2,465 research outputs found
The heat-kernel and the average effective potential
We discuss the definition of the average effective action in terms of the
heat-kernel. As an example we examine a model describing a self-interacting
scalar field, both in flat and curved background, and study the renormalization
group flow of some of the parameters characterizing its effective potential.
Some implications of the running of these parameters for inflationary cosmology
are also briefly discussed.Comment: 9 pages, plain-Te
Gauge Invariance, the Quantum Action Principle, and the Renormalization Group
If the Wilsonian renormalization group (RG) is formulated with a cutoff that
breaks gauge invariance, then gauge invariance may be recovered only once the
cutoff is removed and only once a set of effective Ward identities is imposed.
We show that an effective Quantum Action Principle can be formulated in
perturbation theory which enables the effective Ward identities to be solved
order by order, even if the theory requires non-vanishing subtraction points.
The difficulties encountered with non-perturbative approximations are briefly
discussed.Comment: 11 pages, latex, no figures, one reference added, version to be
published on Phys. Lett.
A gauge invariant exact renormalization group I
A manifestly gauge invariant continuous renormalization group flow equation
is constructed for pure SU(N) gauge theory. The formulation makes sense without
gauge fixing and manifestly gauge invariant calculations may thus be carried
out. The flow equation is naturally expressed in terms of fluctuating Wilson
loops, with the effective action appearing as an integral over a `gas' of
Wilson loops. At infinite N, the effective action collapses to a path integral
over the trajectory of a single particle describing one Wilson loop. We show
that further regularization of these flow equations is needed. (This is
introduced in part II.)Comment: TeX, harvmac, epsf; 35 pages, 15 figs; a few typos correcte
The beta functions of a scalar theory coupled to gravity
We study a scalar field theory coupled to gravity on a flat background, below
Planck's energy. Einstein's theory is treated as an effective field theory.
Within the context of Wilson's renormalization group, we compute gravitational
corrections to the beta functions and the anomalous dimension of the scalar
field, taking into account threshold effects.Comment: 13 pages, plainTe
Exact Flow Equations and the U(1)-Problem
The effective action of a SU(N)-gauge theory coupled to fermions is evaluated
at a large infrared cut-off scale k within the path integral approach. The
gauge field measure includes topologically non-trivial configurations
(instantons). Due to the explicit infrared regularisation there are no gauge
field zero modes. The Dirac operator of instanton configurations shows a zero
mode even after the infrared regularisation, which leads to U_A(1)-violating
terms in the effective action. These terms are calculated in the limit of large
scales k.Comment: 22 pages, latex, no figures, with stylistic changes and some
arguments streamlined, typos corrected, References added, to appear in Phys.
Rev.
Periodic Instantons in SU(2) Yang-Mills-Higgs Theory
The properties of periodic instanton solutions of the classical SU(2) gauge
theory with a Higgs doublet field are described analytically at low energies,
and found numerically for all energies up to and beyond the sphaleron energy.
Interesting new classes of bifurcating complex periodic instanton solutions to
the Yang-Mills-Higgs equations are described.Comment: 11 pages, 3 figures (in 5 included eps files), ReVTeX (minor typos
corrected and reference added
Three dimensional massive scalar field theory and the derivative expansion of the renormalization group
We show that non-perturbative fixed points of the exact renormalization
group, their perturbations and corresponding massive field theories can all be
determined directly in the continuum -- without using bare actions or any
tuning procedure. As an example, we estimate the universal couplings of the
non-perturbative three-dimensional one-component massive scalar field theory in
the Ising model universality class, by using a derivative expansion (and no
other approximation). These are compared to the recent results from other
methods. At order derivative-squared approximation, the four-point coupling at
zero momentum is better determined by other methods, but factoring this out
appropriately, all our other results are in very close agreement with the most
powerful of these methods. In addition we provide for the first time, estimates
of the n-point couplings at zero momentum, with n=12,14, and the order
momentum-squared parts with n=2 ... 10.Comment: 33 pages, 1 eps figure, 7 tables; TeX + harvmac; version to appear in
Nucl. Phys.
Effective average action in statistical physics and quantum field theory
An exact renormalization group equation describes the dependence of the free
energy on an infrared cutoff for the quantum or thermal fluctuations. It
interpolates between the microphysical laws and the complex macroscopic
phenomena. We present a simple unified description of critical phenomena for
O(N)-symmetric scalar models in two, three or four dimensions, including
essential scaling for the Kosterlitz-Thouless transition.Comment: 34 pages,5 figures,LaTe
Evaluation of an automatic gas chromatographic system for the identification of bacterial infective agents
The potential clinical application of gas chromatography to
microbial identifcation was evaluated. A completely automated
system, the MIS (Microbial Identification System; Hewlett-
Packard) can analyse and identify pure strains by comparison of
their cellular fatty acids patterns (C9-C20) with the reference
parameters stored in a library. Three hundred and sixty-seven
strains were tested, comparing the gas chromatographic results
with those obtained by the traditional microbiological methods in
the bacteriology laboratory of our Institute. A standardized
extractive procedure was followed to obtain the fatty acid methyl
esters (FAMEs), but some modifications to the recommended
procedure were introduced in the bacterial growth procedures:
colonies harvested not only from the recommended growth media but
also from selective media routinely used in the bacteriology
laboratory were successfully examined. These modifications did not
influence the results but improved the ease for the user; good
agreement with the comparison method was observed as far as
identifications of genus and species are concerned for 238 cases.
The major advantages of this computerized system are a reduction
in the time required to obtain the final results, the elimination of
human errors by using the autosampler and a better inter-laboratory
comparability of results owing to a higher degree of objectivity. On
the other hand, the limited throughput of MIS (only 40 samples in
24 h) prevents its use in a large routine laboratory; this technology
is appropriate in emergency cases, in taxonomic studies and as a
confirmatory method
Non-Compact Pure Gauge QED in 3D is Free
For all Poincar\'e invariant Lagrangians of the form , in three Euclidean dimensions, where is any invariant
function of a non-compact field strength , we find that the
only continuum limit (described by just such a gauge field) is that of free
field theory: First we approximate a gauge invariant version of Wilson's
renormalization group by neglecting all higher derivative terms in , but allowing for a general non-vanishing anomalous
dimension. Then we prove analytically that the resulting flow equation has only
one acceptable fixed point: the Gaussian fixed point. The possible relevance to
high- superconductivity is briefly discussed.Comment: 11 pages, plain tex, uses harvmac. Minor additions - version to be
published in Physics Letters
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