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

Electromagnetic Form Factors of Charged and Neutral Kaons

The charged and neutral kaon form factors are calculated as a phenomenological application of the QCD Dyson-Schwinger equations. The results are compared with the pion form factor calculated in the same framework and yield \mbox{$F_{K^\pm}(Q^2) > F_{\pi^\pm}(Q^2)$} on \mbox{$Q^2\in[0,3]$~GeV$^2$}; and a neutral kaon form factor that is similar in form and magnitude to the neutron charge form factor. These results are sensitive to the difference between the kaon and pion Bethe-Salpeter amplitude and the $u$- and $s$-quark propagation characteristics.Comment: 11 Pages, 2 figures, REVTEX, uses epsfig. No chang

Nucleon form factors and a nonpointlike diquark

Nucleon form factors are calculated on q^2 in [0,3] GeV^2 using an Ansatz for the nucleon's Fadde'ev amplitude motivated by quark-diquark solutions of the relativistic Fadde'ev equation. Only the scalar diquark is retained, and it and the quark are confined. A good description of the data requires a nonpointlike diquark correlation with an electromagnetic radius of 0.8 r_pi. The composite, nonpointlike nature of the diquark is crucial. It provides for diquark-breakup terms that are of greater importance than the diquark photon absorption contribution.Comment: 5 pages, REVTEX, epsfig, 3 figure

Mass singularity and confining property in QED3QED_3

We discuss the properties of the position space fermion propagator in three dimensional QED which has been found previouly based on Ward-Takahashi-identity for soft-photon emission vertex and spectral representation.There is a new type of mass singularity which governs the long distance behaviour.It leads the propagator vanish at large distance.This term corresponds to dynamical mass in position space.Our model shows confining property and dynamical mass generation for arbitrary coupling constant.Since we used dispersion retation in deriving spectral function there is a physical mass which sets a mass scale.For finite cut off we obtain the full propagator in the dispersion integral as a superposition of different massses.Low energy behaviour of the proagator is modified to decrease by position dependent mass.In the limit of zero infrared cut-off the propagator vanishes with a new kind of infrared behaviour.Comment: 22pages,4figures,revtex4,Notational sloppiness are crrected.Submitted to JHE

Diquarks: condensation without bound states

We employ a bispinor gap equation to study superfluidity at nonzero chemical potential: mu .neq. 0, in two- and three-colour QCD. The two-colour theory, QC2D, is an excellent exemplar: the order of truncation of the quark-quark scattering kernel: K, has no qualitative impact, which allows a straightforward elucidation of the effects of mu when the coupling is strong. In rainbow-ladder truncation, diquark bound states appear in the spectrum of the three-colour theory, a defect that is eliminated by an improvement of K. The corrected gap equation describes a superfluid phase that is semi-quantitatively similar to that obtained using the rainbow truncation. A model study suggests that the width of the superfluid gap and the transition point in QC2D provide reliable quantitative estimates of those quantities in QCD.Comment: 7 pages, 3 figures, REVTEX, epsfi

Strong Decays of Light Vector Mesons

The vector meson strong decays rho-->pi pi, phi-->KK, and K^star-->pi K are studied within a covariant approach based on the ladder-rainbow truncation of the QCD Dyson--Schwinger equation for the quark propagator and the Bethe--Salpeter equation for the mesons. The model preserves the one-loop behavior of QCD in the ultraviolet, has two infrared parameters, and implements quark confinement and dynamical chiral symmetry breaking. The 3-point decay amplitudes are described in impulse approximation. The Bethe--Salpeter study motivates a method for estimating the masses for heavier mesons within this model without continuing the propagators into the complex plane. We test the accuracy via the rho, phi and K^{star} masses and then produce estimates of the model results for the a_1 and b_1 masses as well as the mass of the proposed exotic vector pi_1(1400).Comment: Submitted for publication; 10x2-column pages, REVTEX 4, 3 .eps files making 3fig

Selected nucleon form factors and a composite scalar diquark

A covariant, composite scalar diquark, Fadde'ev amplitude model for the nucleon is used to calculate pseudoscalar, isoscalar- and isovector-vector, axial-vector and scalar nucleon form factors. The last yields the nucleon sigma-term and on-shell sigma-nucleon coupling. The calculated form factors are soft, and the couplings are generally in good agreement with experiment and other determinations. Elements in the dressed-quark-axial-vector vertex that are not constrained by the Ward-Takahashi identity contribute ~20% to the magnitude of g_A. The calculation of the nucleon sigma-term elucidates the only unambiguous means of extrapolating meson-nucleon couplings off the meson mass-shell.Comment: 12 pages, REVTEX, 5 figures, epsfi

Three point SUSY Ward identities without Ghosts

We utilise a non-local gauge transform which renders the entire action of SUSY QED invariant and respects the SUSY algebra modulo the gauge-fixing condition, to derive two- and three-point ghost-free SUSY Ward identities in SUSY QED. We use the cluster decomposition principle to find the Green's function Ward identities and then takes linear combinations of the latter to derive identities for the proper functions.Comment: 20 pages, no figures, typos correcte

Singular Liouville fields and spiky strings in \rr^{1,2} and SL(2,\rr)

The closed string dynamics in \rr^{1,2} and SL(2,\rr) is studied within the scheme of Pohlmeyer reduction. In both spaces two different classes of string surfaces are specified by the structure of the fundamental quadratic forms. The first class in \rr^{1,2} is associated with the standard lightcone gauge strings and the second class describes spiky strings and their conformal deformations on the Virasoro coadjoint orbits. These orbits correspond to singular Liouville fields with the monodromy matrixes $\pm I$. The first class in SL(2,\rr) is parameterized by the Liouville fields with vanishing chiral energy functional. Similarly to \rr^{1,2}, the second class in SL(2,\rr) describes spiky strings, related to the vacuum configurations of the SL(2,\rr)/U(1) coset model.Comment: 37 p. 6 fi

Gravitational radiation from monopoles connected by strings

Monopole-antimonopole pairs connected by strings can be formed as topological defects in a sequence of cosmological phase transitions. Such hybrid defects typically decay early in the history of the universe but can still generate an observable background of gravitational waves. We study the spectrum of gravitational radiation from these objects both analytically and numerically, concentrating on the simplest case of an oscillating pair connected by a straight string.Comment: 18 pages, RevTex and 2 postscript figures. Submitted to Phys. Rev.