128 research outputs found
Dynamic versus Static Structure Functions and Novel Diffractive Effects in QCD
Initial- and final-state rescattering, neglected in the parton model, have a
profound effect in QCD hard-scattering reactions, predicting single-spin
asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic
reactions, the breakdown of the Lam Tung relation in Drell-Yan reactions, and
nuclear shadowing and non-universal antishadowing--leading-twist physics not
incorporated in the light-front wavefunctions of the target computed in
isolation. I also discuss the use of diffraction to materialize the Fock states
of a hadronic projectile and test QCD color transparency, and anomalous heavy
quark effects. The presence of direct higher-twist processes where a proton is
produced in the hard subprocess can explain the large proton-to-pion ratio seen
in high centrality heavy ion collisions. I emphasize the importance of
distinguishing between static observables such as the probability distributions
computed from the square of the light-front wavefunctions versus dynamical
observables which include the effects of rescattering.Comment: 8 pages, 1 figure. Presented at Diffraction 2008: International
Workshop On Diffraction In High Energy Physics 9-14 Sep 2008, La
Londe-les-Maures, Franc
AdS/QCD and its Holographic Light-Front Partonic Representation
Starting from the Hamiltonian equation of motion in QCD we find a single
variable light-front equation for QCD which determines the eigenspectrum and
the light-front wavefunctions of hadrons for general spin and orbital angular
momentum. This light-front wave equation is equivalent to the equations of
motion which describe the propagation of spin- modes on anti-de Sitter (AdS)
space.Comment: 5 pages, 1 figure. Presented by GdT at Diffraction 2008,
International Workshop on Diffraction in High Energy Physic
Nucleon Helicity in Pion Photoproduction
Pion-photoproduction data is examined to check for the nucleon-helicity
conservation predicted by asymptotic QCD. The differential cross section shows
agreement with constituent-counting rules, and polarization data is not in
disagreement with conservation of nucleon helicity. However large uncertainties
in the polarization measurements do not allow a conclusive statement. The
helicity amplitudes from a partial-wave analysis are also examined for helicity
conservation. While the amplitudes become small as increases, the
dependence of the helicity-conserving amplitudes is similar to the dependence
of the non-conserving amplitudes.Comment: plain tex, 6 pages, 8 figure
Activation of Ca2+-activated Cl- current by depolarizing steps in rabbit urethral interstitial cells.
Interstitial cells were isolated from strips of rabbit urethra for study using the amphotericin B perforated-patch technique. Depolarizing steps to -30 mV or greater activated a Ca2+ current (ICa), followed by a Ca2+-activated Cl- current, and, on stepping back to -80 mV, large Cl- tail currents were observed. Both currents were abolished when the cells were superfused with Ca2+-free bath solution, suggesting that Ca2+ influx was necessary for activation of the Cl- current. The Cl- current was also abolished when Ba2+ was substituted for Ca2+ in the bath or the cell was dialyzed with EGTA (2 mM). The Cl- current was also reduced by cyclopiazonic acid, ryanodine, 2-aminoethoxydiphenyl borate (2-APB), and xestospongin C, suggesting that Ca2+-induced Ca2+ release (CICR) involving both ryanodine and inositol 1,4,5-trisphosphate receptors contributes to its activation
Hard diffractive electroproduction, transverse momentum distribution and QCD vacuum structure
We study the impact of the "intrinsic" hadron transverse momentum on the
pre-asymptotic behavior of the diffractive electroproduction of longitudinally
polarized -meson. Surprisingly, we find the onset of the asymptotic
regime in this problem to be rather low, Q^2 ~ 10 GeV^2 where power corrections
due to the transverse momentum do not exceed 20 % in the amplitude. This
drastically contrasts with exclusive amplitudes where the asymptotics starts at
much higher Q^2 = 50 - 100 GeV^2. The sources of such unexpected behavior are
traced back to some general (the quark-hadron duality) as well as more silent
(properties of higher dimensional vacuum condensates) features of QCD.Comment: 27 pages (LaTex), 1 figure (epsfig
Glueball spectrum in a (1+1)-dimensional model for QCD
We consider (1+1)-dimensional QCD coupled to scalars in the adjoint
representation of the gauge group SU(). This model results from dimensional
reduction of the (2+1)-dimensional pure glue theory. In the large-N limit we
study the spectrum of glueballs numerically, using the discretized \lcq. We
find a discrete spectrum of bound states, with the density of levels growing
approximately exponentially with the mass. A few low-lying states are very
close to being eigenstates of the parton number, and their masses can be
accurately calculated by truncated diagonalizations.Comment: 17 pages, uses phyzzx and table.tex, 5 figures available upon request
from [email protected]
Why is the B -> eta' X decay width so large ?
New mechanism for the observed inclusive B -> \eta'X decay is suggested. We
argue that the dominant contribution to this amplitude is due to the Cabbibo
favored b -> \bar{c}cs process followed by the transition \bar{c}c -> \eta'. A
large magnitude of the "intrinsic charm" component of \eta' is of critical
importance in our approach. Our results are consistent with an unexpectedly
large Br(B -> \eta'+X) \sim 10^{-3} recently announced by CLEO. We stress the
uniqueness of this channel for 0^{-+} gluonia search.Comment: Comments on a mixing model for intrinsic charm and pre-asymptotic
effects and some references are added. Latex, 9 page
Caspase-11 Activation in Response to Bacterial Secretion Systems That Access the Host Cytosol
Inflammasome activation is important for antimicrobial defense because it induces cell death and regulates the secretion of IL-1 family cytokines, which play a critical role in inflammatory responses. The inflammasome activates caspase-1 to process and secrete IL-1β. However, the mechanisms governing IL-1α release are less clear. Recently, a non-canonical inflammasome was described that activates caspase-11 and mediates pyroptosis and release of IL-1α and IL-1β. Caspase-11 activation in response to Gram-negative bacteria requires Toll-like receptor 4 (TLR4) and TIR-domain-containing adaptor-inducing interferon-β (TRIF)-dependent interferon production. Whether additional bacterial signals trigger caspase-11 activation is unknown. Many bacterial pathogens use specialized secretion systems to translocate effector proteins into the cytosol of host cells. These secretion systems can also deliver flagellin into the cytosol, which triggers caspase-1 activation and pyroptosis. However, even in the absence of flagellin, these secretion systems induce inflammasome activation and the release of IL-1α and IL-1β, but the inflammasome pathways that mediate this response are unclear. We observe rapid IL-1α and IL-1β release and cell death in response to the type IV or type III secretion systems of Legionella pneumophila and Yersinia pseudotuberculosis. Unlike IL-1β, IL-1α secretion does not require caspase-1. Instead, caspase-11 activation is required for both IL-1α secretion and cell death in response to the activity of these secretion systems. Interestingly, whereas caspase-11 promotes IL-1β release in response to the type IV secretion system through the NLRP3/ASC inflammasome, caspase-11-dependent release of IL-1α is independent of both the NAIP5/NLRC4 and NLRP3/ASC inflammasomes as well as TRIF and type I interferon signaling. Furthermore, we find both overlapping and non-redundant roles for IL-1α and IL-1β in mediating neutrophil recruitment and bacterial clearance in response to pulmonary infection by L. pneumophila. Our findings demonstrate that virulent, but not avirulent, bacteria trigger a rapid caspase-11-dependent innate immune response important for host defense
-Dimensional Large QCD coupled to Adjoint Fermions
We consider 1+1-dimensional QCD coupled to Majorana fermions in the adjoint
representation of the gauge group . Pair creation of partons (fermion
quanta) is not suppressed in the large- limit, where the glueball-like bound
states become free. In this limit the spectrum is given by a linear \lc\ Schr\"
odinger equation, which we study numerically using the discretized \lcq. We
find a discrete spectrum of bound states, with the logarithm of the level
density growing approximately linearly with the mass. The wave function of a
typical excited state is a complicated mixture of components with different
parton numbers. A few low-lying states, however, are surprisingly close to
being eigenstates of the parton number, and their masses can be accurately
calculated by truncated diagonalizations.Comment: 22 pages + 9 figures (available by request from
[email protected]), uses phyzzx.tex + tables.tex PUPT-1413,
IASSNS-HEP-93/4
Conformal symmetry on the light cone and nonleading twist distribution amplitudes of massive vector meson
A complete set of asymptotic three particle light cone distribution
amplitudes of twist 3 and 4 for a transversely polarized massive vector meson
built out of massless current quarks is constructed. The method used is based
on a modified conformal projectors technique which allows to handle kinematical
corrections due to a finite hadron mass. Consequences of our finding for the
\rho -meson hard diffractive electroproduction and \gamma \rho \pi form factor
are discussed. Our results may imply a breakdown of OPE for some exclusive
processes beyond the leading twist level.Comment: Latex, 12 pages, no figure
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