1,110 research outputs found
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
The influence of measurement error on Maxwell's demon
In any general cycle of measurement, feedback and erasure, the measurement
will reduce the entropy of the system when information about the state is
obtained, while erasure, according to Landauer's principle, is accompanied by a
corresponding increase in entropy due to the compression of logical and
physical phase space. The total process can in principle be fully reversible. A
measurement error reduces the information obtained and the entropy decrease in
the system. The erasure still gives the same increase in entropy and the total
process is irreversible. Another consequence of measurement error is that a bad
feedback is applied, which further increases the entropy production if the
proper protocol adapted to the expected error rate is not applied. We consider
the effect of measurement error on a realistic single-electron box Szilard
engine. We find the optimal protocol for the cycle as a function of the desired
power and error , as well as the existence of a maximal power
.Comment: 5 pages, 4 figure
Relating harmonic and projective descriptions of N=2 nonlinear sigma models
Recent papers have established the relationship between projective superspace
and a complexified version of harmonic superspace. We extend this construction
to the case of general nonlinear sigma models in both frameworks. Using an
analogy with Hamiltonian mechanics, we demonstrate how the Hamiltonian
structure of the harmonic action and the symplectic structure of the projective
action naturally arise from a single unifying action on a complexified version
of harmonic superspace. This links the harmonic and projective descriptions of
hyperkahler target spaces. For the two examples of Taub-NUT and Eguchi-Hanson,
we show how to derive the projective superspace solutions from the harmonic
superspace solutions.Comment: 25 pages; v3: typo fixed in eq (1.36
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
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
On Projective Hoops: Loops in Hyperspace
We (re)derive the propagators and Feynman rules for the massless scalar and
vector multiplets in N=2 Projective Superspace ('Projective Hyperspace'). With
these, we are able to calculate both the divergent and finite parts of 2, 3 &
4-point functions at 1-loop for N=2 Super-Yang-Mills theory (SYM) explicitly in
Projective Hyperspace itself. We find that effectively only the coupling
constant needs to be renormalized unlike in the N=1 case where an independent
wavefunction renormalization is also required. This feature is similar to that
of the background field gauge, even though we are using ordinary Fermi-Feynman
gauge. The computation of 1-hoop beta-function is then straightforward and
matches with the known result. We also show that it receives no 2-hoops
contributions. All these calculations provide an alternative proof of the
finiteness of N=4 SYM.Comment: 29 pages, 12 figures; Added a reference & modified introduction in v
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