25,247 research outputs found
The structure of the graviton self-energy at finite temperature
We study the graviton self-energy function in a general gauge, using a hard
thermal loop expansion which includes terms proportional to T^4, T^2 and
log(T). We verify explicitly the gauge independence of the leading T^4 term and
obtain a compact expression for the sub-leading T^2 contribution. It is shown
that the logarithmic term has the same structure as the ultraviolet pole part
of the T=0 self-energy function. We argue that the gauge-dependent part of the
T^2 contribution is effectively canceled in the dispersion relations of the
graviton plasma, and present the solutions of these equations.Comment: 27 pages, 6 figure
Hard Thermal Loops in the n-Dimensional phi3 Theory
We derive a closed-form result for the leading thermal contributions which
appear in the n-dimensional phi3 theory at high temperature. These
contributions become local only in the long wavelength and in the static
limits, being given by different expressions in these two limits.Comment: 3 pages, one figure. To be published in the Brazilian Journal of
Physic
Thermal instability in a gravity-like scalar theory
We study the question of stability of the ground state of a scalar theory
which is a generalization of the phi^3 theory and has some similarity to
gravity with a cosmological constant. We show that the ground state of the
theory at zero temperature becomes unstable above a certain critical
temperature, which is evaluated in closed form at high temperature.Comment: Four pages, two figures. Revised version published in the Physical
Review
Non-Quadratic Gauge Fixing and Global Gauge Invariance in the Effective Action
The possibility of having a gauge fixing term in the effective Lagrangian
that is not a quadratic expression has been explored in spin-two theories so as
to have a propagator that is both traceless and transverse. We first show how
this same approach can be used in spontaneously broken gauge theories as an
alternate to the 't Hooft gauge fixing which avoids terms quadratic in the
scalar fields. This "non-quadratic" gauge fixing in the effective action
results in there being two complex Fermionic and one real Bosonic ghost fields.
A global gauge invariance involving a Fermionic gauge parameter, analogous to
the usual BRST invariance, is present in this effective action.Comment: 4 pages, revtex4 (submitted to Phys. Rev. D
Parity-violating electromagnetic interactions in QED_3 at finite temperature
We study the parity-breaking terms generated by the box diagram in 2+1
dimensional thermal QED. These lead, in the long wave limit, to a gauge
invariant extensive action which behaves as 1/T at high temperature. In
contrast, the effective action in the static limit involves leading
non-extensive terms proportional to 1/T^3 at high temperature, which violate
large gauge invariance. We derive a non-linear large gauge Ward identity, which
relates the leading static terms of different order in perturbation theory and
whose solution coincides with the all order effective action proposed earlier.Comment: 25 pages, 3 figure
Dispersion relations for the self-energy in non-commutative field theories
We study the IR/UV connection in non-commutative theory as well as
in non-commutative QED from the point of view of the dispersion relation for
the self-energy. We show that, although the imaginary part of the self-energy
is well behaved as the parameter of non-commutativity vanishes, the real part
becomes divergent as a consequence of the high energy behavior of the
dispersion integral. Some other interesting features that arise from this
analysis are also briefly discussed.Comment: 10 page
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