2,767 research outputs found
Leading Order QED Electrical Conductivity from the 3PI Effective Action
In this article we study the electrical conductivity in QED using the
resummed 3PI effective action. We work to 3-loop order in the effective action.
We show that the resulting expression for the conductivity is explicitly gauge
invariant, and that the integral equations that resum the pinching and colinear
contributions are produced naturally by the formalism. All leading order terms
are included, without the need for any kind of power counting arguments.Comment: 10 pages, 15 figure
Three-Point Functions at Finite Temperature
We study 3-point functions at finite temperature in the closed time path
formalism. We give a general decomposition of the eight component tensor in
terms of seven vertex functions. We derive a spectral representation for these
seven functions in terms of two independent real spectral functions. We derive
relationships between the seven functions and obtain a representation of the
vertex tensor that greatly simplifies calculations in real time.Comment: 21 pages LaTeX; one ps-figure; Revised version, contains more
references and discussio
Next-to-Leading Order Transport Coefficients from the Four-Particle Irreducible Effective Action
Transport coefficients can be obtained from 2-point correlators using the
Kubo formulae. It has been shown that the full leading order result for
electrical conductivity and (QCD) shear viscosity is contained in the re-summed
2-point function that is obtained from the 3-loop 3PI re-summed effective
action. The theory produces all leading order contributions without the
necessity for power counting, and in this sense it provides a natural framework
for the calculation. In this article we study the 4-loop 4PI effective action
for a scalar theory with cubic and quartic interactions in the presence of
spontaneous symmetry breaking. We obtain a set of integral equations that
determine the re-summed 2-point vertex function. A next-to-leading order
contribution to the viscosity could be obtained from this set of coupled
equations.Comment: 24 pages, 18 figures. Added references and minor rewordings:
published versio
The soft fermion dispersion relation at next-to-leading order in hot QED
We study next-to-leading order contributions to the soft static fermion
dispersion relation in hot QED. We derive an expression for the complete
next-to-leading order contribution to the retarded fermion self-energy. The
real and imaginary parts of this expression give the next-to-leading order
contributions to the mass and damping rate of the fermionic quasi-particle.
Many of the terms that are expected to contribute according to the traditional
power counting argument are actually subleading. We explain why the power
counting method over estimates the contribution from these terms. For the
electron damping rate in QED we obtain: . We check our method by calculating the next-to-leading order
contribution to the damping rate for the case of QCD with two flavours and
three coulours. Our result agrees with the result obtained previously in the
literature. The numerical evaluation of the nlo contribution to the mass is
left to a future publication.Comment: 15 pages, 5 figure
KMS conditions for 4-point Green functions at finite temperature
We study the 4-point function in the Keldysh formalism of the closed time
path formulation of real time finite temperature field theory.
We derive the KMS conditions for these functions and discuss the number of
4-point functions that are independent. We define a set of `physical' functions
which are linear combinations of the usual Keldysh functions. We show that
these functions satisfy simple KMS conditions. In addition, we consider a set
of integral equations which represent a resummation of ladder graphs. We show
that these integral equations decouple when one uses the physical functions
that we have defined. We discuss the generalization of these results to QED.Comment: 17 pages in Revtex with 2 figure
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