Electromagnetic Field in Some Anisotropic Stiff Fluid Universes

The electromagnetic field is studied in a family of exact solutions of the Einstein equations whose material content is a perfect fluid with stiff equation of state (p = $\epsilon$ ). The field equations are solved exactly for several members of the family.Comment: 6 pages, REVTEX,no figure

Cosmic Strings from N=2, D=5 Supergravity

Exact solutions of N=2 supergravity in five dimensions are found in the metric with cylindrical symmetry, a particular case corresponds to the exterior of a cosmic string.Comment: 5 pages, plain LATEX,no figure

Path-ordered Phase Factors in Scalar Quantum Electrodynamics

Starting from linear equations for the complex scalar field, the two- and three-point Green's functions are obtained in the infrared approximation. We show that the infrared singularity factorizes in the vertex function as in spinorial QED, reproducing in a straightforward way the result of lenghty perturbative calculations.Comment: 11 pages, LaTe

What's Wrong with Pauli-Villars Regularization in QED3QED_{3} ?

In this letter we argue that there is no ambiguity between the Pauli-Villars and other methods of regularization in (2+1)-dimensional quantum electrodynamics with respect to dynamical mass generation, provided we properly choose the couplings for the regulators.Comment: 07 pages, Latex, no figure

The Causal Phase in QED3QED_{3}

The operator ${\bf S}$ in Fock space which describes the scattering and particle production processes in an external time-dependent electromagnetic potential $A$ can be constructed from the one-particle S-matrix up to a physical phase $\lambda [A]$. In this work we determine this phase for $QED$ in (2+1) dimensions, by means of causality, and show that no ultraviolet divergences arise, in contrast to the usual formalism of $QED$.Comment: LaTex, 11 pages, no figure

Causal Theory for the Gauged Thirring Model

We consider the (2+1)-dimensional massive Thirring model as a gauge theory, with one fermion flavor, in the framework of the causal perturbation theory and address the problem of dynamical mass generation for the gauge boson. In this context we get an unambiguous expression for the coefficient of the induced Chern-Simons term.Comment: LaTex, 21 pages, no figure

Radiative Corrections for the Gauged Thirring Model in Causal Perturbation Theory

We evaluate the one-loop fermion self-energy for the gauged Thirring model in (2+1) dimensions, with one massive fermion flavor, in the framework of the causal perturbation theory. In contrast to QED$_3$, the corresponding two-point function turns out to be infrared finite on the mass shell. Then, by means of a Ward identity, we derive the on-shell vertex correction and discuss the role played by causality for nonrenormalizable theories.Comment: LaTex, 09 pages, no figures. Title changed and introduction enlarged. To be published in Eur. Phys. J.