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L. C. R. Wijewardhana

Publications and source records attributed to L. C. R. Wijewardhana.

71 records · Page 4Linked to original sources
arXiv1999

Schwinger-Dyson Approach to Color Superconductivity in Dense QCD

The problem of color superconductivity in dense QCD is reconsidered in the improved rainbow approximation to the Schwinger-Dyson equation. The effect of the unscreened magnetic modes of gluons on the value of the color condensate is studied. In particular, it is shown that, at sufficiently large values of the chemical potential, these modes lead to the enhancement of the superconducting order parameter. The interplay between the instanton induced interaction and the one-gluon induced one in color superconductivity is discussed.

hep-ph↗
arXiv1999

On gap equations and color-flavor locking in cold dense QCD with three massless flavors

The superconductivity in cold dense QCD with three massless flavors is analyzed in the framework of the Schwinger-Dyson equation. The set of two coupled gap equations for the color antitriplet, flavor antitriplet (bar{3},bar{3}) and the color sextet, flavor sextet (6,6) order parameters is derived. It is shown that the antitriplet-antitriplet gives the dominant contribution to the color-flavor locked order parameter, while the sextet-sextet is small but nonzero.

hep-ph↗
arXiv1999

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.

hep-th↗
arXiv1998

The Phase Structure of an SU(N) Gauge Theory with N_f Flavors

We investigate the chiral phase transition in SU(N) gauge theories as the number of quark flavors, $N_f$, is varied. We argue that the transition takes place at a large enough value of $N_f$ so that it is governed by the infrared fixed point of the $β$ function. We study the nature of the phase transition analytically and numerically, and discuss the spectrum of the theory as the critical value of $N_f$ is approached in both the symmetric and broken phases. Since the transition is governed by a conformal fixed point, there are no light excitations on the symmetric side. We extend previous work to include higher order effects by developing a renormalization group estimate of the critical coupling.

hep-ph↗
arXiv1998

Detecting Event Horizons and Stationary Surfaces

We have investigated the behavior of three curvature invariants for Schwarzschild, Reissner-Nordstrøm, Kerr, and Kerr-Newman black holes. We have also studied these invariants for a Schwarzschild-de Sitter space-time, the $γ$ metric, and for a 2+1 charged dimensional black hole. The invariants are $I_{1}=R_{αβμν;λ}R^{αβμν;λ}$, $I_{2}=R_{μν;λ} R^{μν;λ}$, and $I_{3}=C_{αβμν;λ}C^{αβμν;λ}$. For all but the Kerr-Newman case these invariants serve as either horizon or stationary surface detectors. The Kerr-Newman case is more complicated. We show that $I_{1}$ vanishs on the horizon in any space-time with a Schwarzschild like metric.

gr-qc↗
arXiv1998

Chiral Symmetry Breaking in 2+1 dimensions due to Sphalerons

In 2+1 dimensional gauge thories with $SU(N_c)$ color and $2N_f$ flavors of quarks in the fundamental representation, sphalerons, if present may lead to quark condensation and chiral symmetry breaking. The effect is similar to instanton induced chiral symmetry breaking in 3+1 dimensions and is due to the interaction of quark propagators with sphalerons. The existence of sphalerons requires that color symmetries be broken by a Higgs in the fundamental representation. We show that the sphaleron effect may persist for arbitrarily large $N_f$ but vanishes along with the mass of the gauge fields corresponding to broken generators of $SU(N_c)$. The effect is inherently non-Abelian and absent for QED.

hep-ph↗
arXiv1998

Phase transition induced by a magnetic field

The magnetic catalysis of discrete chiral symmetry breaking in the 2+1 dimensional Nambu-Jona-Lasinio model is analyzed. A particular attention is paid to a possible application of the effect in solid state physics. The fermion contribution to the thermal conductivity as a function of the dynamical mass (energy gap in the spectrum) is estimated and is shown to be suppressed when a non-zero order parameter develops.

hep-ph↗
arXiv1998

The next to leading order effective potential in the 2+1 dimensional Nambu-Jona-Lasinio model at finite temperature

The finite temperature effective potential in the 2+1 dimensional Nambu-Jona-Lasinio model is constructed up to the next to leading order in the large $N$ expansion, where $N$ is the number of flavors in the model. The distinctive feature of the analysis is an inclusion of an additional scalar field, which allows us to circumvent the well known, and otherwise unavoidable problem with the imaginary contribution to the effective potential. In accordance with the Mermin-Wagner-Coleman theorem, applied to the dimensionally reduced subsystem of the zero Matsubara modes of the composite boson fields, the finite temperature effective potential reveals a global minimum at the zero of the composite order parameter. This allows us to conclude that the continuous global symmetry of the NJL model is not broken for any arbitrarily small, finite temperature.

hep-ph↗
arXiv1997

Postmodern Technicolor

Using new insights into strongly coupled gauge theories arising from analytic calculations and lattice simulations, we explore a framework for technicolor model building that relies on a non-trivial infrared fixed point, and an essential role for QCD. Interestingly, the models lead to a simple relation between the electroweak scale and the QCD confinement scale, and to the possible existence of exotic leptoquarks with masses of several hundred GeV.

hep-ph↗
arXiv1997

The Zero Temperature Chiral Phase Transition in SU(N) Gauge Theories

We investigate the zero temperature chiral phase transition in an SU(N) gauge theory as the number of fermions $N_f$ is varied. We argue that there exists a critical number of fermions $N_f^c$, above which there is no chiral symmetry breaking or confinement, and below which both chiral symmetry breaking and confinement set in. We estimate $N_f^c$ and discuss the nature of the phase transition.

hep-ph↗
arXiv1997

An evaluation of the analytic continuation by duality technique

In Nucl. Phys. B391 (1993) 127, the value of the oblique correction parameter S for walking technicolor theories was estimated using a technique called Analytic Continuation by Duality (ACD). We apply the ACD technique to the perturbative vacuum polarization function and find that it fails to reproduce the well known result S=1/6π. This brings into question the reliability of the ACD technique and the ACD estimate of S.

hep-ph↗
arXiv1997

ACD estimation of the S parameter revisited

The analytic continuation by duality (ACD) technique has been used to estimate the electroweak S parameter in technicolor models. In this letter, we investigate the reliability of this method by applying it to some toy models with known spectra. We find that in most instances the technique cannot be trusted to give a reliable result.

hep-ph↗
arXiv1995

Gauged Yukawa Matrix Models and 2-Dimensional Lattice Theories

We argue that chiral symmetry breaking in three dimensional QCD can be identified with Néel order in 2-dimensional quantum antiferromagnets. When operators which drive the chiral transition are added to these theories, we postulate that the resulting quantum critical behavior is in the universality class of gauged Yukawa matrix models. As a consequence, the chiral transition is typically of first order, although for a limited class of parameters it can be second order with computable critical exponents.

hep-ph↗
arXiv1995

New Universality Classes for Quantum Critical Behavior

We use the epsilon expansion to explore a new universality class of second order quantum phase transitions associated with a four-dimensional Yukawa field theory coupled to a traceless Hermitean matrix scalar field. We argue that this class includes four-fermi models in $2<D<4$ dimensions with $SU(N_F)\times U(N)$ symmetry and a U(N) scalar, $SU(N_F)$ iso-vector 4-fermi coupling. The epsilon expansion indicates that there is a second order phase transition for $N\geq N^*(N_F)$, where $N^*(N_F)\simeq.27N_F$ if $N_F\to\infty$.

hep-ph↗
arXiv1995

Phase Transitions and Mass Generation in 2+1 Dimensions

The possibility that the epsilon expansion can predict the order of phase transitions in three dimensional field theories is examined. For a Hermitean matrix-valued order parameter, the epsilon expansion predicts fluctuation induced first order phase transitions. We analyze two 2+1-dimensional quantum field theories which exhibit spontaneous symmetry breaking and have martix order parameters. Using the large $N$ expansion, we show that these models exhibit second order transitions and discuss the implications for the chiral symmetry breaking transition in 2+1-dimensional QCD for a critical number of quark flavors.

hep-ph↗
arXiv1994

2+1 Dimensional QED and a Novel Phase Transition

We investigate the chiral phase transition in 2+1 dimensional QED. Previous gap equation and lattice Monte-Carlo studies of symmetry breaking have found that symmetry breaking ceases to occur when the number of fermion flavors exceeds a critical value. Here we focus on the order of the transition. We find that there are no light scalar degrees of freedom present as the critical number of flavors is approached from above (in the symmetric phase). Thus the phase transition is not second order, rendering irrelevant the renormalization group arguments for a fluctuation induced transition. However, the order parameter vanishes continuously in the broken phase, so this transition is also unlike a conventional first order phase transition.

hep-ph↗