9 research outputs found
Schwinger-Dyson Equations in 2D Induced Gravity in Covariant Gauges
We formulate the Schwinger-Dyson equations in the ladder approximation for 2D
induced quantum gravity with fermions using covariant gauges of harmonic type.
It is shown that these equations can be formulated consistently in a gauge of
Landau type (for negative cosmological constant). A numerical analysis of the
equations hints towards the possibility of chiral symmetry breaking, depending
on the value of the coupling constant.Comment: 11 pages, LaTeX file, 2 figures (available upon request), 94/7/2
Chiral Symmetry Breaking in the Nambu-Jona-Lasinio Model in Curved Spacetime
The phase structure of the Nambu-Jona-Lasinio model in curved spacetime
is considered to leading order in the --expansion and in the linear
curvature approximation. The possibility of a curvature-induced first-order
phase transition is investigated numerically. The dynamically generated
fermionic mass is calculated for some values of the curvature.Comment: 7 pages, LaTeX file, 4 figures (appended as compressed postscript
file), Jan. 199
Dynamical symmetry restoration for a higher-derivative four-fermion model in an external electromagnetic field
A four-fermion model with additional higher-derivative terms is investigated
in an external electromagnetic field. The effective potential in the leading
order of large-N expansion is calculated in external constant magnetic and
electric fields.
It is shown that, in contrast to the former results concerning the universal
character of "magnetic catalysis" in dynamical symmetry breaking, in the
present higher-derivative model the magnetic field restores chiral symmetry
broken initially on the tree level. Numerical results describing a second-order
phase transition that accompanies the symmetry restoration at the quantum level
are presented.Comment: LaTeX, 14 pages, 4 ps-figure
Dynamical symmetry breaking in the external gravitational and constant magnetic fields
We investigate the effects of the external gravitational and constant
magnetic fields to the dynamical symmetrybreaking. As simple models of the
dynamical symmetry breaking we consider the Nambu-Jona-Lasinio (NJL) model and
the supersymmetric Nambu-Jona-Lasinio (SUSY NJL) model non-minimally
interacting with the external gravitational field and minimally interacting
with constant magnetic field. The explicit expressions for the scalar and
spinor Green functions are found up to the linear terms on the spacetime
curvature and exactly for a constant magnetic field. We obtain the effective
potential of the above models from the Green functions in the magnetic field in
curved spacetime. Calculating the effective potential numerically with the
varying curvature and/or magnetic fields we show the effects of the external
gravitational and magnetic fields to the phase structure of the theories. In
particular, increase of the curvature in the spontaneously broken chiral
symmetry phase due to the fixed magnetic field makes this phase to be less
broken. On the same time strong magnetic field quickly induces chiral symmetry
breaking even at the presence of fixed gravitational field within nonbroken
phase.Comment: 23 pages, Latex, epic.sty and eepic.sty are use
Chiral symmetry breaking in d=3 NJL model in external gravitational and magnetic fields
The phase structure of Nambu-Jona-Lasinio model in curved spacetime
with magnetic field is investigated in the leading order of the -expansion
and in linear curvature approximation (an external magnetic field is treated
exactly). The possibility of the chiral symmetry breaking under the combined
action of the external gravitational and magnetic fields is shown explicitly.
At some circumstances the chiral symmetry may be restored due to the
compensation of the magnetic field by the gravitational field.Comment: 7 pages, LaTe
Dynamical symmetry breaking in the Nambu-Jona-Lasino model with external gravitational and constant electric fields
An investigation of the Nambu-Jona-Lasino model with external constant
electric and weak gravitational fields is carried out in three- and four-
dimensional spacetimes. The effective potential of the composite bifermionic
fields is calculated keeping terms linear in the curvature, while the electric
field effect is treated exactly by means of the proper- time formalism.
A rich dynamical symmetry breaking pattern, accompanied by phase transitions
which are ruled, independently, by both the curvature and the electric field
strength is found. Numerical simulations of the transitions are presented.Comment: 20 pages, LaTeX, 6 .ps-figures, Final version published in "Classical
and Quantum Gravity