1,876 research outputs found
The New Cosmos
We review the broad status of cosmology and discuss a model of fluctuational
cosmology in which the universe is created in a phase transition like
phenomenon mimicking inflation, and which further consistently explains latest
observations like the ever expanding and accelerating feature.Comment: 10 pages, TeX,Inaugural address of the Physics Association of the
National Institute of Technology, Warangal, Andhra Pradesh, Indi
Correlation Functions in Holographic Minimal Models
We compute exact three and four point functions in the W_N minimal models
that were recently conjectured to be dual to a higher spin theory in AdS_3. The
boundary theory has a large number of light operators that are not only
invisible in the bulk but grow exponentially with N even at small conformal
dimensions. Nevertheless, we provide evidence that this theory can be
understood in a 1/N expansion since our correlators look like free-field
correlators corrected by a power series in 1/N . However, on examining these
corrections we find that the four point function of the two bulk scalar fields
is corrected at leading order in 1/N through the contribution of one of the
additional light operators in an OPE channel. This suggests that, to correctly
reproduce even tree-level correlators on the boundary, the bulk theory needs to
be modified by the inclusion of additional fields. As a technical by-product of
our analysis, we describe two separate methods -- including a Coulomb gas type
free-field formalism -- that may be used to compute correlation functions in
this theory.Comment: 21+23 page
Iterative graph cuts for image segmentation with a nonlinear statistical shape prior
Shape-based regularization has proven to be a useful method for delineating
objects within noisy images where one has prior knowledge of the shape of the
targeted object. When a collection of possible shapes is available, the
specification of a shape prior using kernel density estimation is a natural
technique. Unfortunately, energy functionals arising from kernel density
estimation are of a form that makes them impossible to directly minimize using
efficient optimization algorithms such as graph cuts. Our main contribution is
to show how one may recast the energy functional into a form that is
minimizable iteratively and efficiently using graph cuts.Comment: Revision submitted to JMIV (02/24/13
On Black Attractors in 8D and Heterotic/Type IIA Duality
Motivated by the study of black attractors in 8D supergravity with 16
supersymmetries, we use the field theory approach and 8D supersymmetry with non
trivial central charges to shed light on the exact duality between heterotic
string on T^2 and type IIA on real connected and compact surfaces {\Sigma}2. We
investigate the two constraints that should be obeyed by {\Sigma}2 and give
their solutions in terms of intersecting 2-cycles as well their classification
using Dynkin diagrams of affine Kac-Moody algebras. It is shown as well that
the moduli space of these dual theories is given by
SO(1,1)x((SO(2,r+2))/(SO(2)xSO(r+2))) where r stands for the rank of the gauge
symmetry G_{r} of the 10D heterotic string on T^2. The remarkable cases
r=-2,-1,0 as well as other features are also investigated.Comment: LaTex, 18 pages, 2 figures, To appear in JHE
Testing Models of Intrinsic Brightness Variations in Type Ia Supernovae, and their Impact on Measuring Cosmological Parameters
For spectroscopically confirmed Type Ia supernovae we evaluate models of
intrinsic brightness variations with detailed data/Monte Carlo comparisons of
the dispersion in the following quantities: Hubble-diagram scatter, color
difference (B-V-c) between the true B-V color and the fitted color (c) from the
SALT-II light curve model, and photometric redshift residual. The data sample
includes 251 ugriz light curves from the 3-season Sloan Digital Sky Survey-II,
and 191 griz light curves from the Supernova Legacy Survey 3-year data release.
We find that the simplest model of a wavelength-independent (coherent) scatter
is not adequate, and that to describe the data the intrinsic scatter model must
have wavelength-dependent variations. We use Monte Carlo simulations to examine
the standard approach of adding a coherent scatter term in quadrature to the
distance-modulus uncertainty in order to bring the reduced chi2 to unity when
fitting a Hubble diagram. If the light curve fits include model uncertainties
with the correct wavelength dependence of the scatter, we find that the bias on
the dark energy equation of state parameter is negligible. However,
incorrect model uncertainties can lead to a significant bias on the distance
moduli, with up to ~0.05 mag redshift-dependent variation. For the recent SNLS3
cosmology results we estimate that this effect introduces an additional
systematic uncertainty on of ~0.02, well below the total uncertainty.
However, this uncertainty depends on the samples used, and thus this small
-uncertainty is not guaranteed in future cosmology results.Comment: accepted by Ap
Silver mean conjectures for 15-d volumes and 14-d hyperareas of the separable two-qubit systems
Extensive numerical integration results lead us to conjecture that the silver
mean, that is, s = \sqrt{2}-1 = .414214 plays a fundamental role in certain
geometries (those given by monotone metrics) imposable on the 15-dimensional
convex set of two-qubit systems. For example, we hypothesize that the volume of
separable two-qubit states, as measured in terms of (four times) the minimal
monotone or Bures metric is s/3, and 10s in terms of (four times) the Kubo-Mori
monotone metric. Also, we conjecture, in terms of (four times) the Bures
metric, that that part of the 14-dimensional boundary of separable states
consisting generically of rank-four 4 x 4 density matrices has volume
(``hyperarea'') 55s/39 and that part composed of rank-three density matrices,
43s/39, so the total boundary hyperarea would be 98s/39. While the Bures
probability of separability (0.07334) dominates that (0.050339) based on the
Wigner-Yanase metric (and all other monotone metrics) for rank-four states, the
Wigner-Yanase (0.18228) strongly dominates the Bures (0.03982) for the
rank-three states.Comment: 30 pages, 6 tables, 17 figures; nine new figures and one new table in
new section VII.B pertaining to 14-dimensional hyperareas associated with
various monotone metric
Patterns of hepatocellular carcinoma incidence in Egypt from a population-based cancer registry
Hepatocellular carcinoma (HCC) is increasing worldwide, and is frequently attributed to rising rates of hepatitis C virus infection and interactions between viral and environmental risk factors. Because of Egypt's unique risk factor profile, we analyzed data from the Gharbiah Population-Based Cancer Registry for the period 1999–2003 to characterize demographic and geographic patterns of cases in this province. Methods:  We calculated age- and sex-specific and age- and sex-standardized HCC incidence rates for the eight districts in Gharbiah. We also compared rates from Gharbiah with the USA (US Surveillance Epidemiology and End Results [SEER] database). Results:  The analysis revealed a higher incidence in males than in females, significant geographic variations among districts, and a higher incidence in Gharbiah than that reported by SEER. Conclusion:  The findings of this study document the heterogeneous distribution of HCC at regional and international levels. This population-based registry offers the opportunity for careful representative studies of various etiologies, particularly infectious and/or environmental factors that may contribute to risk.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75374/1/j.1872-034X.2007.00299.x.pd
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