227 research outputs found

### 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.Comment: 7pages, 3 figures, Talk given at the 2002 International Workshop on
"Strong Coupling Gauge Theories and Effective Field Theories" (SCGT 02),
Nagoya, Japan, 10-13 December 200

### Curvature Induced Phase Transition in a Four-Fermion Theory Using the Weak Curvature Expansion

Curvature induced phase transition is thoroughly investigated in a four-
fermion theory with $N$ components of fermions for arbitrary space-time
dimensions $(2 \leq D < 4)$. We adopt the $1/N$ expansion method and calculate
the effective potential for a composite operator $\bar{\psi}\psi$. The
resulting effective potential is expanded asymptotically in terms of the
space-time curvature $R$ by using the Riemann normal coordinate. We assume that
the space-time curves slowly and keep only terms independent of $R$ and terms
linear in $R$. Evaluating the effective potential it is found that the
first-order phase transition is caused and the broken chiral symmetry is
restored for a large positive curvature. In the space-time with a negative
curvature the chiral symmetry is broken down even if the coupling constant of
the four-fermion interaction is sufficiently small. We present the behavior of
the dynamically generated fermion mass. The critical curvature, $R_{cr}$, which
divides the symmetric and asymmetric phases is obtained analytically as a
function of the space-time dimension $D$. At the four-dimensional limit our
result $R_{cr}$ agrees with the exact results known in de Sitter space and
Einstein universe.Comment: 19 pages, uses LaTeX, eepic.st

### 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, $2\leq D<4$.Comment: 7 pages, 6 figures, Contribution to the proceedings of 2009 Nagoya
Global COE Workshop "Strong Coupling Gauge Theories in LHC Era (SCGT09)

### Boltzmann Equation for Relativistic Neutral Scalar Field in Non-equilibrium Thermo Field Dynamics

A relativistic neutral scalar field is investigated on the basis of the
Schwinger-Dyson equation in the non-equilibrium thermo field dynamics. A time
evolution equation for a distribution function is obtained from a
diagonalization condition for the Schwinger-Dyson equation. An explicit
expression of the time evolution equation is calculated in the $\lambda\phi^4$
interaction model at the 2-loop level. The Boltzmann equation is derived for
the relativistic scalar field. We set a simple initial condition and
numerically solve the Boltzmann equation and show the time evolution of the
distribution function and the relaxation time.Comment: 23 pages, 9 figure

### Parameter fitting in three-flavor Nambu--Jona-Lasinio model with various regularizations

We study the three-flavor Nambu--Jona-Lasinio model with various
regularization procedures. We perform parameter fitting in each regularization
and apply the obtained parameter sets to evaluate various physical quantities,
several light meson masses, decay constant and the topological susceptibility.
The model parameters are adopted even at very high cutoff scale compare to the
hadronic scale to study the asymptotic behavior of the model. It is found that
all the regularization methods except for the dimensional one actually lead
reliable physical predictions for the kaon decay constant, sigma meson mass and
topological susceptibility without restricting the ultra-violet cutoff below
the hadronic scale.Comment: 22 pages, 10 figure

### 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 $T$-$\mu$, $H$-$T$ and $\mu$-$H$ planes. The external magnetic field
modifies the phase structure. It is found that a new phase appears for a large
chemical potential.Comment: 16 pages, 10 figure

### 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.Comment: 7 pages, 8 figures, To appear in the proceedings of the Workshop on
Origin of Mass and Strong Coupling Gauge Theories, Nagoya, Japan, 21-24
November 200

### 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.Comment: 6 pages, 2 figures, Poster talk presented at the Workshop on Finite
Density QCD at Nara, Japan, 10-12 July 2003; replaced two reference

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