662 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
Harmonicity in N=4 supersymmetry and its quantum anomaly
The holomorphicity property of N=1 superpotentials or of N=2 F-terms
involving vector multiplets is generalized to the case of N=4 1/2-BPS effective
operators defined in harmonic superspace. The resulting harmonicity equations
are shown to control the moduli dependence of the couplings of higher
dimensional operators involving powers of the N=4 Weyl superfield, computed by
N=4 topological amplitudes. These equations can also be derived on the string
side, exhibiting an anomaly from world-sheet boundary contributions that leads
to recursion relations for the non-analytic part of the couplings.Comment: 36 page
Worldline Superfield Actions for N=2 Superparticles
We propose doubly supersymmetric actions in terms of n=2(D-2) worldline
superfields for N=2 superparticles in D=3,4 and Type IIA D=6 superspaces. These
actions are obtained by dimensional reduction of superfield actions for N=1
superparticles in D=4,6 and 10, respectively. We show that in all these models
geometrodynamical constraints on target superspace coordinates do not put the
theory on the mass shell, so the actions constructed consistently describe the
dynamics of the corresponding N=2 superparticles. We also find that in contrast
to the IIA D=6 superparticle a chiral IIB D=6 superparticle, which is not
obtainable by dimensional reduction from N=1, D=10, is described by superfield
constraints which produce dynamical equations. This implies that for the IIB
D=6 superparticle the doubly supersymmetric action does not exist in the
conventional form.Comment: Latex, 20 pp. Minor corrections, acknowledgements adde
A new Simplified Method of Selective Exposure of Hepatic Pedicles for Controlled Hepatectomies
Our experience of 90 hepatectomies (HE) and examinations of 64 cadaver livers resulted in the elaboration
of a simplified technique for the exposure of hepatic pedicles (HP) and the rapid selective ligation
without significant normothermal ischemia of the retained parts of the liver. The method comprises 4
consecutive steps: 1) a superficial T-shaped incision of Glisson's capsule at the site of HP projection
on the liver's inferior surface, 2) introduction of the surgeon's forefinger into the liver parenchyma,
controlled by clamping the hepatoduodenal ligament, the fingertip finding a tubular structure well distinguished
by its smooth elastic surface from the friable parenchyma and bending the finger to hook
the pedicle, 3) drawing the hooked pedicle downwards through the slit in the capsule and temporarily
clamping it, while releasing the hepatoduodenal ligament so as to restore blood supply to the retained
parts of the liver, 4) checking for correct ligature position on the HP before its final ligation by matching
the actual ischemic area with the intended line of resection and moving the clamp proximally or distally
along the exposed pedicle for the release or clamping of lateral branches as necessary. Whereupon
resection can be performed by any of the known methods
Harmonic Superspaces in Low Dimensions
Harmonic superspaces for spacetimes of dimension are constructed.
Some applications are given.Comment: 16, kcl-th-94-15. Two further references have been added (12 and 13)
and a few typographical errors have been correcte
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
Weinberg propagator of a free massive particle with an arbitrary spin from the BFV-BRST path integral
The transition amplitude is obtained for a free massive particle of arbitrary
spin by calculating the path integral in the index-spinor formulation within
the BFV-BRST approach. None renormalizations of the path integral measure were
applied. The calculation has given the Weinberg propagator written in the
index-free form with the use of index spinor. The choice of boundary conditions
on the index spinor determines holomorphic or antiholomorphic representation
for the canonical description of particle/antiparticle spin.Comment: 31 pages, Latex, version published in Class. Quantum Gra
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
New Model of Higher-Spin Particle
We elaborate on a new model of the higher-spin (HS) particle which makes
manifest the classical equivalence of the HS particle of the unfolded
formulation and the HS particle model with a bosonic counterpart of
supersymmetry. Both these models emerge as two different gauges of the new
master system. Physical states of the master model are massless HS multiplets
described by complex HS fields which carry an extra U(1) charge q. The latter
fully characterizes the given multiplet by fixing the minimal helicity as q/2.
We construct the twistorial formulation of the master model and discuss
symmetries of the new HS multiplets within its framework.Comment: 13 pages, talk given by E. Ivanov at the XII International Conference
on Symmetry Methods in Physics (SYMPHYS-XII), Yerevan, Armenia, July 03 - 08,
2006; to be published in the Proceeding
Nonlinearly driven Landau-Zener transition with telegraph noise
We study Landau-Zener like dynamics of a qubit influenced by transverse
random telegraph noise. The telegraph noise is characterized by its coupling
strength, and switching rate, . The qubit energy levels are driven
nonlinearly in time, \propto \sign(t)|t|^\nu, and we derive the transition
probability in the limit of sufficiently fast noise, for arbitrary exponent
. The longitudinal coherence after transition depends strongly on ,
and there exists a critical with qualitative difference between and . When the end state is always fully
incoherent with equal population of both quantum levels, even for arbitrarily
weak noise. For the system keeps some coherence depending on the
strength of the noise, and in the limit of weak noise no transition takes
place. For fast noise , while for slow noise and it
depends on . We also discuss transverse coherence, which is relevant
when the qubit has a nonzero minimum energy gap. The qualitative dependency on
is the same for transverse as for longitudinal coherence. The state after
transition does in general depend on . For fixed , increasing
decreases the final state coherence when and increase the
final state coherence when . Only the conventional linear driving is
independent of .Comment: 7 pages, 5 figure
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