1,136 research outputs found
The non-Abelian feature of parton energy loss in energy dependence of jet quenching in high-energy heavy-ion collisions
One of the non-Abelian features of parton energy loss is the ratio between gluon and quark jets. Since jet production rate is
dominated by quark jets at high and by gluon jets at low
, high hadron suppression in high-energy heavy-ion collisions should
reflect such a non-Abelian feature. Within a leading order perturbative QCD
parton model that incorporates transverse expansion and Woods-Saxon nuclear
distribution, the energy dependence of large GeV/ hadron
suppression is found to be sensitive to the non-Abelian feasture of parton
energy loss and could be tested by data from low energy runs at RHIC or data
from LHC.Comment: RevTex 4, 7 pages, 3 figure
Azimuthal and single spin asymmetry in deep-inelastic lepton-nucleon scattering
We derive a general framework for describing semi-inclusive deep-inelastic
lepton-nucleon scattering in terms of the unintegrated parton distributions and
other higher twist parton correlations. Such a framework provides a consistent
approach to the calculation of inclusive and semi-inclusive cross sections
including higher twist effects. As an example, we calculate the azimuthal
asymmetries to the order of 1/Q in semi-inclusive process with transversely
polarized target. A non-vanishing single-spin asymmetry in the ``triggered
inclusive process'' is predicted to be 1/Q suppressed with a part of the
coefficient related to a moment of the Sivers function.Comment: 9 pages, 1 figur
Globally Polarized Quark-gluon Plasma in Non-central A+A Collisions
Produced partons have large local relative orbital angular momentum along the
direction opposite to the reaction plane in the early stage of non-central
heavy-ion collisions. Parton scattering is shown to polarize quarks along the
same direction due to spin-orbital coupling. Such global quark polarization
will lead to many observable consequences, such as left-right asymmetry of
hadron spectra, global transverse polarization of thermal photons, dileptons
and hadrons. Hadrons from the decay of polarized resonances will have azimuthal
asymmetry similar to the elliptic flow. Global hyperon polarization is
predicted within different hadronization scenarios and can be easily tested.Comment: 4 pages in RevTex with 2 postscript figures, an erratum is added to
the final published versio
Dependency Stochastic Boolean Satisfiability: A Logical Formalism for NEXPTIME Decision Problems with Uncertainty
Stochastic Boolean Satisfiability (SSAT) is a logical formalism to model
decision problems with uncertainty, such as Partially Observable Markov
Decision Process (POMDP) for verification of probabilistic systems. SSAT,
however, is limited by its descriptive power within the PSPACE complexity
class. More complex problems, such as the NEXPTIME-complete Decentralized POMDP
(Dec-POMDP), cannot be succinctly encoded with SSAT. To provide a logical
formalism of such problems, we extend the Dependency Quantified Boolean Formula
(DQBF), a representative problem in the NEXPTIME-complete class, to its
stochastic variant, named Dependency SSAT (DSSAT), and show that DSSAT is also
NEXPTIME-complete. We demonstrate the potential applications of DSSAT to
circuit synthesis of probabilistic and approximate design. Furthermore, to
study the descriptive power of DSSAT, we establish a polynomial-time reduction
from Dec-POMDP to DSSAT. With the theoretical foundations paved in this work,
we hope to encourage the development of DSSAT solvers for potential broad
applications.Comment: 10 pages, 5 figures. A condensed version of this work is published in
the AAAI Conference on Artificial Intelligence (AAAI) 202
Modified Fragmentation Function from Quark Recombination
Within the framework of the constituent quark model, it is shown that the
single hadron fragmentation function of a parton can be expressed as a
convolution of shower diquark or triquark distribution function and quark
recombination probability, if the interference between amplitudes of quark
recombination with different momenta is neglected. The recombination
probability is determined by the hadron's wavefunction in the constituent quark
model. The shower diquark or triquark distribution functions of a fragmenting
jet are defined in terms of overlapping matrices of constituent quarks and
parton field operators. They are similar in form to dihadron or trihadron
fragmentation functions in terms of parton operator and hadron states.
Extending the formalism to the field theory at finite temperature, we
automatically derive contributions to the effective single hadron fragmentation
function from the recombination of shower and thermal constituent quarks. Such
contributions involve single or diquark distribution functions which in turn
can be related to diquark or triquark distribution functions via sum rules. We
also derive QCD evolution equations for quark distribution functions that in
turn determine the evolution of the effective jet fragmentation functions in a
thermal medium.Comment: 23 pages in RevTex with 8 postscript figure
Jet Tomography of Hot and Cold Nuclear Matter
Medium modification of parton fragmentation functions induced by multiple
scattering and gluon bremsstrahlung is shown to describe the recent HERMES data
in deeply inelastic scattering (DIS) very well, providing the first evidence of
-dependence of the modification. The energy loss is found to be
GeV/fm for a 10-GeV quark in a nucleus. Including
the effect of expansion, analysis of the spectra in central
collisions at GeV yields an averaged energy loss equivalent to
GeV/fm in a static medium. Predictions for central
collisions at GeV are also given.Comment: 4 pages in RevTex with 3 ps figures, final version published in Phys.
Rev. Letter
Do Search for Dibaryonic De - Excitations in Relativistic Nuclear Reactions
Some odd characteristics are observed in the single particle distributions
obtained from interactions at momenta which are
explained as the manifestation of a new mechanism of strangeness production via
dibaryonic de-excitations. A signature of the formation of hadronic and
baryonic clusters is also reported. The di-pionic signals of the dibaryonic
orbital de-excitations are analyzed in the frame of the MIT - bag Model and a
Monte Carlo simulation.The role played by the dibaryonic resonances in
relativistic nuclear collisions could be a significant one.
Key words: Relativistic nuclear interactions negative pions, negative kaons,
di-pions , streamer chamber, dibaryons, MIT - bag model
PACS codes: 25.75.+r,14.40.Aq,14.20.Pt,12.40.AsComment: 17 pages,LATEX, preprint ICTP -243 1993,figures available by reques
Strangeness Enhancement in and Interactions at SPS Energies
The systematics of strangeness enhancement is calculated using the HIJING and
VENUS models and compared to recent data on , and
collisions at CERN/SPS energies (). The HIJING model is used to
perform a {\em linear} extrapolation from to . VENUS is used to
estimate the effects of final state cascading and possible non-conventional
production mechanisms. This comparison shows that the large enhancement of
strangeness observed in collisions, interpreted previously as possible
evidence for quark-gluon plasma formation, has its origins in non-equilibrium
dynamics of few nucleon systems. % Strangeness enhancement %is therefore traced
back to the change in the production dynamics %from to minimum bias
and central collisions. A factor of two enhancement of at
mid-rapidity is indicated by recent data, where on the average {\em one}
projectile nucleon interacts with only {\em two} target nucleons. There appears
to be another factor of two enhancement in the light ion reaction relative
to , when on the average only two projectile nucleons interact with two
target ones.Comment: 29 pages, 8 figures in uuencoded postscript fil
HDAC8 and STAT3 Repress BMF Gene Activity in Colon Cancer Cells
Histone deacetylase (HDAC) inhibitors are undergoing clinical trials as anticancer agents, but some exhibit resistance mechanisms linked to anti-apoptotic Bcl-2 functions, such as BH3-only protein silencing. HDAC inhibitors that reactivate BH3-only family members might offer an improved therapeutic approach. We show here that a novel seleno-α-keto acid triggers global histone acetylation in human colon cancer cells and activates apoptosis in a p21-independent manner. Profiling of multiple survival factors identified a critical role for the BH3-only member Bcl-2-modifying factor (Bmf). On the corresponding BMF gene promoter, loss of HDAC8 was associated with signal transducer and activator of transcription 3 (STAT3)/specificity protein 3 (Sp3) transcription factor exchange and recruitment of p300. Treatment with a p300 inhibitor or transient overexpression of exogenous HDAC8 interfered with BMF induction, whereas RNAi-mediated silencing of STAT3 activated the target gene. This is the first report to identify a direct target gene of HDAC8 repression, namely, BMF. Interestingly, the repressive role of HDAC8 could be uncoupled from HDAC1 to trigger Bmf-mediated apoptosis. These findings have implications for the development of HDAC8-selective inhibitors as therapeutic agents, beyond the reported involvement of HDAC8 in childhood malignancy
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