541 research outputs found
Properties of and Mesons at Finite Temperature and Density as Inferred from Experiment
The mass shift, width broadening, and spectral density for the and
mesons in a heat bath of nucleons and pions are calculated using a
general formula which relates the self-energy to the real and imaginary parts
of the forward scattering amplitude. We use experimental data to saturate the
scattering amplitude at low energies with resonances and include a background
Pomeron term, while at high energies a Regge parameterization is used. The real
part obtained directly is compared with the result of a dispersion integral
over the imaginary part. The peaks of the spectral densities are little shifted
from their vacuum positions, but the widths are considerably increased due to
collisional broadening. Where possible we compare with the UrQMD model and find
quite good agreement. At normal nuclear matter density and a temperature of 150
MeV the spectral density of the meson has a width of 345 MeV, while that
for the is in the range 90--150 MeV.Comment: 21 pages revtex + 9 postscript figure
Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope
The CAT Imaging Telescope has observed the BL Lac object Markarian 501
between March and August 1997. We report here on the variability over this time
including several large flares. We present also preliminary spectra for all
these data, for the low emission state, and for the largest flare.Comment: 4 pages, 4 figures, Late
Observation of the Crab Nebula Gamma-Ray Emission Above 220 Gev by the Cat Cherenkov Imaging Telescope
The CAT imaging telescope, recently built on the site of the former solar
plant Themis (French Pyrenees), observed gamma-rays from the Crab nebula from
October 1996 to March 1997. This steady source, often considered as the
standard candle of very-high-energy gamma-ray astronomy, is used as a test-beam
to probe the performances of the new telescope, particularly its energy
threshold (220 GeV at 20 degrees zenith angle) and the stability of its
response. Due to the fine-grain camera, an accurate analysis of the
longitudinal profiles of shower images is performed, yielding the source
position in two dimensions for each individual shower.Comment: 5 pages, 3 figures, Tex, contribution to 25th ICRC Durba
Detection of Vhe Gamma-Rays from MRK 501 with the Cat Imaging Telescope
The CAT imaging telescope on the site on the former solar plant Themis has
been observing gamma-rays from Mrk501 above 220 GeV in March and April 1997.
This source is shown to be highly variable and the light curve is presented.
The detected gamma-ray rate for the most intense flare is in excess of 10 per
minute.Comment: 5 pages, 4 figures, Tex, contribution to 25th ICRC Durba
Delta rho pi interaction leading to N* and Delta* resonances
We have performed a calculation for the three body system
by using the fixed center approximation to Faddeev equations, taking the
interaction between and , and, and and
from the chiral unitary approach. We find several peaks in the modulus
squared of the three-body scattering amplitude, indicating the existence of
resonances, which can be associated to known and and baryon states.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201
Model dependence of single-energy fits to pion photoproduction data
Model dependence of multipole analysis has been explored through
energy-dependent and single-energy fits to pion photoproduction data. The MAID
energy-dependent solution has been used as input for an event generator
producing realistic pseudo data. These were fitted using the SAID
parametrization approach to determine single-energy and energy-dependent
solutions over a range of lab photon energies from 200 to 1200 MeV. The
resulting solutions were found to be consistent with the input amplitudes from
MAID. Fits with a -squared per datum of unity or less were generally
achieved. We discuss energy regions where consistent results are expected, and
explore the sensitivity of fits to the number of included single- and
double-polarization observables. The influence of Watson's theorem is examined
in detail.Comment: 12 pages, 8 figure
Genetic risk for schizophrenia and psychosis in Alzheimer disease
Psychotic symptoms, defined as the occurrence of delusions or hallucinations, are frequent in Alzheimer disease (AD), affecting ~40 to 60% of individuals with AD (AD with psychosis (AD+P)). In comparison with AD subjects without psychosis, AD+P subjects have more rapid cognitive decline and poor outcomes. Prior studies have estimated the heritability of psychosis in AD at 61%, but the underlying genetic sources of this risk are not known. We evaluated a Discovery Cohort of 2876 AD subjects with (N=1761) or without psychosis (N=1115). All subjects were genotyped using a custom genotyping array designed to evaluate single-nucleotide polymorphisms (SNPs) with evidence of genetic association with AD+P and include SNPs affecting or putatively affecting risk for schizophrenia and AD. Results were replicated in an independent cohort of 2194 AD subjects with (N=734) or without psychosis (N=1460). We found that AD+P is associated with polygenic risk for a set of novel loci and inversely associated with polygenic risk for schizophrenia. Among the biologic pathways identified by the associations of schizophrenia SNPs with AD+P are endosomal trafficking, autophagy and calcium channel signaling. To the best of our knowledge, these findings provide the first clear demonstration that AD+P is associated with common genetic variation. In addition, they provide an unbiased link between polygenic risk for schizophrenia and a lower risk of psychosis in AD. This provides an opportunity to leverage progress made in identifying the biologic effects of schizophrenia alleles to identify novel mechanisms protecting against more rapid cognitive decline and psychosis risk in AD
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