4,544 research outputs found
A Note on Supersymmetric WZW term in Four Dimensions
We reconsider the supersymmetric Wess-Zumino-Witten (SWZW) term in four
dimensions. It has been known that the manifestly supersymmetric form of the
SWZW term includes derivative terms on auxiliary fields, the highest components
of chiral superfields, and then we cannot eliminate them by their equations of
motion. We discuss a possibility for the elimination of such derivative terms
by adding total derivative terms. Although the most of derivative terms can be
eliminated as in this way, we find that all the derivative terms can be
canceled, if and only if an anomalous term in SWZW term vanishes. As a
byproduct, we find the first example of a higher derivative term free from such
a problem.Comment: LaTeX, 10 pages, no figures, typos corrected, references added,
accepted for publication in Modern Physics Letters
The Effect of Hydrostatic Weighting on the Vertical Temperature Structure of the Solar Corona
We investigate the effect of hydrostatic scale heights in
coronal loops on the determination of the vertical temperature structure
of the solar corona. Every method that determines an average temperature at a
particular line-of-sight from optically thin emission (e.g. in EUV or soft
X-ray wavelengths) of a mutli-temperature plasma, is subject to the emission
measure-weighted contributions from different temperatures. Because
most of the coronal structures (along open or closed field lines) are close to
hydrostatic equilibrium, the hydrostatic temperature scale height introduces a
height-dependent weighting function that causes a systematic bias in the
determination of the temperature structure as function of altitude .
The net effect is that the averaged temperature seems to increase with
altitude, , even if every coronal loop (of a multi-temperature
ensemble) is isothermal in itself. We simulate this effect with differential
emission measure distributions observed by {\sl SERTS} for an instrument with a
broadband temperature filter such as {\sl Yohkoh/SXT} and find that the
apparent temperature increase due to hydrostatic weighting is of order \Delta
T \approx T_0 \times h/r_{\sun}. We suggest that this effect largely explains
the systematic temperature increase in the upper corona reported in recent
studies (e.g. by Sturrock et al., Wheatland et al., or Priest et al.), rather
than being an intrinsic signature of a coronal heating mechanism.Comment: 7 pages, 3 figures. ApJ Letters, accepted 2000 April 6, in pres
Majorana meets Coxeter: Non-Abelian Majorana Fermions and Non-Abelian Statistics
We discuss statistics of vortices having zero-energy non-Abelian Majorana
fermions inside them. Considering the system of multiple non-Abelian vortices,
we derive a non-Abelian statistics that differs from the previously derived
non-Abelian statistics. The new non-Abelian statistics presented here is given
by a tensor product of two different groups, namely the non-Abelian statistics
obeyed by the Abelian Majorana fermions and the Coxeter group. The Coxeter
group is a symmetric group related to the symmetry of polytopes in a
high-dimensional space. As the simplest example, we consider the case in which
a vortex contains three Majorana fermions that are mixed with each other under
the SO(3) transformations. We concretely present the representation of the
Coxeter group in our case and its geometrical expressions in the
high-dimensional Hilbert space constructed from non-Abelian Majorana fermions.Comment: 6 pages, 4 figures, references added, published versio
SDSS White Dwarf mass distribution at low effective temperatures
The DA white dwarfs in the Sloan Digital Sky Survey, as analyzed in the
papers for Data Releases 1 and 4, show an increase in surface gravity towards
lower effective temperatures below 11500 K. We study the various possible
explanations of this effect, from a real increase of the masses to
uncertainties or deficiencies of the atmospheric models. No definite answer is
found but the tentative conclusion is that it is most likely the current
description of convection in the framework of the mixing-length approximation,
which leads to this effect.Comment: to appear in the proceedings of the 16th European Workshop on White
Dwarfs, Barcelona, 200
Unusual Tunneling Characteristics of Double-quantum-well Heterostructures
We report tunneling phenomena in double InGaAs quantum-well
structures that are at odds with the conventional parallel-momentum-conserving
picture of tunneling between two-dimensional systems. We found that the
tunneling current was mostly determined by the correlation between the emitter
and the state in one well, and not by that between those in both wells. Clear
magnetic-field-dependent features were first observed before the main
resonance, corresponding to tunneling channels into the Landau levels of the
well near the emitter. These facts provide evidence of the violation of
in-plane momentum conservation in two-dimensional systems.Comment: Submitted to ICPS-27 conference proceeding as a contributed pape
Statistical significance of fine structure in the frequency spectrum of Aharonov-Bohm conductance oscillations
We discuss a statistical analysis of Aharonov-Bohm conductance oscillations
measured in a two-dimensional ring, in the presence of Rashba spin-orbit
interaction. Measurements performed at different values of gate voltage are
used to calculate the ensemble-averaged modulus of the Fourier spectrum and, at
each frequency, the standard deviation associated to the average. This allows
us to prove the statistical significance of a splitting that we observe in the
h/e peak of the averaged spectrum. Our work illustrates in detail the role of
sample specific effects on the frequency spectrum of Aharonov-Bohm conductance
oscillations and it demonstrates how fine structures of a different physical
origin can be discriminated from sample specific features.Comment: accepted for publication in PR
Slow shocks and conduction fronts from Petschek reconnection of skewed magnetic fields: two-fluid effects
In models of fast magnetic reconnection, flux transfer occurs within a small
portion of a current sheet triggering stored magnetic energy to be thermalized
by shocks. When the initial current sheet separates magnetic fields which are
not perfectly anti-parallel, i.e. they are skewed, magnetic energy is first
converted to bulk kinetic energy and then thermalized in slow magnetosonic
shocks. We show that the latter resemble parallel shocks or hydrodynamic shocks
for all skew angles except those very near the anti-parallel limit. As for
parallel shocks, the structures of reconnection-driven slow shocks are best
studied using two-fluid equations in which ions and electrons have independent
temperature. Time-dependent solutions of these equations can be used to predict
and understand the shocks from reconnection of skewed magnetic fields. The
results differ from those found using a single-fluid model such as
magnetohydrodynamics. In the two-fluid model electrons are heated indirectly
and thus carry a heat flux always well below the free-streaming limit. The
viscous stress of the ions is, however, typically near the fluid-treatable
limit. We find that for a wide range of skew angles and small plasma beta an
electron conduction front extends ahead of the slow shock but remains within
the outflow jet. In such cases conduction will play a more limited role in
driving chromospheric evaporation than has been predicted based on
single-fluid, anti-parallel models
Spin-Hall effect in two-dimensional mesoscopic hole systems
The spin Hall effect in two dimensional hole systems is studied by using the
four-terminal Landauer-B\"{u}ttiker formula with the help of Green functions.
The spin Hall effect exists even when there are {\em not} any correlations
between the spin-up and -down heavy holes (light holes) and when the
-point degeneracy of the heavy hole and light hole bands is lifted by
the confinement or recovered by the strain. When only a heavy hole charge
current without any spin polarization is injected through one lead, under right
choice of lead voltages, one can get a pure heavy (light) hole spin current,
combined with a possible impure light (heavy) hole spin current from another
two leads. The spin Hall coefficients of both heavy and light holes depend on
the Fermi energy, devise size and the disorder strength. It is also shown that
the spin Hall effect of two dimensional hole systems is much more robust than
that of electron systems with the Rashba spin-orbit coupling and the spin Hall
coefficients do not decrease with the system size but tend to some nonzero
values when the disorder strength is smaller than some critical value.Comment: 5 pages, 4 figure
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