454 research outputs found
A Massive Renormalizable Abelian Gauge Theory in 2+1 Dimensions
The standard formulation of a massive Abelian vector field in
dimensions involves a Maxwell kinetic term plus a Chern-Simons mass term; in
its place we consider a Chern-Simons kinetic term plus a Stuekelberg mass term.
In this latter model, we still have a massive vector field, but now the
interaction with a charged spinor field is renormalizable (as opposed to super
renormalizable). By choosing an appropriate gauge fixing term, the Stuekelberg
auxiliary scalar field decouples from the vector field. The one-loop spinor
self energy is computed using operator regularization, a technique which
respects the three dimensional character of the antisymmetric tensor
. This method is used to evaluate the vector self
energy to two-loop order; it is found to vanish showing that the beta function
is zero to two-loop order. The canonical structure of the model is examined
using the Dirac constraint formalism.Comment: LaTeX, 17 pages, expanded reference list and discussion of
relationship to previous wor
Optimal Renormalization-Group Improvement of R(s) via the Method of Characteristics
We discuss the application of the method of characteristics to the
renormalization-group equation for the perturbative QCD series within the
electron-positron annihilation cross-section. We demonstrate how one such
renormalization-group improvement of this series is equivalent to a closed-form
summation of the first four towers of renormalization-group accessible
logarithms to all orders of perturbation theory
Measurement of the electron electric dipole moment using GdIG
A new method for the detection of the electron edm using a solid is
described. The method involves the measurement of a voltage induced across the
solid by the alignment of the samples magnetic dipoles in an applied magnetic
field, H. A first application of the method to GdIG has resulted in a limit on
the electron edm of 5E-24 e-cm, which is a factor of 40 below the limit
obtained from the only previous solid-state edm experiment. The result is
limited by the imperfect discrimination of an unexpectedly large voltage that
is even upon the reversal of the sample magnetization.Comment: 10 pages, 5 figures, v2:references corrected, submitted to PRL,
v3:added labels to figure
Dynamical Breakdown of Symmetry in a (2+1) Dimensional Model Containing the Chern-Simons Field
We study the vacuum stability of a model of massless scalar and fermionic
fields minimally coupled to a Chern-Simons field. The classical Lagrangian only
involves dimensionless parameters, and the model can be thought as a (2+1)
dimensional analog of the Coleman-Weinberg model. By calculating the effective
potential, we show that dynamical symmetry breakdown occurs in the two-loop
approximation. The vacuum becomes asymmetric and mass generation, for the boson
and fermion fields takes place. Renormalization group arguments are used to
clarify some aspects of the solution.Comment: Minor modifications in the text and figure
Non-Trivial Ghosts and Second Class Constraints
In a model in which a vector gauge field is coupled to an
antisymmetric tensor field possessing a pseudoscalar mass, it
has been shown that all physical degrees of freedom reside in the vector field.
Upon quantizing this model using the Faddeev-Popov procedure, explicit
calculation of the two-point functions at one-loop
order seems to have yielded the puzzling result that the effective action
generated by radiative effects has more physical degrees of freedom than the
original classical action. In this paper we point out that this is not in fact
a real effect, but rather appears to be a consequence of having ignored a
"ghost" field arising from the contribution to the measure in the path integral
arising from the presence of non-trivial second-class constraints. These ghost
fields couple to the fields and , which makes them
distinct from other models involving ghosts arising from second-class
constraints (such as massive Yang-Mills (YM) models) that have been considered,
as in these other models such ghosts decouple. As an alternative to dealing
with second class constraints, we consider introducing a "Stueckelberg field"
to eliminate second-class constraints in favour of first-class constraints and
examine if it is possible to then use the Faddeev-Popov quantization procedure.
In the Proca model, introduction of the Stueckelberg vector is equivalent to
the Batalin-Fradkin-Tyutin (BFT) approach to converting second-class
constraints to being first class through the introduction of new variables.
However, introduction of a Stueckelberg vector is not equivalent to the BFT
approach for the vector-tensor model. In an appendix, the BFT procedure is
applied to the pure tensor model and a novel gauge invariance is found.Comment: 23 pages, LaTeX2e forma
Covariant Gauge Fixing and Canonical Quantization
Theories that contain first class constraints possess gauge invariance which
results in the necessity of altering the measure in the associated quantum
mechanical path integral. If the path integral is derived from the canonical
structure of the theory, then the choice of gauge conditions used in
constructing Faddeev's measure cannot be covariant. This shortcoming is
normally overcome either by using the "Faddeev-Popov" quantization procedure,
or by the approach of Batalin-Fradkin-Fradkina-Vilkovisky, and then
demonstrating that these approaches are equivalent to the path integral
constructed from the canonical approach with Faddeev's measure. We propose in
this paper an alternate way of defining the measure for the path integral when
it is constructed using the canonical procedure for theories containing first
class constraints and that this new approach can be used in conjunction with
covariant gauges. This procedure follows the Faddeev-Popov approach, but rather
than working with the form of the gauge transformation in configuration space,
it employs the generator of the gauge transformation in phase space. We
demonstrate this approach to the path integral by applying it to Yang-Mills
theory, a spin-two field and the first order Einstein-Hilbert action in two
dimensions. The problems associated with defining the measure for theories
containing second-class constraints and ones in which there are fewer secondary
first class constraints than primary first class constraints are discussed.Comment: 31 page
The Gross-Neveu Model and the Supersymmetric and Non-Supersymmetric Nambu-Jona-Lasinio Model in a Magnetic Field
The infrared dynamics in the (3+1)-dimensional supersymmetric and
non-supersymmetric Nambu-Jona-Lasinio model in a constant magnetic field is
studied. While at strong coupling the dynamics in these two models is
essentially different, it is shown that the models become equivalent at weak
coupling. In particular, at weak coupling, as the strength of the magnetic
field goes to infinity, both the supersymmetric and non-supersymmetric
Nambu-Jona-Lasinio models are reduced to a continuum set of independent
(1+1)-dimensional Gross-Neveu models, labeled by the coordinates in the plane
perpendicular to the magnetic field. The relevance of these results for
cosmological models based on supersymmetric dynamics is pointed out.Comment: ReVTeX file, 14 pages including 1 figure. The final version that was
published in Phys.Re
Aspects of Quantum Gravity in de Sitter Spaces
In these lectures we give a review of recent attempts to understand quantum
gravity on de Sitter spaces. In particular, we discuss the holographic
correspondence between de Sitter gravity and conformal field theories proposed
by Hull and by Strominger, and how this may be reconciled with the
finite-dimensional Hilbert space proposal by Banks and Fischler. Furthermore we
review the no-go theorems that forbid an embedding of de Sitter spaces in
string theory, and discuss how they can be circumvented. Finally, some curious
issues concerning the thermal nature of de Sitter space are elucidated.Comment: 36+1 pages, 5 Postscript figures, introduction and section 6
extended, further references, final version to appear in JCA
Extrinsic and intrinsic determinants of nerve regeneration
After central nervous system (CNS) injury axons fail to regenerate often leading to persistent neurologic deficit although injured peripheral nervous system (PNS) axons mount a robust regenerative response that may lead to functional recovery. Some of the failures of CNS regeneration arise from the many glial-based inhibitory molecules found in the injured CNS, whereas the intrinsic regenerative potential of some CNS neurons is actively curtailed during CNS maturation and limited after injury. In this review, the molecular basis for extrinsic and intrinsic modulation of axon regeneration within the nervous system is evaluated. A more complete understanding of the factors limiting axonal regeneration will provide a rational basis, which is used to develop improved treatments for nervous system injury
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