3,566 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
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
Brane Dynamics From Non-Linear Realizations
The action for a non-BPS p=2 brane embedded in a flat N=1, D=4 target
superspace is obtained through the method of nonlinear realizations of the
associated super-Poincare symmetries. The brane excitation modes correspond to
the Nambu-Goldstone degrees of freedom resulting from the broken space
translational symmetry and the target space supersymmetries. The action for
this p=2 brane is found to be an invariant synthesis of the Akulov-Volkov and
Nambu-Goto actions. The dual D2-brane Born-Infeld action is derived. The
invariant coupling of matter fields localized on the brane to the
Nambu-Goldstone modes is also obtained.Comment: 37 pages, no figures, revised version to appear in Phys. Rev.
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
Conformal Sigma Models with Anomalous Dimensions and Ricci Solitons
We present new non-Ricci-flat Kahler metrics with U(N) and O(N) isometries as
target manifolds of superconformally invariant sigma models with an anomalous
dimension. They are so-called Ricci solitons, special solutions to a Ricci-flow
equation. These metrics explicitly contain the anomalous dimension and reduce
to Ricci-flat Kahler metrics on the canonical line bundles over certain coset
spaces in the limit of vanishing anomalous dimension.Comment: 9 pages, no figure
Cool White Dwarfs Found in the UKIRT Infrared Deep Sky Survey
We present the results of a search for cool white dwarfs in the United
Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area
Survey (LAS). The UKIDSS LAS photometry was paired with the Sloan Digital Sky
Survey (SDSS) to identify cool hydrogen-rich white dwarf candidates by their
neutral optical colors and blue near-infrared colors, as well as faint Reduced
Proper Motion magnitudes. Optical spectroscopy was obtained at Gemini
Observatory, and showed the majority of the candidates to be newly identified
cool degenerates, with a small number of G- to K-type (sub)dwarf contaminants.
Our initial search of 280 deg2 of sky resulted in seven new white dwarfs with
effective temperature T_eff ~ 6000 K. The current followup of 1400 deg2 of sky
has produced thirteen new white dwarfs. Model fits to the photometry show that
seven of the newly identified white dwarfs have 4120 K <= T_eff <= 4480 K, and
cooling ages between 7.3 Gyr and 8.7 Gyr; they have 40 km/s <= v_tan <= 85 km/s
and are likely to be thick disk 10-11 Gyr-old objects. The other half of the
sample has 4610 K <= T_eff <= 5260 K, cooling ages between 4.3 Gyr and 6.9 Gyr,
and 60 km/s <= v_tan <= 100 km/s. These are either thin disk remnants with
unusually high velocities, or lower-mass remnants of thick disk or halo late-F
or G stars.Comment: To appear in ApJ, accepted April 18 2011. 34 pages include 11 Figures
and 5 Table
Oscillating p-Branes
Coset methods are used to construct the action describing the dynamics
associated with the spontaneous breaking of the Poincare symmetries of D
dimensional space-time due to the embedding of a p-brane with codimension
N=D-p-1. The resulting world volume action is an ISO(1,p+N) invariant
generalization of the Nambu-Goto action in d=p+1 dimensional space-time.
Analogous results are obtained for an AdS p-brane with codimension N embedded
in D dimensional AdS space, yielding an SO(2,p+N) invariant version of the
Nambu-Goto action in d=p+1 dimensional space-time. Attention is focused on a
supersymmetric extension of the D=6 Minkowski space case with an embedded p=3
brane; a particular realization of which is provided by a non-BPS vortex. Here
both the Nambu-Goto-Akulov-Volkov action and its dual tensor form are
presented.Comment: 25 pages, no figure
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