457 research outputs found
Gauge Coupling Instability and Dynamical Mass Generation in N=1 Supersymmetric QED(3)
Using superfield Dyson-Schwinger equations, we compute the infrared dynamics
of the semi-amputated full vertex, corresponding to the effective running gauge
coupling, in N-flavour {\mathcal N}=1 supersymmetric QED(3). It is shown that
the presence of a supersymmetry-preserving mass for the matter multiplet
stabilizes the infrared gauge coupling against oscillations present in the
massless case, and we therefore infer that the massive vacuum is thus selected
at the level of the (quantum) effective action. We further demonstrate that
such a mass can indeed be generated dynamically in a self-consistent way by
appealing to the superfield Dyson-Schwinger gap equation for the full matter
propagator.Comment: 14 pages ReVTeX; four axodraw figures incorporate
Degenerate Fermi gas perturbations at standard background cosmology
The hypothesis of a tiny fraction of the cosmic inventory evolving
cosmologically as a degenerate Fermi gas test fluid at some dominant
cosmological background is investigated. Our analytical results allow for
performing preliminary computations to the evolution of perturbations for
relativistic and non-relativistic test fluids. The density fluctuation,
, the fluid velocity divergence, , and an explicit expression
for the dynamics of the shear stress, , are obtained for a degenerate
Fermi gas in the background regime of radiation. Extensions to the dominance of
matter and to the CDM cosmological background are also investigated
and lessons concerning the formation of large structures of degenerate Fermi
gas are depicted.Comment: 20 pages, 4 figure
Reproducing neutrino effects on the matter power spectrum through a degenerate Fermi gas approach
Modifications on the predictions about the matter power spectrum based on the
hypothesis of a tiny contribution from a degenerate Fermi gas (DFG) test-fluid
to some dominant cosmological scenario are investigated. Reporting about the
systematic way of accounting for all the cosmological perturbations, through
the Boltzmann equation we obtain the analytical results for density
fluctuation, , and fluid velocity divergence, , of the DFG.
Small contributions to the matter power spectrum are analytically obtained for
the radiation-dominated background, through an ultra-relativistic
approximation, and for the matter-dominated and -dominated eras,
through a non-relativistic approximation. The results can be numerically
reproduced and compared with those of considering non-relativistic and
ultra-relativistic neutrinos into the computation of the matter power spectrum.
Lessons concerning the formation of large scale structures of a DFG are
depicted, and consequent deviations from standard CDM predictions for
the matter power spectrum (with and without neutrinos) are quantified.Comment: 28 pages, 06 figure
A note on dimer models and McKay quivers
We give one formulation of an algorithm of Hanany and Vegh which takes a
lattice polygon as an input and produces a set of isoradial dimer models. We
study the case of lattice triangles in detail and discuss the relation with
coamoebas following Feng, He, Kennaway and Vafa.Comment: 25 pages, 35 figures. v3:completely rewritte
Pattern densities in fluid dimer models
In this paper, we introduce a family of observables for the dimer model on a
bi-periodic bipartite planar graph, called pattern density fields. We study the
scaling limit of these objects for liquid and gaseous Gibbs measures of the
dimer model, and prove that they converge to a linear combination of a
derivative of the Gaussian massless free field and an independent white noise.Comment: 38 pages, 3 figure
Entropy of chains placed on the square lattice
We obtain the entropy of flexible linear chains composed of M monomers placed
on the square lattice using a transfer matrix approach. An excluded volume
interaction is included by considering the chains to be self-and mutually
avoiding, and a fraction rho of the sites are occupied by monomers. We solve
the problem exactly on stripes of increasing width m and then extrapolate our
results to the two-dimensional limit to infinity using finite-size scaling. The
extrapolated results for several finite values of M and in the polymer limit M
to infinity for the cases where all lattice sites are occupied (rho=1) and for
the partially filled case rho<1 are compared with earlier results. These
results are exact for dimers (M=2) and full occupation (\rho=1) and derived
from series expansions, mean-field like approximations, and transfer matrix
calculations for some other cases. For small values of M, as well as for the
polymer limit M to infinity, rather precise estimates of the entropy are
obtained.Comment: 6 pages, 7 figure
Non-linear Dynamics in QED_3 and Non-trivial Infrared Structure
In this work we consider a coupled system of Schwinger-Dyson equations for
self-energy and vertex functions in QED_3. Using the concept of a
semi-amputated vertex function, we manage to decouple the vertex equation and
transform it in the infrared into a non-linear differential equation of
Emden-Fowler type. Its solution suggests the following picture: in the absence
of infrared cut-offs there is only a trivial infrared fixed-point structure in
the theory. However, the presence of masses, for either fermions or photons,
changes the situation drastically, leading to a mass-dependent non-trivial
infrared fixed point. In this picture a dynamical mass for the fermions is
found to be generated consistently. The non-linearity of the equations gives
rise to highly non-trivial constraints among the mass and effective (`running')
gauge coupling, which impose lower and upper bounds on the latter for dynamical
mass generation to occur. Possible implications of this to the theory of
high-temperature superconductivity are briefly discussed.Comment: 29 pages LATEX, 7 eps figures incorporated, uses axodraw style.
Discussion on the massless case (section 2) modified; no effect on
conclusions, typos correcte
Pocket Monte Carlo algorithm for classical doped dimer models
We study the correlations of classical hardcore dimer models doped with
monomers by Monte Carlo simulation. We introduce an efficient cluster
algorithm, which is applicable in any dimension, for different lattices and
arbitrary doping. We use this algorithm for the dimer model on the square
lattice, where a finite density of monomers destroys the critical confinement
of the two-monomer problem. The monomers form a two-component plasma located in
its high-temperature phase, with the Coulomb interaction screened at finite
densities. On the triangular lattice, a single pair of monomers is not
confined. The monomer correlations are extremely short-ranged and hardly change
with doping.Comment: 6 pages, REVTeX
Quantum suppression of shot noise in field emitters
We have analyzed the shot noise of electron emission under strong applied
electric fields within the Landauer-Buttiker scheme. In contrast to the
previous studies of vacuum-tube emitters, we show that in new generation
electron emitters, scaled down to the nanometer dimensions, shot noise much
smaller than the Schottky noise is observable. Carbon nanotube field emitters
are among possible candidates to observe the effect of shot-noise suppression
caused by quantum partitioning.Comment: 5 pages, 1 fig, minor changes, published versio
Nonlinear Dynamical Stability of Newtonian Rotating White Dwarfs and Supermassive Stars
We prove general nonlinear stability and existence theorems for rotating star
solutions which are axi-symmetric steady-state solutions of the compressible
isentropic Euler-Poisson equations in 3 spatial dimensions. We apply our
results to rotating and non-rotating white dwarf, and rotating high density
supermassive (extreme relativistic) stars, stars which are in convective
equilibrium and have uniform chemical composition. This paper is a continuation
of our earlier work ([28])
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