters. In such a situation the possibilities of a simple four-fermion interaction model are investigated to describe dark energy characters. We explicitly calculate the vacuum expectation value of the energy-momentum tensor and discuss the results with comparison to the equation of state for dark energy requirement. It is found that the negative pressure is realized at low temperature. It is an appropriate property as a dark energy candidate. We also investigate some cosmological tests for the dark energy via its equation of state.

hep-ph↗

arXiv2002

Schwinger-Dyson Analysis of Dynamical Symmetry Breaking on a Brane with Bulk Yang-Mills Theory

The dynamically generated fermion mass is investigated in the flat brane world with (4+delta)-dimensional bulk space-time, and in the Randall-Sundrum (RS) brane world. We consider the bulk Yang-Mills theory interacting with the fermion confined on a four-dimensional brane. Based on the effective theory below the reduced cutoff scale on the brane, we formulate the Schwinger-Dyson equation of the brane fermion propagator. By using the improved ladder approximation we numerically solve the Schwinger-Dyson equation and find that the dynamical fermion mass is near the reduced cutoff scale on the brane for the flat brane world with delta >= 3 and for the RS brane world. In RS brane world KK excited modes of the bulk gauge field localized around the y = pi R brane and it enhances the dynamical symmetry breaking on the brane. The decay constant of the fermion and the anti-fermion composite operator can be taken to be the order of the electroweak scale much smaller than the Planck scale. Therefore electroweak mass scale can be realized from only the Planck scale in the RS brane world due to the fermion and the anti-fermion pair condensation. That is a dynamical realization of Randall-Sundrum model which solves the weak-Planck hierarchy problem.

hep-ph↗

arXiv2001

Chiral phase transition of bulk Abelian gauge theories in the Randall-Sundrum brane world

The chiral phase transition of strong-coupling Abelian gauge theories is investigated in the brane world. It is assumed that gauge boson propagates in an extra dimension, i.e. bulk gauge theories. The phase structure is analytically evaluated by using the low-energy effective theories. We also numerically solve the ladder Schwinger-Dyson equation for the full fermion propagator including Kaluza-Klein (KK) excitation modes of the gauge field. It is found that the chiral phase transition is of the second order, and the critical value of the coupling constant is obtained. The extra dimension has a large influence on the chiral phase transition for the Randall-Sundrum (RS) brane world. It is studied how the number of KK modes affect the chiral phase transition.

hep-ph↗

arXiv2001

Dynamical Fermion Masses Under the Influence of Kaluza-Klein Fermions in Randall-Sundrum Background

The dynamical fermion mass generation on the D3-brane in the Randall-Sundrum space-time is discussed in a model with bulk fermions in interaction with fermions on the branes. It is found that the dynamical fermion masses are generated at the natural (R.-S.) radius of the compactified extra space and may be made small compared with masses of the Kaluza-Klein modes which is of order of TeV.

hep-ph↗

arXiv1999

Structure of Chiral Phase Transitions at Finite Temperature in Abelian Gauge Theories

The mechanism of the chiral symmetry breaking is investigated in the strong-coupling Abelian gauge theories at finite temperature. The Schwinger-Dyson equation in Landau gauge is employed in the real time formalism and is solved numerically within the framework of the instantaneous exchange approximation including the effect of the hard thermal loop for the photon propagator. It is found that the chiral symmetry is broken below the critical temperature T for sufficiently large coupling. The chiral phase transition is found to be of the 2nd order and the phase diagram on the $T-α$ plane is obtained. It is investigated how the structure of the chiral phase transition is affected by the hard thermal loops in the photon propagator.

hep-ph↗

arXiv1998

Non-perturbative approach to the effective potential of the $λϕ^{4} theory at finite temperature

We construct a non-perturbative method to investigate the phase structure of the scalar theory at finite temperature. The derivative of the effective potential with respect to the mass square is expressed in terms of the full propagator. Under a certain approximation this expression reduces to the partial differential equation for the effective potential. We numerically solve the partial differential equation and obtain the effective potential non-perturbatively. It is found that the phase transition is of the second order. The critical exponents calculated in this method are consistent with the results obtained in Landau approximation.

hep-th↗