977 research outputs found
The effective hyper-K"ahler potential in the N=2 supersymmetric QCD
The effective low-energy hyper-K"ahler potential for a massive N=2 matter in
the N=2 super-QCD is investigated. The N=2 extended supersymmetry severely
restricts that N=2 matter self-couplings so that their exact form can be fixed
by a few parameters, which is apparent in the N=2 harmonic superspace. In the
N=2 QED with a single matter hypermultiplet, the one-loop perturbative
calculations lead to the Taub-NUT hyper-K"ahler metric in the massive case, and
a free metric in the massless case. It is remarkable that the naive
non-renormalization `theorem' does not apply. There exists a manifestly N=2
supersymmetric duality transformation converting the low-energy effective
action for the N=2 QED hypermultiplet into a sum of the quadratic and the
improved (non-polynomial) actions for an N=2 tensor multiplet. The duality
transformation also gives a simple connection between the low-energy effective
action in the N=2 harmonic superspace and the component results.Comment: 12 pages, LaTeX, one figure and macros include
Nonlinear absorption of surface acoustic waves by composite fermions
Absorption of surface acoustic waves by a two-dimensional electron gas in a
perpendicular magnetic field is considered. The structure of such system at the
filling factor close to 1/2 can be understood as a gas of {\em composite
fermions}. It is shown that the absorption at can be strongly
nonlinear, while small deviation form 1/2 will restore the linear absorption.
Study of nonlinear absorption allows one to determine the force acting upon the
composite fermions from the acoustic wave at turning points of their
trajectories.Comment: 7 pages, 1 figure, submitted to Europhysics letter
The matreoshka of supersymmetric self-dual theories
Extended super self-dual systems have a structure reminiscent of a
``matreoshka''. For instance, solutions for N=0 are embedded in solutions for
N=1, which are in turn embedded in solutions for N=2, and so on. Consequences
of this phenomenon are explored. In particular, we present an explicit
construction of local solutions of the higher-N super self-duality equations
starting from any N=0 self-dual solution. Our construction uses N=0 solution
data to produce N=1 solution data, which in turn yields N=2 solution data, and
so on; each stage introducing a dependence of the solution on sufficiently many
additional arbitrary functions to yield the most general supersymmetric
solution having the initial N=0 solution as the helicity +1 component. The
problem of finding the general local solution of the super self-duality
equations therefore reduces to finding the general solution of the usual (N=0)
self-duality equations. Another consequence of the matreoshka phenomenon is the
vanishing of many conserved currents, including the supercurrents, for super
self-dual systems.Comment: 19 pages, Bonn-HE-93-2
Covariant Harmonic Supergraphity for N = 2 Super Yang--Mills Theories
We review the background field method for general N = 2 super Yang-Mills
theories formulated in the N = 2 harmonic superspace. The covariant harmonic
supergraph technique is then applied to rigorously prove the N=2
non-renormalization theorem as well as to compute the holomorphic low-energy
action for the N = 2 SU(2) pure super Yang-Mills theory and the leading
non-holomorphic low-energy correction for N = 4 SU(2) super Yang-Mills theory.Comment: 17 pages, LAMUPHYS LaTeX, no figures; based on talks given by I.
Buchbinder and S. Kuzenko at the International Seminar ``Supersymmetries and
Quantum Symmetries'', July 1997, Dubna; to be published in the proceeding
Point contact spectroscopy of hopping transport: effects of a magnetic field
The conductance of a point contact between two hopping insulators is expected
to be dominated by the individual localized states in its vicinity. Here we
study the additional effects due to an external magnetic field. Combined with
the measured conductance, the measured magnetoresistance provides detailed
information on these states (e.g. their localization length, the energy
difference and the hopping distance between them). We also calculate the
statistics of this magnetoresistance, which can be collected by changing the
gate voltage in a single device. Since the conductance is dominated by the
quantum interference of particular mesoscopic structures near the point
contact, it is predicted to exhibit Aharonov-Bohm oscillations, which yield
information on the geometry of these structures. These oscillations also depend
on local spin accumulation and correlations, which can be modified by the
external field. Finally, we also estimate the mesoscopic Hall voltage due to
these structures.Comment: 7 pages, 5 figur
Exact asymptotic behavior of magnetic stripe domain arrays
The classical problem of magnetic stripe domain behavior in films and plates
with uniaxial magnetic anisotropy is treated. Exact analytical results are
derived for the stripe domain widths as function of applied perpendicular
field, , in the regime where the domain period becomes large. The stripe
period diverges as , where is the critical (infinite
period) field, an exact result confirming a previous conjecture. The
magnetization approaches saturation as , a behavior which
compares excellently with experimental data obtained for a m thick
ferrite garnet film. The exact analytical solution provides a new basis for
precise characterization of uniaxial magnetic films and plates, illustrated by
a simple way to measure the domain wall energy. The mathematical approach is
applicable for similar analysis of a wide class of systems with competing
interactions where a stripe domain phase is formed.Comment: 4 pages, 4 figure
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