1,195 research outputs found
Superconformal spaces and implications for superstrings
We clarify some properties of projective superspace by using a manifestly
superconformal notation. In particular, we analyze the N=2 scalar multiplet in
detail, including its action, and the propagator and its super-Schwinger
parameters. The internal symmetry is taken to be noncompact (after Wick
rotation), allowing boundary conditions that preserve it off shell.
Generalization to N=4 suggests the coset superspace PSU(2,2|4)/OSp(4|4) for the
AdS/CFT superstring.Comment: 19 pages, no figures; v2: fixed sign, added note & reference; v3:
added note & references, version to appear in Physical Review
Supersymmetric sigma models and the 't Hooft instantons
Witten's linear sigma model for ADHM instantons possesses a natural
supersymmetry. We study generalizations of the infrared limit of the model that
are invariant under supersymmetry. In the case of four space-time
dimensions a background with a conformally flat metric and torsion is required.
The geometry is specified by a single real scalar function satisfying Laplace's
equation. It gives rise to 't Hooft instantons for the gauge group ,
instead of the general ADHM instantons for an gauge group in the case
.Comment: 11 pages, Latex fil
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
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
Constrained superpotentials in harmonic gauge theories with 8 supercharges
We consider D-dimensional supersymmetric gauge theories with 8 supercharges
(D<6,) in the framework of harmonic superspaces. The effective
Abelian low-energy action for D=5 contains the free and Chern-Simons terms.
Effective superfield actions for D<4 can be written in terms of
the superpotentials satisfying the superfield constraints and (6-D)-dimensional
Laplace equations. The role of alternative harmonic structures is discussed.Comment: LATEX file, 9 pages, version published in Teor. Mat. Fi
Conformally coupled supermultiplets in four and five dimensions
We obtain by superfield methods the exceptional representations of the
OSp(2N/4,R) and SU(2,2/1) superalgebras which extend to supersingletons of
SU(2,2/2N) and F(4), respectively. These representations describe
superconformally coupled multiplets and appear in three- and four-dimensional
superconformal field theories which are holographic descriptions of certain
anti-de Sitter supergravities
Observation and analysis of Fano-like lineshapes in the Raman spectra of molecules adsorbed at metal interfaces
Surface enhanced Raman spectra from molecules (bipyridyl ethylene) adsorbed
on gold dumbells are observed to become increasingly asymmetric (Fano-like) at
higher incident light intensity. The electronic temperature (inferred from the
anti-Stokes (AS) electronic Raman signal increases at the same time while no
vibrational AS scattering is seen. These observations are analyzed by assuming
that the molecule-metal coupling contains an intensity dependent contribution
(resulting from light-induced charge transfer transitions as well as
renormalization of the molecule metal tunneling barrier). We find that
interference between vibrational and electronic inelastic scattering routes is
possible in the presence of strong enough electron-vibrational coupling and can
in principle lead to the observed Fano-like feature in the Raman scattering
profile. However the best fit to the observed results, including the dependence
on incident light intensity and the associated thermal response is obtained
from a model that disregards this coupling and accounts for the structure of
the continuous electronic component of the Raman scattering signal. The
temperatures inferred from the Raman signal are argued to be only of
qualitative value.Comment: 20 pages, 12 figure
Non-Gaussian dephasing in flux qubits due to 1/f-noise
Recent experiments by F. Yoshihara et al. [Phys. Rev. Lett. 97, 167001
(2006)] and by K. Kakuyanagi et al. (cond-mat/0609564) provided information on
decoherence of the echo signal in Josephson-junction flux qubits at various
bias conditions. These results were interpreted assuming a Gaussian model for
the decoherence due to 1/f noise. Here we revisit this problem on the basis of
the exactly solvable spin-fluctuator model reproducing detailed properties of
the 1/f noise interacting with a qubit. We consider the time dependence of the
echo signal and conclude that the results based on the Gaussian assumption need
essential reconsideration.Comment: Improved fitting parameters, new figur
A note on the perturbative properties of BPS operators
We discuss the perturbative behavior of the 1/2 BPS operators in N=2 SCFT on
the example of two very similar quadrilinear composite operators made out of
hypermultiplets. An explicit one-loop computation shows that one of them is
protected while the other acquires an anomalous dimension. Although both
operators are superconformal primaries in the free case, the quantum
corrections make the latter become a 1/2 BPS descendant of the Konishi
multiplet, while the former remains primary. The comparative study of these two
operators at higher orders may be helpful in understanding the quantum
properties of the Konishi multiplet
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