16,835 research outputs found
Higgs Decays and Brane Gravi-vectors
Higgs boson decays in flexible brane world models with stable, massive
gravi-vectors are considered. Such vectors couple bilinearly to the Standard
Model fields through either the Standard Model energy-momentum tensor, the weak
hypercharge field strength or the Higgs scalar. The role of the coupling
involving the extrinsic curvature is highlighted. It is found that within the
presently allowed parameter space, the decay rate of the Higgs into two
gravi-vectors (which would appear as an invisible Higgs decay) can be
comparable to the rate for any of the Standard Model decay modes.Comment: 5 pages, 11 figures, revte
Wind and Solar Energy Driven RO Brackish Water Desalination
The principal objective of this Research project was to develop a simple cost-effective desalination system for Pacific islands and other remote coastal communities where both freshwater and electricity are in short supply
Closed-form solutions of the Schroedinger equation for a class of smoothed Coulomb potentials
An infinite family of closed-form solutions is exhibited for the Schroedinger
equation for the potential . Evidence is
presented for an approximate dynamical symmetry for large values of the angular
momentum .Comment: 13 pages LaTeX, uses included Institute of Physics style files, 3
PostScript figures. In press at J. Phys. B: At. Mol. Opt. Phys. (1997
Dynamics of Weyl Scale Invariant non-BPS p=3 Branes
In this paper a Weyl scale invariant brane scenario is introduced, with
the brane embedded in a higher dimensional bulk space with
Super--Weyl symmetry. Its action, which describes its long wave oscillation
modes into the ambient superspace and breaks the target symmetry down to the
lower dimensional Weyl W(1,3) symmetry, is constructed by the approach of coset
method.Comment: 12 pages, modified versio
Clock Synchronized Transmission of 51.2 GBd Optical Packets for Optically Switched Data Center Interconnects
NGC300 X-1 and IC10 X-1: a new breed of black hole binary?
[ABRIDGED] IC10 X-1 has recently been confirmed as a black hole (BH) +
Wolf-Rayet (WR) X-ray binary, and NGC300 X-1 is thought to be. IC10 X-1 and
NGC300 X-1 have similar X-ray properties, with luminosities ~10^38 erg/s, and
orbital periods ~30 hr. We investigate similarities between these two, as well
as differences between them and the known Galactic BH binary systems. We have
examined XMM-Newton observations of NGC300 X-1 and IC10 X-1. We extracted
lightcurves and spectra; power density spectra (PDS) were constructed from the
lightcurves, and the X-ray emission spectra were modeled. Each source exhibits
PDS that are characteristic of disc-accreting X-ray binaries (XBs) in the high
state. In this state, Galactic XBs with known BH primaries have soft, thermal
emission; however the emission spectra of our targets are predominantly
non-thermal. Furthermore, the Observation 1 spectrum of NGC300 X-1 is
strikingly similar to that of IC10 X-1. The remarkable similarity between the
behaviour of NGC300 X-1 in Observation 1 and that of IC10 X-1 lends strong
evidence for NGC300 X-1 being a (BH+WR) binary. The unusual spectra of NGC300
X-1 and IC10 X-1 may be due to these systems existing in a persistently high
state, whereas all known BH LMXBs are transient. BH XBs in a persistent high
state could retain their corona, and hence exhibit a large non-thermal
component. LMC X-1 is a BH XB that has only been observed in the high state,
and its spectrum is remarkably similar to those of our targets. We therefore
classify NGC300 X-1, IC10 X-1 and perhaps LMC X-1 as a new breed of BH XB,
defined by their persistently high accretion rates and consequent stable disc
configuration and corona. This scenario may also explain the lack of
ultraluminous X-ray sources in the canonical soft state.Comment: Approved for publication in A&A. 8 pages, 5 figure
Nonlinear Realization of N=2 Superconformal Symmetry and Brane Effective Actions
Due to the incompatibility of the nonlinear realization of superconformal
symmetry and dilatation symmetry with the dilaton as the compensator field, in
the present paper it shows an alternative mechanism of spontaneous breaking the
N=2 superconformal symmetry to the N=0 case. By using the approach of nonlinear
transformations it is found that it leads to a space-filling brane theory with
Weyl scale W(1,3) symmetry. The dynamics of the resulting Weyl scale invariant
brane, along with that of other Nambu-Goldstone fields, is derived in terms of
the building blocks of the vierbein and the covariant derivative from the
Maurer-Cartan oneforms. A general coupling of the matter fields localized on
the brane world volume to these NG fields is also constructed.Comment: 22 pages, more references and comments are adde
Toward a Clean Sample of Ultra-Luminous X-ray Sources
CONTEXT. Observational follow-up programmes for the characterization of
ultra-luminous X-ray sources (ULXs) require the construction of clean samples
of such sources in which the contamination by foreground/background sources is
minimum.
AIMS. In this article we calculate the degree of foreground/background
contaminants among the ULX sample candidates in the Colbert & Ptak (2002)
catalogue and compare these computations with available spectroscopical
identifications.
METHODS. We use statistics based on known densities of X-ray sources and
AGN/QSOs selected in the optical. The analysis is done individually for each
parent galaxy. The existing identifications of the optical counterparts are
compiled from the literature.
RESULTS. More than a half of the ULXs, within twice the distance of the major
axis of the 25 mag/arcsec isophote from RC3 nearby galaxies and with X-ray
luminosities [2-10 keV] erg/s, are expected to be high
redshift background QSOs. A list of 25 objects (clean sample) confirmed to be
real ULXs or to have a low probability of being contaminant
foreground/background objects is provided.Comment: 9 pages, accepted in A&
Hardware and software status of QCDOC
QCDOC is a massively parallel supercomputer whose processing nodes are based
on an application-specific integrated circuit (ASIC). This ASIC was
custom-designed so that crucial lattice QCD kernels achieve an overall
sustained performance of 50% on machines with several 10,000 nodes. This strong
scalability, together with low power consumption and a price/performance ratio
of $1 per sustained MFlops, enable QCDOC to attack the most demanding lattice
QCD problems. The first ASICs became available in June of 2003, and the testing
performed so far has shown all systems functioning according to specification.
We review the hardware and software status of QCDOC and present performance
figures obtained in real hardware as well as in simulation.Comment: Lattice2003(machine), 6 pages, 5 figure
Theory of Phonon Shakeup Effects on Photoluminescence from the Wigner Crystal in a Strong Magnetic Field
We develop a method to compute shakeup effects on photoluminescence from a
strong magnetic field induced two-dimensional Wigner crystal. Only localized
holes are considered. Our method treats the lattice electrons and the tunneling
electron on an equal footing, and uses a quantum-mechanical calculation of the
collective modes that does not depend in any way on a harmonic approximation.
We find that shakeup produces a series of sidebands that may be identified with
maxima in the collective mode density of states, and definitively distinguishes
the crystal state from a liquid state in the absence of electron-hole
interaction. In the presence of electron-hole interaction, sidebands also
appear in the liquid state coming from short-range density fluctuations around
the hole. However, the sidebands in the liquid state and the crystal state have
different qualitative behaviors. We also find a shift in the main luminescence
peak, that is associated with lattice relaxation in the vicinity of a vacancy.
The relationship of the shakeup spectrum with previous mean-field calculations
is discussed.Comment: 14 pages, uuencoded postscript file for entire paper, also available
at (click phd14) http://rainbow.uchicago.edu/~ldz/paper/paper.htm
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