3,884 research outputs found
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
Techniques for n-Particle Irreducible Effective Theories
In this paper we show that the skeleton diagrams in the m-Loop nPI effective
action correspond to an infinite resummation of perturbative diagrams which is
void of double counting at the m-Loop level. We also show that the variational
equations of motion produced by the n-Loop nPI effective theory are equivalent
to the Schwinger-Dyson equations, up to the order at which they are consistent
with the underlying symmetries of the original theory. We use a diagrammatic
technique to obtain the 5-Loop 5PI effective action for a scalar theory with
cubic and quartic interactions, and verify that the result satisfies these two
statements.Comment: 43 pages, 48 figures, add a paragraph in conclusions, Figs. 25,45,46
changed, typos corrected, final version to appear in PR
Results from the 4PI Effective Action in 2- and 3-dimensions
We consider a symmetric scalar theory with quartic coupling and solve the
equations of motion from the 4PI effective action in 2- and 3-dimensions using
an iterative numerical lattice method. For coupling less than 10 (in
dimensionless units) good convergence is obtained in less than 10 iterations.
We use lattice size up to 16 in 2-dimensions and 10 in 3-dimensions and
demonstrate the convergence of the results with increasing lattice size. The
self-consistent solutions for the 2-point and 4-point functions agree well with
the perturbative ones when the coupling is small and deviate when the coupling
is large.Comment: 14 pages, 11 figures; v5: added numerical calculations in 3D; version
accepted for publication in EPJ
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
Spontaneous Symmetry Breaking for Scalar QED with Non-minimal Chern-Simons Coupling
We investigate the two-loop effective potential for both minimally and
non-minimally coupled Maxwell-Chern-Simons theories. The non-minimal gauge
interaction represents the magnetic moment interaction between a charged scalar
and the electromagnetic field. In a previous paper we have shown that the two
loop effective potential for this model is renormalizable with an appropriate
choice of the non-minimal coupling constant. We carry out a detailed analysis
of the spontaneous symmetry breaking induced by radiative corrections. As long
as the renormalization point for all couplings is chosen to be the true minimum
of the effective potential, both models predict the presence of spontaneous
symmetry breaking. Two loop corrections are small compared to the one loop
result, and thus the symmetry breaking is perturbatively stable.Comment: Revtex 25 pages, 9 figure
Temperature dependent anisotropy of the penetration depth and coherence length in MgB$_2
We report measurements of the temperature dependent anisotropies
( and ) of both the London penetration depth
and the upper critical field of MgB. Data for
was obtained from measurements of
and on a single crystal sample using a tunnel diode
oscillator technique. was
deduced from field dependent specific heat measurements on the same sample.
and have opposite temperature dependencies, but
close to tend to a common value (). These results are in good agreement with theories
accounting for the two gap nature of MgBComment: 4 pages with figures (New version
QED Electrical Conductivity using the 2PI Effective Action
In this article we calculate the electrical conductivity in QED using the 2PI
effective action. We use a modified version of the usual 2PI effective action
which is defined with respect to self-consistent solutions of the 2-point
functions. We show that the green functions obtained from this modified
effective action satisfy ward identities and that the conductivity obtained
from the kubo relation is gauge invariant. We work to 3-loop order in the
modified 2PI effective action and show explicitly that the resulting expression
for the conductivity contains the square of the amplitude that corresponds to
all binary collision and production processes.Comment: 24 pages, 21 figure
Ward Identities in Non-equilibrium QED
We verify the QED Ward identity for the two- and three -point functions at
non-equilibrium in the HTL limit. We use the Keldysh formalism of real time
finite temperature field theory. We obtain an identity of the same form as the
Ward identity for a set of one loop self-energy and one loop three-point vertex
diagrams which are constructed from HTL effective propagators and vertices.Comment: 19 pages, RevTex, 4 PostScript figures, revised version to be
published in Phys. Rev.
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