67 research outputs found
Magnetic catalysis and anisotropic confinement in QCD
The expressions for dynamical masses of quarks in the chiral limit in QCD in
a strong magnetic field are obtained. A low energy effective action for the
corresponding Nambu-Goldstone bosons is derived and the values of their decay
constants as well as the velocities are calculated. The existence of a
threshold value of the number of colors , dividing the theories with
essentially different dynamics, is established. For the number of colors , an anisotropic dynamics of confinement with the confinement
scale much less than and a rich spectrum of light glueballs is
realized. For of order or larger, a conventional confinement
dynamics takes place. It is found that the threshold value grows
rapidly with the magnetic field [ for ]. In contrast to QCD with a nonzero baryon density, there are no
principal obstacles for checking these results and predictions in lattice
computer simulations.Comment: 10 pages, 1 figure. REVTeX. Minor correction. To appear in Phys. Rev.
Constructing the fermion-boson vertex in QED3
We derive perturbative constraints on the transverse part of the
fermion-boson vertex in massive QED3 through its one loop evaluation in an
arbitrary covariant gauge. Written in a particular form, these constraints
naturally lead us to the first non-perturbative construction of the vertex,
which is in complete agreement with its one loop expansion in all momentum
regimes. Without affecting its one-loop perturbative properties, we also
construct an effective vertex in such a way that the unknown functions defining
it have no dependence on the angle between the incoming and outgoing fermion
momenta. Such a vertex should be useful for the numerical study of dynamical
chiral symmetry breaking, leading to more reliable results.Comment: 13 pages, 2 figure
Effect of Dynamical SU(2) Gluons to the Gap Equation of Nambu--Jona-Lasinio Model in Constant Background Magnetic Field
In order to estimate the effect of dynamical gluons to chiral condensate, the
gap equation of SU(2) gauged Nambu--Jona-Lasinio model, under a constant
background magnetic field, is investigated up to the two-loop order in 2+1 and
3+1 dimensions. We set up a general formulation allowing both cases of electric
as well as magnetic background field. We rely on the proper time method to
maintain gauge invariance. In 3+1 dimensions chiral symmetry breaking
(SB) is enhanced by gluons even in zero background magnetic field and
becomes much striking as the background field grows larger. In 2+1 dimensions
gluons also enhance SB but whose dependence on the background field is
not simple: dynamical mass is not a monotone function of background field for a
fixed four-fermi coupling.Comment: 20 pages, 5 figure
Dynamical Symmetry Breaking in Spaces with Constant Negative Curvature
By using the Nambu-Jona-Lasinio model, we study dynamical symmetry breaking
in spaces with constant negative curvature. We show that the physical reason
for zero value of critical coupling value in these spaces is
connected with the effective reduction of dimension of spacetime in the infrared region, which takes place for any dimension . Since
the Laplace-Beltrami operator has a gap in spaces with constant negative
curvature, such an effective reduction for scalar fields is absent and there
are not problems with radiative corrections due to scalar fields. Therefore,
dynamical symmetry breaking with the effective reduction of the dimension of
spacetime for fermions in the infrared region is consistent with the
Mermin-Wagner-Coleman theorem, which forbids spontaneous symmetry breaking in
(1 + 1)-dimensional spacetime.Comment: minor text changes, added new reference
Universality and the magnetic catalysis of chiral symmetry breaking
The hypothesis that the magnetic catalysis of chiral symmetry breaking is due
to interactions of massless fermions in their lowest Landau level is examined
in the context of chirally symmetric models with short ranged interactions. It
is argued that, when the magnetic field is sufficiently large, even an
infinitesimal attractive interaction in the appropriate channel will break
chiral symmetry.Comment: 24 pages, 6 figures, REVTeX. The final version with minor
corrections. To appear in Phys Rev D60 (1999
Faraday rotation in graphene
We study magneto--optical properties of monolayer graphene by means of
quantum field theory methods in the framework of the Dirac model. We reveal a
good agreement between the Dirac model and a recent experiment on giant Faraday
rotation in cyclotron resonance. We also predict other regimes when the effects
are well pronounced. The general dependence of the Faraday rotation and
absorption on various parameters of samples is revealed both for suspended and
epitaxial graphene.Comment: 10 pp; v2: typos corrected and references added, v3, v4: small
changes and more reference
On magnetic catalysis in even-flavor QED3
In this paper, we discuss the role of an external magnetic field on the
dynamically generated fermion mass in even-flavor QED in three space-time
dimensions. Based on some reasonable approximations, we present analytic
arguments on the fact that, for weak fields, the magnetically-induced mass
increases quadratically with increasing field, while at strong fields one
crosses over to a mass scaling logarithmically with the external field. We also
confirm this type of scaling behavior through quenched lattice calculations
using the non-compact version for the gauge field. Both the zero and finite
temperature cases are examined. A preliminary study of the fermion condensate
in the presence of magnetic flux tubes on the lattice is also included.Comment: 38 pages latex, 18 figures and a style file (axodraw) incorporated
(some clarifying remarks concerning the validity of the approximations made
and some references were added correcting an earlier version; no effect on
conclusions; version to appear in Phys. Rev. D.
QED in a Strong External Magnetic Field: Beyond the Constant Mass Approximation
We solve the Schwinger-Dyson equations for QED in 2+1 or 3+1 dimensions in
the presence of a strong homogeneous external magnetic field. The magnetic
field is assumed strong enough, so that the lowest Landau level approximation
holds, but the usual assumption of a momentum-independent self-energy is not
made. In 2+1 dimensions, the scaling with logarithm changes to a square root
dependence on the magnetic field, but the most spectacular result takes place
in 3+1 dimensions, where the constant mass approximation turns out to be
unreliable and the (momentum-dependent) dynamical mass is larger by several
orders of magnitude compared to what has been found till now using the constant
mass approximation.Comment: 21 pages, 8 figures, plain latex, references adde
Inverse magnetic catalysis in field theory and gauge-gravity duality
We investigate the surface of the chiral phase transition in the
three-dimensional parameter space of temperature, baryon chemical potential and
magnetic field in two different approaches, the field-theoretical
Nambu-Jona-Lasinio (NJL) model and the holographic Sakai-Sugimoto model. The
latter is a top-down approach to a gravity dual of QCD with an asymptotically
large number of colors and becomes, in a certain limit, dual to an NJL-like
model. Our main observation is that, at nonzero chemical potential, a magnetic
field can restore chiral symmetry, in apparent contrast to the phenomenon of
magnetic catalysis. This "inverse magnetic catalysis" occurs in the
Sakai-Sugimoto model and, for sufficiently large coupling, in the NJL model and
is related to the physics of the lowest Landau level. While in most parts our
discussion is a pedagogical review of previously published results, we include
new analytical results for the NJL approach and a thorough comparison of
inverse magnetic catalysis in the two approaches.Comment: 37 pages, 11 figures, to appear in Lect. Notes Phys. "Strongly
interacting matter in magnetic fields" (Springer), edited by D. Kharzeev, K.
Landsteiner, A. Schmitt, H.-U. Ye
Axial vector current in an electromagnetic field and low-energy neutrino-photon interactions
An expression for the axial vector current in a strong, slowly varying
electromagnetic field is obtained. We apply this expression to the construction
of the effective action for low-energy neutrino-photon interactions.Comment: 6 pages, references updated, final version to appear in Phys. Rev.
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