4,384 research outputs found
A note on the phase transition in a topologically massive Ginzburg-Landau theory
We consider the phase transition in a model which consists of a
Ginzburg-Landau free energy for superconductors including a Chern-Simons term.
The mean field theory of Halperin, Lubensky and Ma [Phys. Rev. Lett. 32, 292
(1974)] is applied for this model. It is found that the topological mass,
, drives the system into different regimes of phase transition. For
instance, there is a such that for a
fluctuation induced first order phase transition occurs. On the other hand, for
only the second order phase transition exists. The 1-loop
renormalization group analysis gives further insight to this picture. The fixed
point structure exhibits tricritical and second order fixed points.Comment: Revised version; uses a more physical parametrization of the
renormalization group equations; new references added; one figure added;
EuroLatex, 6 page
A non-perturbative approach to the Coleman- Weinberg mechanism in massless scalar QED
We rederive non-perturbatively the Coleman-Weinberg expression for the
effective potential for massless scalar QED. Our result is not restricted to
small values of the coupling constants. This shows that the Coleman- Weinberg
result can be established beyond the range of validity of perturbation theory.
Also, we derive it in a manifestly renormalization group invariant way. It is
shown that with the derivation given no Landau ghost singularity arises. The
finite temperature case is discussed.
Pacs number: 11.10.Ef,11.10.Gh
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info:eu-repo/semantics/publishedVersio
On the Integrability and Chaos of an N=2 Maxwell-Chern-Simons-Higgs Mechanical Model
We apply different integrability analysis procedures to a reduced (spatially
homogeneous) mechanical system derived from an off-shell non-minimally coupled
N=2 Maxwell-Chern-Simons-Higgs model that presents BPS topological vortex
excitations, numerically obtained with an ansatz adopted in a special -
critical coupling - parametric regime. As a counterpart of the regularity
associated to the static soliton-like solution, we investigate the possibility
of chaotic dynamics in the evolution of the spatially homogeneous reduced
system, descendant from the full N=2 model under consideration. The originally
rich content of symmetries and interactions, N=2 susy and non-minimal coupling,
singles out the proposed model as an interesting framework for the
investigation of the role played by (super-)symmetries and parametric domains
in the triggering/control of chaotic behavior in gauge systems.
After writing down effective Lagrangian and Hamiltonian functions, and
establishing the corresponding canonical Hamilton equations, we apply global
integrability Noether point symmetries and Painleveproperty criteria to both
the general and the critical coupling regimes. As a non-integrable character is
detected by the pair of analytical criteria applied, we perform suitable
numerical simulations, as we seek for chaotic patterns in the system evolution.
Finally, we present some Comments on the results and perspectives for further
investigations and forthcoming communications.Comment: 18 pages, 5 figure
Gauge dependenceof the order parameter anomalous dimension in the Ginzburg-Landau model and the critical fluctuations in superconductors
The critical fluctuations of superconductors are discussed in a fixed
dimension scaling suited to describe the type II regime. The gauge dependence
of the anomalous dimension of the scalar field is stablished exactly from the
Ward-Takahashi identities. Its fixed point value gives the critical
exponent and it is shown that is gauge independent, as expected on
physical grounds. In the scaling considered, is found to be zero at
1-loop order, while . This result is just the 1-loop values
for the XY model obtained in the fixed dimension renormalization group
approach. It is shown that this XY behavior holds at all orders. The result
should be contrasted with the negative values frequently
reported in the literature.Comment: EuroLaTex, 7 pages, 2 figures, reference updated; version to be
published in Europhysics Letter
Spin Josephson effect in ferromagnet/ferromagnet tunnel junctions
We consider the tunnel spin current between two ferromagnetic metals from a
perspective similar to the one used in superconductor/superconductor tunnel
junctions. We use fundamental arguments to derive a Josephson-like spin tunnel
current . Here the phases are
associated with the planar contribution to the magnetization,
. The crucial step in our
analysis is the fact that the -component of the spin is canonically
conjugate to the phase of the planar contribution: . This is
analogous to the commutation relation in superconductors, where
is the phase associated to the superconducting order parameter and
is the Cooper pair number operator. We briefly discuss the experimental
consequences of our theoretical analysis.Comment: LaTex, seven pages, no figures; version to appear in Europhys. Lett.;
in order to make room for a more extended microscopic analysis, the
phenomenological discussion contained in v2 was remove
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