Deconstructing the vertex Ansatz in three dimensional quantum electrodynamics

We consider the problem of designing an Ansatz for the fermion-photon vertex function, using three-dimensional quantum electrodynamics as a test case. In many existing studies, restrictions have been placed on the form of the vertex Ansatz by making the unsubstantiated assumption that in the quenched, massless limit the Landau gauge Dyson-Schwinger equations admit a trivial solution. We demonstrate, without recourse to this assumption, the existence of a non-local gauge in which the fermion propagator is the bare propagator. This result is used to provide a viable Ansatz for part of the vertex function.Comment: 14 pages, 2 postscript figures, uses epsfig.st

The analytic structure of heavy quark propagators

The renormalised quark Dyson-Schwinger equation is studied in the limit of the renormalised current heavy quark mass m_R --> infinity. We are particularly interested in the analytic pole structure of the heavy quark propagator in the complex momentum plane. Approximations in which the quark-gluon vertex is modelled by either the bare vertex or the Ball-Chiu Ansatz, and the Landau gauge gluon propagator takes either a gaussian form or a gaussian form with an ultraviolet asymptotic tail are used.Comment: 21 pages Latex and 5 postscript figures. The original version of this paper has been considerably extended to include a formalism dealing with the renormalised heavy quark Dyson-Schwinger equation and uses a more realistic Ansatz for the gluon propagator

Vector Positronium States in QED3

The homogeneous Bethe-Salpeter equation is solved in the quenched ladder approximation for the vector positronium states of 4-component quantum electrodynamics in 2 space and 1 time dimensions. Fermion propagator input is from a Rainbow approximation Dyson-Schwinger solution, with a broad range of fermion masses considered. This work is an extension of earlier work on the scalar spectrum of the same model. The non-relativistic limit is also considered via the large fermion mass limit. Classification of states via their transformation properties under discrete parity transformations allows analogies to be drawn with the meson spectrum of QCD.Comment: 24 pages, 2 encapsulated postscript figure

Exactly solvable strings in Minkowski spacetime

We study the integrability of the equations of motion for the Nambu-Goto strings with a cohomogeneity-one symmetry in Minkowski spacetime. A cohomogeneity-one string has a world surface which is tangent to a Killing vector field. By virtue of the Killing vector, the equations of motion can be reduced to the geodesic equation in the orbit space. Cohomogeneity-one strings are classified into seven classes (Types I to VII). We investigate the integrability of the geodesic equations for all the classes and find that the geodesic equations are integrable. For Types I to VI, the integrability comes from the existence of Killing vectors on the orbit space which are the projections of Killing vectors on Minkowski spacetime. For Type VII, the integrability is related to a projected Killing vector and a nontrivial Killing tensor on the orbit space. We also find that the geodesic equations of all types are exactly solvable, and show the solutions.Comment: 11 pages, a reference added, some points clarifie

QED in external fields, a functional point of view

A functional partial differential equation is set for the proper graphs generating functional of QED in external electromagnetic fields. This equation leads to the evolution of the proper graphs with the external field amplitude and the external field gauge dependence of the complete fermion propagator and vertex is derived non-perturbativally.Comment: 8 pages, published versio

Adsorption models of hybridization and post-hybridisation behaviour on oligonucleotide microarrays

Analysis of data from an Affymetrix Latin Square spike-in experiment indicates that measured fluorescence intensities of features on an oligonucleotide microarray are related to spike-in RNA target concentrations via a hyperbolic response function, generally identified as a Langmuir adsorption isotherm. Furthermore the asymptotic signal at high spike-in concentrations is almost invariably lower for a mismatch feature than for its partner perfect match feature. We survey a number of theoretical adsorption models of hybridization at the microarray surface and find that in general they are unable to explain the differing saturation responses of perfect and mismatch features. On the other hand, we find that a simple and consistent explanation can be found in a model in which equilibrium hybridization followed by partial dissociation of duplexes during the post-hybridization washing phase.Comment: 26 pages, 6 figures, some rearrangement of sections and some additions. To appear in J.Phys.(condensed matter

Prosthesis use is associated with reduced physical self-disgust in limb amputees

Self-disgust is an emotion schema negatively affecting people’s body image and is triggered by bodily imperfections and deviations from the “normal” body envelope. In this study, we explore the idea that “normalising” the body in those with limb amputations via the prosthesis would be linked to reduced self-directed disgust. An international clinical community sample (N = 83) with mostly lower limb amputations completed measures about their demographics, prosthesis, adjustment, body image disturbance, psychological distress, and self-directed disgust in a survey design. Consistent with the “normalising” hypothesis, correlation and bootstrapped regression models revealed, first, that frequency of prosthesis use was significantly and negatively associated with physical self-disgust. Second, prosthesis use significantly mediated the exogenous effect of time since amputation on physical self-disgust. These results emphasise the psychological value of the prosthesis beyond its functional use, and stress its importance in normalising the body envelope in those with limb amputations, which may in turn promote psychological well-being

Conservation-laws-preserving algorithms for spin dynamics simulations

We propose new algorithms for numerical integration of the equations of motion for classical spin systems with fixed spatial site positions. The algorithms are derived on the basis of a mid-point scheme in conjunction with the multiple time staging propagation. Contrary to existing predictor-corrector and decomposition approaches, the algorithms introduced preserve all the integrals of motion inherent in the basic equations. As is demonstrated for a lattice ferromagnet model, the present approach appears to be more efficient even over the recently developed decomposition method.Comment: 13 pages, 2 figure

Survey of J=0,1 mesons in a Bethe-Salpeter approach

The Bethe-Salpeter equation is used to comprehensively study mesons with J=0,1 and equal-mass constituents for quark masses from the chiral limit to the b-quark mass. The survey contains masses of the ground states in all corresponding J^{PC} channels including those with "exotic" quantum numbers. The emphasis is put on each particular state's sensitivity to the low- and intermediate-momentum, i.e., long-range part of the strong interaction.Comment: 8 pages, 4 figure

Series Expansions for three-dimensional QED

Strong-coupling series expansions are calculated for the Hamiltonian version of compact lattice electrodynamics in (2+1) dimensions, with 4-component fermions. Series are calculated for the ground-state energy per site, the chiral condensate, and the masses of `glueball' and positronium states. Comparisons are made with results obtained by other techniques.Comment: 13 figure