195,627 research outputs found
Toward parton equilibration with improved parton interaction matrix elements
The Quark-Gluon Plasma can be produced in high energy heavy ion collisions
and how it equilibrates is important for the extraction of the properties of
strongly interacting matter. A radiative transport model can be used to reveal
interesting characteristics of Quark-Gluon Plasma thermalization. For example,
screened parton interactions always lead to partial pressure isotropization.
Systems with different initial pressure anisotropies evolve toward the same
asymptotic evolution. In particular, radiative processes are crucial for the
chemical equilibration of the system. Matrix elements under the soft and
collinear approximation for these processes, as first derived by Gunion and
Bertsch, are widely used. A different approach is to start with the exact
matrix elements for the two to three and its inverse processes. General
features of this approach will be reviewed and the results will be compared
with the Gunion-Bertsch results. We will comment on the possible implications
of the exact matrix element approach on Quark-Gluon Plasma thermalization.Comment: Presented at the 11th International Conference on Nucleus-Nucleus
Collisions (NN2012), San Antonio, Texas, USA, 27 May-1 June 201
Jet conversions in a quark-gluon plasma
Quark and gluon jets traversing through a quark-gluon plasma not only lose
their energies but also can undergo flavor conversions. The conversion rates
via the elastic and the inelastic scatterings are evaluated in the lowest order in QCD.
Including both jet energy loss and conversions in the expanding quark-gluon
plasma produced in relativistic heavy ion collisions, we have found a net
conversion of quark to gluon jets. This reduces the difference between the
nuclear modification factors for quark and gluon jets in central heavy ion
collisions and thus enhances the and ratios at high
transverse momentum. However, a much larger net quark to gluon jet conversion
rate than the one given by the lowest-order QCD is needed to account for the
observed similar ratios in central Au+Au and p+p collisions at same energy.
Implications of our results are discussed.Comment: version to appear in PR
Effective charge and free energy of DNA inside an ion channel
Translocation of a single stranded DNA (ssDNA) through an alpha-hemolysin
channel in a lipid membrane driven by applied transmembrane voltage V was
extensively studied recently. While the bare charge of the ssDNA piece inside
the channel is approximately 12 (in units of electron charge) measurements of
different effective charges resulted in values between one and two. We explain
these challenging observations by a large self-energy of a charge in the narrow
water filled gap between ssDNA and channel walls, related to large difference
between dielectric constants of water and lipid, and calculate effective
charges of ssDNA. We start from the most fundamental stall charge , which
determines the force stalling DNA against the voltage V (L is
the length of the channel). We show that the stall charge is proportional
to the ion current blocked by DNA, which is small due to the self-energy
barrier. Large voltage V reduces the capture barrier which DNA molecule should
overcome in order to enter the channel by , where is the
effective capture charge. We expressed it through the stall charge . We
also relate the stall charge to two other effective charges measured for
ssDNA with a hairpin in the back end: the charge responsible for
reduction of the barrier for unzipping of the hairpin and the charge
responsible for DNA escape in the direction of hairpin against the voltage. At
small V we explain reduction of the capture barrier with the salt
concentration.Comment: Typos are correcte
FLIC Overlap Fermions
The action of the overlap-Dirac operator on a vector is typically implemented
indirectly through a multi-shift conjugate gradient solver. The compute-time
required depends upon the condition number, , of the matrix that is
used as the overlap kernel. While the Wilson action is typically used as the
overlap kernel, the FLIC (Fat Link Irrelevant Clover) action has an improved
condition number and provides up to a factor of two speedup in evaluating the
overlap action. We summarize recent progress on the use of FLIC overlap
fermions.Comment: Lattice2002(chiral
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