6,242 research outputs found
The super algebra and its associated generalized KdV hierarchies
We construct the super algebra as a certain reduction of the
second Gel'fand-Dikii bracket on the dual of the Lie superalgebra of
super pseudo-differential operators. The algebra is put in manifestly
supersymmetric form in terms of three superfields , with
being the energy momentum tensor and and being
conformal spin and superfields respectively. A search for integrable
hierarchies of the generalized KdV variety with this algebra as Hamiltonian
structure gives three solutions, exactly the same number as for the
(super KdV) and (super Boussinesq) cases.Comment: 16 pages, LaTeX, UTAS-PHYS-92-3
Iron-Line Emission as a Probe of Bardeen-Petterson Accretion Disks
In this work we show that Bardeen-Petterson accretion disks can exhibit
unique, detectable features in relativistically broadened emission line
profiles. Some of the unique characteristics include inverted line profiles
with sharper red horns and softer blue horns and even profiles with more than 2
horns from a single rest-frame line. We demonstrate these points by
constructing a series of synthetic line profiles using simple two-component
disk models. We find that the resultant profiles are very sensitive to the two
key parameters one would like to constrain, namely the Bardeen-Petterson
transition radius r_{BP} and the relative tilt \beta between the two disk
components over a range of likely values [10 < r_{BP}/(GM/c^2) < 40 ; 15deg <
\beta < 45deg]. We use our findings to show that some of the ``extra'' line
features observed in the spectrum of the Seyfert-I galaxy MCG--6-30-15 may be
attributable to a Bardeen-Petterson disk structure. Similarly, we apply our
findings to two likely Bardeen-Petterson candidate Galactic black holes - GRO
J1655-40 and XTE J1550-564. We provide synthetic line profiles of these systems
using observationally constrained sets of parameters. Although we do not
formally fit the data for any of these systems, we confirm that our synthetic
spectra are consistent with current observations.Comment: 13 pages, 11 figures, submitted to Ap
Partial Dynamical SU(3) Symmetry and the Nature of the Lowest K=0 Collective Excitation in Deformed Nuclei
We discuss the implications of partial dynamical SU(3) symmetry (PDS) for the
structure of the lowest K=0^{+} (K=0_2) collective excitation in deformed
nuclei. We consider an interacting boson model Hamiltonian whose ground and
gamma bands have good SU(3) symmetry while the K=0_2 band is mixed. It is shown
that the double-phonon components in the K=0_2 wave function arise from SU(3)
admixtures which, in turn, can be determined from absolute E2 rates connecting
the K=0_2 and ground bands. An explicit expression is derived for these
admixtures in terms of the ratio of K=0_2 and gamma bandhead energies. The
SU(3) PDS predictions are compared with existing data and with broken-SU(3)
calculations for ^{168}Er.Comment: 12 pages, 2 figure
Forbidden Transitions in a Magneto-Optical Trap
We report the first observation of a non-dipole transition in an ultra-cold
atomic vapor. We excite the 3P-4P electric quadrupole (E2) transition in
Na confined in a Magneto-Optical Trap(MOT), and demonstrate its
application to high-resolution spectroscopy by making the first measurement of
the hyperfine structure of the 4P level and extracting the magnetic
dipole constant A 30.6 0.1 MHz. We use cw OODR (Optical-Optical
Double Resonance) accompanied by photoinization to probe the transition
Supergravity Instabilities of Non-Supersymmetric Quantum Critical Points
Motivated by the recent use of certain consistent truncations of M-theory to
study condensed matter physics using holographic techniques, we study the
SU(3)-invariant sector of four-dimensional, N=8 gauged supergravity and compute
the complete scalar spectrum at each of the five non-trivial critical points.
We demonstrate that the smaller SU(4)^- sector is equivalent to a consistent
truncation studied recently by various authors and find that the critical point
in this sector, which has been proposed as the ground state of a holographic
superconductor, is unstable due to a family of scalars that violate the
Breitenlohner-Freedman bound. We also derive the origin of this instability in
eleven dimensions and comment on the generalization to other embeddings of this
critical point which involve arbitrary Sasaki-Einstein seven manifolds. In the
spirit of a resurging interest in consistent truncations, we present a formal
treatment of the SU(3)-invariant sector as a U(1)xU(1) gauged N=2 supergravity
theory coupled to one hypermultiplet.Comment: 46 page
Constraints in Quantum Geometrodynamics
We compare different treatments of the constraints in canonical quantum
gravity. The standard approach on the superspace of 3--geometries treats the
constraints as the sole carriers of the dynamic content of the theory, thus
rendering the traditional dynamical equations obsolete. Quantization of the
constraints in both the Dirac and ADM square root Hamiltonian approaches leads
to the well known problems of time evolution. These problems of time are of
both an interpretational and technical nature. In contrast, the geometrodynamic
quantization procedure on the superspace of the true dynamical variables
separates the issues of quantization from the enforcement of the constraints.
The resulting theory takes into account states that are off-shell with respect
to the constraints, and thus avoids the problems of time. We develop, for the
first time, the geometrodynamic quantization formalism in a general setting and
show that it retains all essential features previously illustrated in the
context of homogeneous cosmologies.Comment: 36 pages, no figures, submitted to IJMPA, Rewording, Fixed Typo
Molecular Hydrogen Emission Lines in Far Ultraviolet Spectroscopic Explorer Observations of Mira B
We present new Far Ultraviolet Spectroscopic Explorer (FUSE) observations of
Mira A's wind-accreting companion star, Mira B. We find that the strongest
lines in the FUSE spectrum are H2 lines fluoresced by H I Lyman-alpha. A
previously analyzed Hubble Space Telescope (HST) spectrum also shows numerous
Lyman-alpha fluoresced H2 lines. The HST lines are all Lyman band lines, while
the FUSE H2 lines are mostly Werner band lines, many of them never before
identified in an astrophysical spectrum. We combine the FUSE and HST data to
refine estimates of the physical properties of the emitting H2 gas. We find
that the emission can be reproduced by an H2 layer with a temperature and
column density of T=3900 K and log N(H2)=17.1, respectively. Another similarity
between the HST and FUSE data, besides the prevalence of H2 emission, is the
surprising weakness of the continuum and high temperature emission lines,
suggesting that accretion onto Mira B has weakened dramatically. The UV fluxes
observed by HST on 1999 August 2 were previously reported to be over an order
of magnitude lower than those observed by HST and the International Ultraviolet
Explorer (IUE) from 1979--1995. Analysis of the FUSE data reveals that Mira B
was still in a similarly low state on 2001 November 22.Comment: 23 pages, 6 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty;
accepted by Ap
Simultaneous Acquisition of the Polarized and Depolarized Raman Signal with a Single Detector
Peer reviewedPublisher PD
Electro-Mechanical Fredericks Effects in Nematic Gels
The solid nematic equivalent of the Fredericks transition is found to depend
on a critical field rather than a critical voltage as in the classical case.
This arises because director anchoring is principally to the solid rubbery
matrix of the nematic gel rather than to the sample surfaces. Moreover, above
the threshold field, we find a competition between quartic (soft) and
conventional harmonic elasticity which dictates the director response. By
including a small degree of initial director misorientation, the calculated
field variation of optical anisotropy agrees well with the conoscopy
measurements of Chang et al (Phys.Rev.E56, 595, 1997) of the electro-optical
response of nematic gels.Comment: Latex (revtex style), 5 EPS figures, submitted to PRE, corrections to
discussion of fig.3, cosmetic change
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