237 research outputs found
Towards the Gravity Dual of Quarkonium in the Strongly Coupled QCD Plasma
We build a "bottom-up" holographic model of charmonium by matching the
essential spectral data. We argue that this data must include not only the
masses but also the decay constants of the J/psi and psi' mesons. Relative to
the "soft-wall" models for light mesons, such a matching requires two new
features in the holographic potential: an overall upward shift as well as a
narrow "dip" near the holographic boundary. We calculate the spectral function
as well as the position of the complex singularities (quasinormal frequencies)
of the retarded correlator of the charm current at finite temperatures. We
further extend this analysis by showing that the residues associated with these
singularities are given by the boundary derivative of the appropriately
normalized quasinormal mode. We find that the "melting" of the J/psi spectral
peak occurs at a temperature of about 540 MeV, or 2.8 T_c, in good agreement
with lattice results.Comment: 13 pages, 9 figure
Roper Resonance and S_{11}(1535) from Lattice QCD
Using the constrained curve fitting method and overlap fermions with the
lowest pion mass at , we observe that the masses of the first
positive and negative parity excited states of the nucleon tend to cross over
as the quark masses are taken to the chiral limit. Both results at the physical
pion mass agree with the experimental values of the Roper resonance
() and (). This is seen for the first
time in a lattice QCD calculation. These results are obtained on a quenched
Iwasaki lattice with . We also extract the
ghost states (a quenched artifact) which are shown to decouple from
the nucleon interpolation field above . From the
quark mass dependence of these states in the chiral region, we conclude that
spontaneously broken chiral symmetry dictates the dynamics of light quarks in
the nucleon.Comment: 10 pages, 5 figures, revised version to appear in PL
Bulk spectral function sum rule in QCD-like theories with a holographic dual
We derive the sum rule for the spectral function of the stress-energy tensor
in the bulk (uniform dilatation) channel in a general class of strongly coupled
field theories. This class includes theories holographically dual to a theory
of gravity coupled to a single scalar field, representing the operator of the
scale anomaly. In the limit when the operator becomes marginal, the sum rule
coincides with that in QCD. Using the holographic model, we verify explicitly
the cancellation between large and small frequency contributions to the
spectral integral required to satisfy the sum rule in such QCD-like theories.Comment: 16 pages, 2 figure
Relativistic Quark Spin Coupling Effects in the Correlations Between Nucleon Electroweak Properties
We investigate the effect of different relativistic spin couplings of
constituent quarks on nucleon electroweak properties. Within each quark spin
coupling scheme the correlations between static electroweak observables are
found to be independent of the particular shape of the momentum part of the
nucleon light-front wave function. The neutron charge form factor is very
sensitive to different choices of spin coupling schemes once the magnetic
moment is fitted to the experimental value. However, it is found rather
insensitive to the details of the momentum part of the three-quark wave
function model.Comment: 23 pages, 13 figures, requires axodraw.sty 1 figure corrected, 1
refs. added, some changes in tex
Moments of Nucleon's Parton Distribution for the Sea and Valence Quarks from Lattice QCD
We extend the study of lowest moments, , of the parton
distribution function of the nucleon to include those of the sea quarks; this
entails a disconnected insertion calculation in lattice QCD. This is carried
out on a quenched lattice with Wilson fermion. The quark loops
are calculated with noise vectors and unbiased subtractions, and multiple
nucleon sources are employed to reduce the statistical errors. We obtain
5 signals for for the $u,d,$ and $s$ quarks, but is
consistent with zero within errors. We provide results for both the connected
and disconnected insertions. The perturbatively renormalized for the
strange quark at $\mu = 2$ GeV is $_{s+\bar{s}} = 0.027 \pm 0.006$ which is
consistent with the experimental result. The ratio of for vs.
in the disconnected insertion with quark loops is calculated to be . This is about twice as large as the phenomenologically fitted
from
experiments where and include both the connected and
disconnected insertion parts. We discuss the source and implication of this
difference.Comment: 50 Pages 58 Figure
Effectiveness of an Inpatient Movement Disorders Program for Patients with Atypical Parkinsonism
This paper investigated the effectiveness of an inpatient movement disorders program for patients with atypical parkinsonism, who typically respond poorly to pharmacologic intervention and are challenging to rehabilitate as outpatients. Ninety-one patients with atypical parkinsonism participated in an inpatient movement disorders program. Patients received physical, occupational, and speech therapy for 3 hours/day, 5 to 7 days/week, and pharmacologic adjustments based on daily observation and data. Differences between admission and discharge scores were analyzed for the functional independence measure (FIM), timed up and go test (TUG), two-minute walk test (TMW), Berg balance scale (BBS) and finger tapping test (FT), and all showed significant improvement on discharge (P > .001). Clinically significant improvements in total FIM score were evident in 74% of the patients. Results were similar for ten patients whose medications were not adjusted. Patients with atypical parkinsonism benefit from an inpatient interdisciplinary movement disorders program to improve functional status
Dressed spectral densities for heavy quark diffusion in holographic plasmas
We analyze the large frequency behavior of the spectral densities that govern
the generalized Langevin diffusion process for a heavy quark in the context of
the gauge/gravity duality. The bare Langevin correlators obtained from the
trailing string solution have a singular short-distance behavior. We argue that
the proper dressed spectral functions are obtained by subtracting the
zero-temperature correlators. The dressed spectral functions have a
sufficiently fast fall-off at large frequency so that the Langevin process is
well defined and the dispersion relations are satisfied. We identify the cases
in which the subtraction does not modify the associated low-frequency transport
coefficients. These include conformal theories and the non-conformal,
non-confining models. We provide several analytic and numerical examples in
conformal and non-conformal holographic backgrounds.Comment: 51 pages, 2 figure
The barrel DIRC of PANDA
Cooled antiproton beams of unprecedented intensities in the momentum range of 1.5-15 GeV/c will be used for the PANDA experiment at FAIR to perform high precision experiments in the charmed quark sector. The PANDA detector will investigate antiproton annihilations with beams in the momentum range of 1.5 GeV/c to 15 GeV/c on a fixed target. An almost 4π acceptance double spectrometer is divided in a forward spectrometer and a target spectrometer. The charged particle identification in the latter is performed by ring imaging Cherenkov counters employing the DIRC principle
Host Genetic Factors and Vaccine-Induced Immunity to Hepatitis B Virus Infection
BACKGROUND: Vaccination against hepatitis B virus infection (HBV) is safe and effective; however, vaccine-induced antibody level wanes over time. Peak vaccine-induced anti-HBs level is directly related to antibody decay, as well as risk of infection and persistent carriage despite vaccination. We investigated the role of host genetic factors in long-term immunity against HBV infection based on peak anti-HBs level and seroconversion to anti-HBc. METHODS: We analyzed 715 SNP across 133 candidate genes in 662 infant vaccinees from The Gambia, assessing peak vaccine-induced anti-HBs level and core antibody (anti-HBc) status, whilst adjusting for covariates. A replication study comprised 43 SNPs in a further 393 individuals. RESULTS: In our initial screen we found variation in IFNG, MAPK8, and IL10RA to affect peak anti-HBs level (GMTratio of 1.5 and P < or = 0.001) and lesser associations in other genes. Odds of core-conversion was associated with variation in CD163. A coding change in ITGAL (R719V) with likely functional relevance showed evidence of association with increased peak anti-HBs level in both screens (1st screen: s595_22 GMTratio 1.71, P = 0.013; 2nd screen: s595_22 GMTratio 2.15, P = 0.011). CONCLUSION: This is to our knowledge the largest study to date assessing genetic determinants of HBV vaccine-induced immunity. We report on associations with anti-HBs level, which is directly related to durability of antibody level and predictive of vaccine efficacy long-term. A coding change in ITGAL, which plays a central role in immune cell interaction, was shown to exert beneficial effects on induction of peak antibody level in response to HBV vaccination. Variation in this gene does not appear to have been studied in relation to immune responses to viral or vaccine challenges previously. Our findings suggest that genetic variation in loci other than the HLA region affect immunity induced by HBV vaccination
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