55,619 research outputs found
Scheme Independence to all Loops
The immense freedom in the construction of Exact Renormalization Groups means
that the many non-universal details of the formalism need never be exactly
specified, instead satisfying only general constraints. In the context of a
manifestly gauge invariant Exact Renormalization Group for SU(N) Yang-Mills, we
outline a proof that, to all orders in perturbation theory, all explicit
dependence of beta function coefficients on both the seed action and details of
the covariantization cancels out. Further, we speculate that, within the
infinite number of renormalization schemes implicit within our approach, the
perturbative beta function depends only on the universal details of the setup,
to all orders.Comment: 18 pages, 8 figures; Proceedings of Renormalization Group 2005,
Helsinki, Finland, 30th August - 3 September 2005. v2: Published in jphysa;
minor changes / refinements; refs. adde
Sensitivity of Nonrenormalizable Trajectories to the Bare Scale
Working in scalar field theory, we consider RG trajectories which correspond
to nonrenormalizable theories, in the Wilsonian sense. An interesting question
to ask of such trajectories is, given some fixed starting point in parameter
space, how the effective action at the effective scale, Lambda, changes as the
bare scale (and hence the duration of the flow down to Lambda) is changed. When
the effective action satisfies Polchinski's version of the Exact
Renormalization Group equation, we prove, directly from the path integral, that
the dependence of the effective action on the bare scale, keeping the
interaction part of the bare action fixed, is given by an equation of the same
form as the Polchinski equation but with a kernel of the opposite sign. We then
investigate whether similar equations exist for various generalizations of the
Polchinski equation. Using nonperturbative, diagrammatic arguments we find that
an action can always be constructed which satisfies the Polchinski-like
equation under variation of the bare scale. For the family of flow equations in
which the field is renormalized, but the blocking functional is the simplest
allowed, this action is essentially identified with the effective action at
Lambda = 0. This does not seem to hold for more elaborate generalizations.Comment: v1: 23 pages, 5 figures, v2: intro extended, refs added, published in
jphy
Conformal anomaly from gauge fields without gauge fixing
We show how the Weyl anomaly generated by gauge fields, can be computed from
manifestly gauge invariant and diffeomorphism invariant exact renormalization
group equations, without having to fix the gauge at any stage. Regularisation
is provided by covariant higher derivatives and by embedding the Maxwell field
into a spontaneously broken supergauge theory. We first provide a
realisation that leaves behind two versions of the original gauge field,
and then construct a manifestly supergauge invariant flow equation
which leaves behind only the original Maxwell field in the spontaneously broken
regime.Comment: 24 page
Chameleon effect and the Pioneer anomaly
The possibility that the apparent anomalous acceleration of the Pioneer 10
and 11 spacecraft may be due, at least in part, to a chameleon field effect is
examined. A small spacecraft, with no thin shell, can have a more pronounced
anomalous acceleration than a large compact body, such as a planet, having a
thin shell. The chameleon effect seems to present a natural way to explain the
differences seen in deviations from pure Newtonian gravity for a spacecraft and
for a planet, and appears to be compatible with the basic features of the
Pioneer anomaly, including the appearance of a jerk term. However, estimates of
the size of the chameleon effect indicate that its contribution to the
anomalous acceleration is negligible. We conclude that any inverse-square
component in the anomalous acceleration is more likely caused by an unmodelled
reaction force from solar-radiation pressure, rather than a chameleon field
effect.Comment: 16 pages; to appear in Phys.Rev.
Minimal-resource computer program for automatic generation of ocean wave ray or crest diagrams in shoaling waters
A computer program for studying linear ocean wave refraction is described. The program features random-access modular bathymetry data storage. Three bottom topography approximation techniques are available in the program which provide varying degrees of bathymetry data smoothing. Refraction diagrams are generated automatically and can be displayed graphically in three forms: Ray patterns with specified uniform deepwater ray density, ray patterns with controlled nearshore ray density, or crest patterns constructed by using a cubic polynomial to approximate crest segments between adjacent rays
Electroconvection in a Suspended Fluid Film: A Linear Stability Analysis
A suspended fluid film with two free surfaces convects when a sufficiently
large voltage is applied across it. We present a linear stability analysis for
this system. The forces driving convection are due to the interaction of the
applied electric field with space charge which develops near the free surfaces.
Our analysis is similar to that for the two-dimensional B\'enard problem, but
with important differences due to coupling between the charge distribution and
the field. We find the neutral stability boundary of a dimensionless control
parameter as a function of the dimensionless wave number .
, which is proportional to the square of the applied voltage, is
analogous to the Rayleigh number. The critical values and
are found from the minimum of the stability boundary, and its
curvature at the minimum gives the correlation length . The
characteristic time scale , which depends on a second dimensionless
parameter , analogous to the Prandtl number, is determined from the
linear growth rate near onset. and are coefficients in the
Ginzburg-Landau amplitude equation which describes the flow pattern near onset
in this system. We compare our results to recent experiments.Comment: 36 pages, 7 included eps figures, submitted to Phys Rev E. For more
info, see http://mobydick.physics.utoronto.ca
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