1,145 research outputs found
SELF-DUAL SUPERGRAVITIES
The N-extended supersymmetric self-dual Poincar\'e supergravity equations
provide a natural local description of supermanifolds possessing hyperk\"ahler
structure. These equations admit an economical formulation in chiral
superspace. A reformulation in harmonic superspace encodes self-dual
supervielbeins and superconnections in a graded skew-symmetric supermatrix
superfield prepotential satisfying generalised Cauchy-Riemann conditions. A
recipe is presented for extracting explicit self-dual supervielbeins and
superconnections from such `analytic' prepotentials. We demonstrate the method
by explicitly decoding a simple example of superfield prepotential, analogous
to that corresponding to the Taub-NUT solution. The superspace we thus
construct is an interesting supersymmetric deformation of flat space,
having flat `body' and constant curvature `soul'.Comment: 14 pages, latex fil
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
N=4, 3D Supersymmetric Quantum Mechanics in Non-Abelian Monopole Background
Using the harmonic superspace approach, we construct the three-dimensional
N=4 supersymmetric quantum mechanics of the supermultiplet (3,4,1) coupled to
an external SU(2) gauge field. The off-shell N=4 supersymmetry requires the
gauge field to be a static form of the 't Hooft ansatz for the 4D self-dual
SU(2) gauge fields, that is a particular solution of Bogomolny equations for
BPS monopoles. We present the explicit form of the corresponding superfield and
component actions, as well as of the quantum Hamiltonian and N=4 supercharges.
The latter can be used to describe a more general N=4 mechanics system, with an
arbitrary BPS monopole background and on-shell N=4 supersymmetry. The essential
feature of our construction is the use of semi-dynamical spin (4,4,0) multiplet
with the Wess-Zumino type action.Comment: 16 pages, reference added, published versio
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
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