68,729 research outputs found
Microscopic spectral density in random matrix models for chiral and diquark condensation
We examine random matrix models of QCD which are capable of supporting both
chiral and diquark condensation. A numerical study of the spectral densities
near zero virtuality shows that the introduction of color in the interactions
does not alter the one-body results imposed by chiral symmetry. A model with
three colors has the spectral density predicted for the chiral ensemble with a
Dyson index beta = 2; a pseudoreal model with two colors exhibits the spectral
density of the chiral ensemble with beta = 1.Comment: 6 pages, 3 eps figures, uses revtex4 and graphicx. v2 : minor
editions, Fig. 3 shows relative deviations rather than absolute. Version to
appear in PR
Random matrix model for antiferromagnetism and superconductivity on a two-dimensional lattice
We suggest a new mean field method for studying the thermodynamic competition
between magnetic and superconducting phases in a two-dimensional square
lattice. A partition function is constructed by writing microscopic
interactions that describe the exchange of density and spin-fluctuations. A
block structure dictated by spin, time-reversal, and bipartite symmetries is
imposed on the single-particle Hamiltonian. The detailed dynamics of the
interactions are neglected and replaced by a normal distribution of random
matrix elements. The resulting partition function can be calculated exactly.
The thermodynamic potential has a structure which depends only on the spectrum
of quasiparticles propagating in fixed condensation fields, with coupling
constants that can be related directly to the variances of the microscopic
processes. The resulting phase diagram reveals a fixed number of phase
topologies whose realizations depend on a single coupling-parameter ratio,
alpha. Most phase topologies are realized for a broad range of values of alpha
and can thus be considered robust with respect to moderate variations in the
detailed description of the underlying interactions.Comment: 21 pages, 8 figures, RevTex 4. Minor grammatical errors corrected in
the last versio
Random matrix models for chiral and diquark condensation
We consider random matrix models for the thermodynamic competition between
chiral symmetry breaking and diquark condensation in QCD at finite temperature
and finite baryon density. The models produce mean field phase diagrams whose
topology depends solely on the global symmetries of the theory. We discuss the
block structure of the interactions that is imposed by chiral, spin, and color
degrees of freedom and comment on the treatment of density and temperature
effects. Extension of the coupling parameters to a larger class of theories
allows us to investigate the robustness of the phase topology with respect to
variations in the dynamics of the interactions. We briefly study the phase
structure as a function of coupling parameters and the number of colors.Comment: 6 pages, 2 figures, proceedings of the workshop "Three Days of
Hadronic Physics", Joint Meeting Heidelberg-Liege-Paris-Rostock,
16/12/2004-18/12/2004, Sol Cress, Spa, Belgium. v2: typographical errors
corrected in reference
Electric-Magnetic Duality and Topological Insulators
We work out the action of the SL(2,Z) electric-magnetic duality group for an
insulator with a non-trivial permittivity, permeability and theta-angle. This
theory has recently been proposed to be the correct low-energy effective action
for topological insulators. As applications, we give manifestly SL(2,Z)
covariant expressions for the Faraday rotation at orthogonal incidence at the
interface of two such materials, as well as for the induced magnetic and
electric charges, slightly clarifying the meaning of expressions previously
derived in the literature. We also use electric-magnetic duality to find a
gravitational dual for a strongly coupled version of this theory using the
AdS/CFT correspondence.Comment: 4 pages; version accepted by PR
Finding the Pion in the Chiral Random Matrix Vacuum
The existence of a Goldstone boson is demonstrated in chiral random matrix
theory. After determining the effective coupling and calculating the scalar and
pseudoscalar propagators, a random phase approximation summation reveals the
massless pion and massive sigma modes expected whenever chiral symmetry is
spontaneously broken.Comment: 3 pages, 1 figure, revte
Propagation of exciton pulses in semiconductors
Using a toy model, we examine the propagation of excitons in CuO, which
form localized pulses under certain experimental conditions. The formation of
these waves is attributed to the effect of dispersion, non-linearity and the
coupling of the excitons to phonons, which acts as a dissipative mechanism.Comment: 5 pages, 4 ps figures, RevTe
Vortices in Bose-Einstein condensates with anharmonic confinement
We examine an effectively repulsive Bose-Einstein condensate of atoms, that
rotates in a quadratic-plus-quartic trapping potential. We investigate the
phase diagram of the system as a function of the angular frequency of rotation
and of the coupling constant, demonstrating that there are phase transitions
between multiply- and singly-quantized vortex states. The derived phase diagram
is shown to be universal and exact in the limits of small anharmonicity and
weak coupling constant.Comment: 4 pages, 2 ps figures, RevTe
A simple variational principle for classical spinning particle with anomalous magnetic momentum
We obtain Bargmann-Michel-Telegdi equations of motion of classical spinning
particle using Lagrangian variational principle with Grassmann variables.Comment: 3 pages, late
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