7,090 research outputs found
Gravitational Lens Statistics and The Density Profile of Dark Halos
We investigate the influence of the inner profile of lens objects on
gravitational lens statistics taking into account of the effect of
magnification bias and both the evolution and the scatter of halo profiles. We
take the dark halos as the lens objects and consider the following three models
for the density profile of dark halos; SIS (singular isothermal sphere), the
NFW (Navarro Frenk White) profile, and the generalized NFW profile which has a
different slope at smaller radii. The mass function of dark halos is assumed to
be given by the Press-Schechter function. We find that magnification bias for
the NFW profile is order of magnitude larger than that for SIS. We estimate the
sensitivity of the lensing probability of distant sources to the inner profile
of lenses and to the cosmological parameters. It turns out that the lensing
probability is strongly dependent on the inner density profile as well as on
the cosmological constant. We compare the predictions with the largest
observational sample, the Cosmic Lens All-Sky Survey. The absence or presence
of large splitting events in larger surveys currently underway such as the 2dF
and SDSS could set constraints on the inner density profile of dark halos.Comment: 22 pages, minor changes and references added, accepted for
publication in Ap
Remote preparation of arbitrary ensembles and quantum bit commitment
The Hughston-Jozsa-Wootters theorem shows that any finite ensemble of quantum
states can be prepared "at a distance", and it has been used to demonstrate the
insecurity of all bit commitment protocols based on finite quantum systems
without superselection rules. In this paper, we prove a generalized HJW theorem
for arbitrary ensembles of states on a C*-algebra. We then use this result to
demonstrate the insecurity of bit commitment protocols based on infinite
quantum systems, and quantum systems with Abelian superselection rules.Comment: 21 pages, LaTeX. Version 2: Proofs expanded and made more
self-contained; added an example of a bit commitment protocol with continuous
ensemble
Finite-size Scaling of Correlation Ratio and Generalized Scheme for the Probability-Changing Cluster Algorithm
We study the finite-size scaling (FSS) property of the correlation ratio, the
ratio of the correlation functions with different distances. It is shown that
the correlation ratio is a good estimator to determine the critical point of
the second-order transition using the FSS analysis. The correlation ratio is
especially useful for the analysis of the Kosterlitz-Thouless (KT) transition.
We also present a generalized scheme of the probability-changing cluster
algorithm, which has been recently developed by the present authors, based on
the FSS property of the correlation ratio. We investigate the two-dimensional
quantum XY model of spin 1/2 with this generalized scheme, obtaining the
precise estimate of the KT transition temperature with less numerical effort.Comment: 4 pages, RevTeX4, to appear in Phys. Rev. B, Rapid Communication
Low Energy Effective Action for Horava-Witten Cosmology
As a supersymmetric extension of the Randall-Sundrum model, we consider a
5-dimensional Horava-Witten type theory, and derive its low energy effective
action. The model we consider is a two-brane system with a bulk scalar field
satisfying the BPS condition. We solve the bulk equations of motion using a
gradient expansion method, and substitute the solution into the original action
to get the 4-dimensional effective action. The resultant effective theory can
be casted into the form of Einstein gravity coupled with two scalar fields, one
arising from the radion, the degree of freedom of the inter-brane distance, and
the other from the bulk scalar field. We also clarify the relation between our
analysis and the moduli approximation.Comment: 11 page
Measured Quantum Fourier Transform of 1024 Qubits on Fiber Optics
Quantum Fourier transform (QFT) is a key function to realize quantum
computers. A QFT followed by measurement was demonstrated on a simple circuit
based on fiber-optics. The QFT was shown to be robust against imperfections in
the rotation gate. Error probability was estimated to be 0.01 per qubit, which
corresponded to error-free operation on 100 qubits. The error probability can
be further reduced by taking the majority of the accumulated results. The
reduction of error probability resulted in a successful QFT demonstration on
1024 qubits.Comment: 15 pages, 6 figures, submitted to EQIS 2003 Special issue, Int. J.
Quantum Informatio
Photometric Observations of Star Formation Activity in Early Type Spirals
We observationally study the current star formation activities of early type
spiral galaxies. We construct a complete sample of 15 early type spirals having
far-infrared (FIR) to optical B band luminosity ratios, L(FIR)/L(B), larger
than the average of the type, and make their CCD imaging of the R and H-alpha
bands. The equivalent widths of H-alpha emission increase with increasing
L(FIR)/L(B), indicating that L(FIR)/L(B) can be an indicator of star formation
for such early type spirals with star formation activities higher than the
average. For all of the observed early type spirals, the extended HII regions
exist at the central regions with some asymmetric features. H-alpha emission is
more concentrated to the galactic center than the R band light, and the degree
of the concentration increases with the star formation activity. We also
analyze the relation between the star formation activities and the existence of
companion galaxies in the sample galaxies and other bright early type spirals.
No correlation is found and this suggests that the interaction is not
responsible for all of the star formation activities of early type spirals.Comment: LaTex, 23 pages (2 tables included), plus 9 Postscript figures & 1
table. To be published in AJ (November issue
Enhancement of the Critical Current Density of YBa2Cu3Ox Superconductors under Hydrostatic Pressure
The dependence of the critical current density Jc on hydrostatic pressure to
0.6 GPa is determined for a single 25-degree [001]-tilt grain boundary in a
bicrystalline ring of nearly optimally doped melt-textured YBa2Cu3Ox. Jc is
found to increase rapidly under pressure at +20 %/GPa. A new diagnostic method
is introduced (pressure-induced Jc relaxation) which reveals a sizeable
concentration of vacant oxygen sites in the grain boundary region. Completely
filling such sites with oxygen anions should lead to significant enhancements
in Jc.Comment: revised manuscript, graphic errors in figures correcte
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