Showing papers on "Vertex function published in 1988"

Ultraviolet-improved gauge technique and the effective quark propagator in QCD.

Abstract: The gauge technique linearizes the Schwinger-Dyson equation by replacing the full vertex with a longitudinal vertex, satisfying the Ward identity. We show how to improve the standard gauge-technique treatment which is nonrenormalizable, by adding a conserved transverse vertex to the longitudinal vertex thereby removing all overlapping divergences from the Schwinger-Dyson equation in QCD. The improved gauge technique preserves multiplicative renormalizability and gauge covariance. Such a modified version of the gauge technique is used to solve the Schwinger-Dyson equation for the effective quark propagator of QCD, S(p), in the ultraviolet regime. For nonzero current-quark mass m, a solution is found that agrees with renormalization-group analysis, while a similar solution appears for the m = 0 case corresponding to dynamical chiral-symmetry breaking (i.e., a nonzero dynamical quark mass M(p)).

Still more corrections to the topological mass.

Abstract: In an attempt to demonstrate that any parity-nonconserving term can be expected to contribute to the axial-vector part of the current-correlation function, the coupling of charged vector mesons is considered. It is confirmed that parity nonconservation does in fact affect the relevant form factor at zero momentum transfer. Although the result is generally divergent, a finite correction is obtained when a certain sum rule on inverse masses is satisfied. In that limit a single expression is seen to unify the spin-0, spin-\textonehalf{}, and spin-1 contributions to the so-called topological mass.

Vertex functions in the path integral formalism of open string theories

Abstract: We study a systematic method to obtain the general vertex functions (of Neveu-Schwarz sector), which are used in the covariant path integral approach to the open bosonic and superstring theories. For the superstring the superspace formulation in the Wess-Zumino gauge is used to construct the vertices at the boundaries of world sheets. For both theories the vertex functions are explicitly obtained for the first four mass levels and coincide with those in the operator formalism.

Description of the three-nucleon system in the quark compound bag method and the vertex function for the decay 3He to pd

Abstract: The NN potentials derived within quark compound bag (QCB) method are used to calculate the vertex function G(p2) for the virtual decay 3He to pd. It is shown that even in its simplest version the QCB method provides a realistic description of G(p2) which agrees with the latest experimental data. The effects of the six quark bag corrections to G(p2) at p

Anomalies of the products of vertex functions in the superstring theories

Abstract: We obtain the two-dimensional anomalous transforms of the products of several vertex functions (of Neveu-Schwarz sector) in the path integral formulation of closed superstrings: type II super and heterotic strings. The products of vertex functions are free from local anomalies except for Weyl anomalies. In the presence of background fields this kind of Weyl anomalies leads to interaction terms in the background field equations of motion, which are derived by the requirement of the cancellation of Weyl anomalies.

Instabilities of the chiral-symmetry-breaking ground state in a truncation-free expansion.

Abstract: We use the composite-field effective-action method to examine the stability of the chiral-symmetry-breaking vacua in a QED-like model of interacting fermion fields. Unlike most of the existing approaches, ours does not rely on the truncated Baker-Johnson-Willey expansion. Instead, we break the hierarchy of the Dyson-Schwinger equations by the requirement that the vertex function is dominated by the contributions from the vicinity of the mass shell of the exchanged gluon and that it explicitly satisfies the Ward identity. The composite-field effective potential is then expanded in terms of the eigenfunctions of the Bethe-Salpeter equation. The signature of the second derivatives of the effective potential shows that the broken-symmetry vacua are unstable.

Imaginary parts of coupled electron and phonon propagators.

Abstract: Quasiparticle and phonon damping rates due to the electron-phonon and Coulomb interactions are obtained directly from the self-energy formalism of strong-coupling theory. This accounts for all processes involving phonon or quasiparticle decay into a single particle-hole pair, or quasiparticle decay by emission or absorption of a single real phonon. The two quasiparticle decay modes are treated on a common footing, without ad hoc separation, by accounting fully for the dynamics of the phonon propagator and the Coulomb vertex---the latter by expansion of the four-point Coulomb vertex function. The results are shown to be expressible in terms of only the physical (i.e., fully renormalized) energies and coupling constants, and are written in terms of spectral functions such as ${\ensuremath{\alpha}}^{2}$F(\ensuremath{\omega}) and its generalizations. Expansion of these in powers of a phonon linewidth parameter distinguishes (in lowest orders) between quasiparticle decay modes involving real and virtual phonons. However, the simplest prescription for calculating decay rates involves an effective scattering amplitude in which this distinction is not made.