279 research outputs found
QED symmetries in real-time thermal field theory
We study the discrete and gauge symmetries of Quantum Electrodynamics at
finite temperature within the real-time formalism.
The gauge invariance of the complete generating functional leads to the
finite temperature Ward identities. These Ward identities relate the eight
vertex functions to the elements of the self-energy matrix. Combining the
relations obtained from the and the gauge symmetries of the theory we
find that only one out of eight longitudinal vertex functions is independent.
As a consequence of the Ward identities it is shown that some elements of the
vertex function are singular when the photon momentum goes to zero.Comment: New version as it will appear in Phys RevD 19 pages, RevTex, 1figur
An operator representation for Matsubara sums
In the context of the imaginary-time formalism for a scalar thermal field
theory, it is shown that the result of performing the sums over Matsubara
frequencies associated with loop Feynman diagrams can be written, for some
classes of diagrams, in terms of the action of a simple linear operator on the
corresponding energy integrals of the Euclidean theory at T=0. In its simplest
form the referred operator depends only on the number of internal propagators
of the graph.
More precisely, it is shown explicitly that this \emph{thermal operator
representation} holds for two generic classes of diagrams, namely, the
two-vertex diagram with an arbitrary number of internal propagators, and the
one-loop diagram with an arbitrary number of vertices.
The validity of the thermal operator representation for diagrams of more
complicated topologies remains an open problem. Its correctness is shown to be
equivalent to the correctness of some diagrammatic rules proposed a few years
ago.Comment: 4 figures; references added, minor changes in notation, final version
accepted for publicatio
Identity of the imaginary-time and real-time thermal propagators for scalar bound states in a one-generation Nambu-Jona-Lasinio model
By rigorous reanalysis of the results, we have proven that the propagators at
finite temperature for scalar bound states in one-generation fermion condensate
scheme of electroweak symmetry breaking are in fact identical in the
imaginary-time and the real-time formalism. This dismisses the doubt about
possible discrepancy between the two formalisms in this problem. Identity of
the derived thermal transformation matrices of the real-time matrix propagators
for scalar bound states without and with chemical potential and the ones for
corresponding elementary scalar particles shows similarity of thermodynamic
property between the two types of particles. Only one former inference is
modified, i.e. when the two flavors of fermions have unequal nonzero masses,
the amplitude of the composite Higgs particle will decay instead grow in time.Comment: 5 pages, revtex4, no figure
Real-time propagators at finite temperature and chemical potential
We derive a form of spectral representations for all bosonic and fermionic
propagators in the real-time formulation of field theory at finite temperature
and chemical potential. Besides being simple and symmetrical between the
bosonic and the fermionic types, these representations depend explicitly on
analytic functions only. This last property allows a simple evaluation of loop
integrals in the energy variables over propagators in this form, even in
presence of chemical potentials, which is not possible over their conventional
form
Next-to-leading Order Debye Mass for the Quark-gluon Plasma
The Debye screening mass for a quark-gluon plasma at high temperature is
calculated to next-to-leading order in the QCD coupling constant from the
correlator of two Polyakov loops. The result agrees with the screening mass
defined by the location of the pole in the gluon propagator as calculated by
Rebhan. It is logarithmically sensitive to nonperturbative effects associated
with the screening of static chromomagnetic fields.Comment: 8 pages, NUHEP-TH-94-1
Energy Flow in Acoustic Black Holes
We present the results of an analysis of superradiant energy flow due to
scalar fields incident on an acoustic black hole. In addition to providing
independent confirmation of the recent results in [5], we determine in detail
the profile of energy flow everywhere outside the horizon. We confirm
explicitly that in a suitable frame the energy flow is inward at the horizon
and outward at infinity, as expected on physical grounds.Comment: 8 pages, 9 figures, Comments added to discussion of energy flow and
introductory section abbreviate
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