209 research outputs found
On General Axial Gauges for QCD
General Axial Gauges within a perturbative approach to QCD are plagued by
'spurious' propagator singularities. Their regularisation has to face major
conceptual and technical problems. We show that this obstacle is naturally
absent within a Wilsonian or 'Exact' Renormalisation Group approach and explain
why this is so. The axial gauge turns out to be a fixed point under the flow,
and the universal 1-loop running of the gauge coupling is computed.Comment: 4 pages, latex, talk presented by DFL at QCD'98, Montpellier, July
2-8, 1998; to be published in Nucl. Phys. B (Proc. Suppl.
Thermal one- and two-graviton Green's functions in the temporal gauge
The thermal one- and two-graviton Green's function are computed using a
temporal gauge. In order to handle the extra poles which are present in the
propagator, we employ an ambiguity-free technique in the imaginary-time
formalism. For temperatures T high compared with the external momentum, we
obtain the leading T^4 as well as the subleading T^2 and log(T) contributions
to the graviton self-energy. The gauge fixing independence of the leading T^4
terms as well as the Ward identity relating the self-energy with the one-point
function are explicitly verified. We also verify the 't Hooft identities for
the subleading T^2 terms and show that the logarithmic part has the same
structure as the residue of the ultraviolet pole of the zero temperature
graviton self-energy. We explicitly compute the extra terms generated by the
prescription poles and verify that they do not change the behavior of the
leading and sub-leading contributions from the hard thermal loop region. We
discuss the modification of the solutions of the dispersion relations in the
graviton plasma induced by the subleading T^2 contributions.Comment: 17 pages, 5 figures. Revised version to be published in Phys. Rev.
The 3-graviton vertex function in thermal quantum gravity
The high temperature limit of the 3-graviton vertex function is studied in
thermal quantum gravity, to one loop order. The leading () contributions
arising from internal gravitons are calculated and shown to be twice the ones
associated with internal scalar particles, in correspondence with the two
helicity states of the graviton. The gauge invariance of this result follows in
consequence of the Ward and Weyl identities obeyed by the thermal loops, which
are verified explicitly.Comment: 19 pages, plain TeX, IFUSP/P-100
Chern-Simons as a geometrical set up for three dimensional gauge theories
Three dimensional Yang-Mills gauge theories in the presence of the
Chern-Simons action are seen as being generated by the pure topological
Chern-Simons term through nonlinear covariant redefinitions of the gauge fieldComment: 26 pages, latex2
LC_2 formulation of supergravity
We formulate (N=1, d=11) supergravity in components in light-cone gauge
(LC_2) to order . In this formulation, we use judicious gauge choices
and the associated constraint relations to express the metric, three-form and
gravitino entirely in terms of the physical degrees of freedom in the theory.Comment: 11 page
A Generalization of Slavnov-Extended Non-Commutative Gauge Theories
We consider a non-commutative U(1) gauge theory in 4 dimensions with a
modified Slavnov term which looks similar to the 3-dimensional BF model. In
choosing a space-like axial gauge fixing we find a new vector supersymmetry
which is used to show that the model is free of UV/IR mixing problems, just as
in the previously discussed model in arXiv:hep-th/0604154. Finally, we present
generalizations of our proposed model to higher dimensions.Comment: 25 pages, no figures; v2 minor correction
Similarity Renormalization, Hamiltonian Flow Equations, and Dyson's Intermediate Representation
A general framework is presented for the renormalization of Hamiltonians via
a similarity transformation. Divergences in the similarity flow equations may
be handled with dimensional regularization in this approach, and the resulting
effective Hamiltonian is finite since states well-separated in energy are
uncoupled. Specific schemes developed several years ago by Glazek and Wilson
and contemporaneously by Wegner correspond to particular choices within this
framework, and the relative merits of such choices are discussed from this
vantage point. It is shown that a scheme for the transformation of Hamiltonians
introduced by Dyson in the early 1950's also corresponds to a particular choice
within the similarity renormalization framework, and it is argued that Dyson's
scheme is preferable to the others for ease of computation. As an example, it
is shown how a logarithmically confining potential arises simply at second
order in light-front QCD within Dyson's scheme, a result found previously for
other similarity renormalization schemes. Steps toward higher order and
nonperturbative calculations are outlined. In particular, a set of equations
analogous to Dyson-Schwinger equations is developed.Comment: REVTex, 32 pages, 7 figures (corrected references
Wilson loops in the adjoint representation and multiple vacua in two-dimensional Yang-Mills theory
with fermions in the adjoint representation is invariant under
and thereby is endowed with a non-trivial vacuum structure
(k-sectors). The static potential between adjoint charges, in the limit of
infinite mass, can be therefore obtained by computing Wilson loops in the pure
Yang-Mills theory with the same non-trivial structure. When the (Euclidean)
space-time is compactified on a sphere , Wilson loops can be exactly
expressed in terms of an infinite series of topological excitations
(instantons). The presence of k-sectors modifies the energy spectrum of the
theory and its instanton content. For the exact solution, in the limit in which
the sphere is decompactified, a k-sector can be mimicked by the presence of
k-fundamental charges at , according to a Witten's suggestion. However
this property neither holds before decompactification nor for the genuine
perturbative solution which corresponds to the zero-instanton contribution on
.Comment: RevTeX, 46 pages, 1 eps-figur
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