54493955
Quantum statistical correlations in thermal field theories: Boundary effective theory
We show that the one-loop effective action at finite temperature for a scalar field with quartic interaction has the same renormalized expression as at zero temperature if written in terms of a certain classical field {phi}{sub c}, and if we trade free propagators at zero temperature for their finite-temperature counterparts. The result follows if we write the partition function as an integral over field eigenstates (boundary fields) of the density matrix element in the functional Schroedinger field representation, and perform a semiclassical expansion in two steps: first, we integrate around the saddle point for fixed boundary fields, which is the classical field {phi}{sub c}, a functional of the boundary fields; then, we perform a saddle-point integration over the boundary fields, whose correlations characterize the thermal properties of the system. This procedure provides a dimensionally reduced effective theory for the thermal system. We calculate the two-point correlation as an example.
43000553
Multiparticle tree amplitudes in scalar field theory.
Following an argument advanced by Feynman, we consider a method for obtaining the effective action which generates the sum of tree diagrams with external physical particles. This technique is applied, in the unbroken \ensuremath{\lambda}${\mathrm{\ensuremath{\varphi}}}^{4}$ theory, to the derivation of the threshold amplitude for the production of n scalar particles by n initial particles. The leading contributions to the tree amplitude, which become singular in the threshold limit, exhibit a factorial growth with n. \textcopyright{} 1996 The Physical Society.
119048914
The Static effective action for noncommutative QED at high temperature
In this paper, we systematically study the effective action for non-commutative QED in the static limit at high temperature. When $\theta p^{2}\ll 1$, where $\theta$ represents the magnitude of the parameter for non-commutativity and $p$ denotes a typical external three momentum, we show that this leads naturally to a derivative expansion in this model. The study of the self-energy, in this limit, leads to nontrivial $\theta$ dependent corrections to the electric and magnetic masses, which exist only above a certain critical temperature. The three point and the four point amplitudes are also studied as well as their relations to the Ward identities in this limit. We determine the closed form expression for the current involving only the spatial components of the gauge field and present the corresponding static effective action, which is gauge invariant.
44515091
Thermal Operator Representation of Finite Temperature Graphs II
F. T. Brandt, Ashok Das, Olivier Espinosa, J. Frenkel and Silvana Perez a Instituto de F́ısica, Universidade de São Paulo, São Paulo, BRAZIL b Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627-0171, USA c Departamento de F́ısica, Universidad Técnica Federico Santa Maŕıa, Casilla 110-V, Valparáıso, CHILE and d Departamento de F́ısica, Universidade Federal do Pará, Belém, Pará 66075-110, BRAZIL
119875841
Cancellation of soft interactions with spectators in the Drell-Yan process
Abstract We verify by explicit calculation, to 2-loop order, the cancellation of soft interactions with spectators in the Drell-Yan process. We employ a model in which a “meson” consists of a parton and a spectator parton, each moving along parallel eikonal lines. The process occurs in the collision of two such “mesons” at velocities near the speed of light. The calculation is sensitive to gluons with wavelengths of the order of or greater than the meson size.
35897734
Nonlinear couplings and tree amplitudes in gauge theories.
Following a remark advanced by Feynman, we study the connection between the form of the nonlinear vertices involving gauge particles and the Abelian gauge invariance of physical tree amplitudes. We show that this requirement, together with some natural assumptions, fixes uniquely the structure of the Yang-Mills theory. However, the constraints immposed by the above property are not sufficient to single out the gauge theory of gravitation. {copyright} {ital 1996 The American Physical Society.}
14262176
Global symmetries in the antifield formalism
In this paper, two things are done. First, it is shown that any global symmetry of a gauge-invariant theory can be extended to the ghosts and the antifields so as to leave invariant the solution of the master equation (before gauge fixing). Second, it is proved that the incorporation of the rigid symmetries to the solution of the master equation through the introduction of a constant ghost for each global symmetry can be obstructed already at the classical level whenever the theory possesses higher order conservation laws. Explicit examples are given.
17042364
Conserved currents and gauge invariance in Yang-Mills theory
It is shown that in the absence of free abelian gauge fields, the conserved currents of (classical) Yang-Mills gauge models coupled to matter fields can be always redefined so as to be gauge invariant. This is a direct consequence of the general analysis of the Wess-Zumino consistency condition for Yang-Mills theory that we have provided recently.
11443934
Local BRST cohomology in the antifield formalism: II. Application to Yang-Mills theory
Yang-Mills models with compact gauge group coupled to matter fields are considered. The general tools developed in a companion paper are applied to compute the local cohomology of the BRST differentials modulo the exterior space-time derivatived for all values of the ghost number, in the space of polynomials in the fields, the ghosts, the antifields (=sources for the BRST variations) and their derivatives. New solutions to the consistency conditionssa+db=0 depending non-trivially on the antifields are exhibited. For a semi-simple gauge group, however, these new solutions arise only at ghost number two or higher. Thus at ghost number zero or one, the inclusion of the antifields does not bring in new solutions to the consistency conditionsa+db=0 besides the already known ones. The analysis does not use power counting and is purely cohomological. It can be easily extended to more general actions containing higher derivatives of the curvature or Chern-Simons terms.
14272321
Local BRST Cohomology and Covariance

Abstract:The paper provides a framework for a systematic analysis of the local BRST cohomology in a large class of gauge theories. The approach is based on the cohomology of s+d in the jet space of fields and antifields, s and d being the BRST operator and exterior derivative respectively. It relates the BRST cohomology to an underlying gauge covariant algebra and reduces its computation to a compactly formulated problem involving only suitably defined generalized connections and tensor fields. The latter are shown to provide the building blocks of physically relevant quantities such as gauge invariant actions, Noether currents and gauge anomalies, as well as of the equations of motion.
115177706
Supersymmetry algebra cohomology. II. Primitive elements in 2 and 3 dimensions
The primitive elements of the supersymmetry algebra cohomology as defined in a companion paper are computed exhaustively for standard supersymmetry algebras in dimensions D = 2 and D = 3, for all signatures (t, D − t) and all numbers N of sets of supersymmetries.