14,320 research outputs found
Parton Production Via Vacuum Polarization
We discuss the production mechanism of partons via vacuum polarization during
the very early, gluon dominated phase of an ultrarelativistic heavy-ion
collision in the framework of the background field method of quantum
chromodynamics.Comment: 3 pages, Latex, 3 figures (eps), to be published in JPhysG, SQM2001
proceeding
Fragmentation Function in Non-Equilibrium QCD Using Closed-Time Path Integral Formalism
In this paper we implement Schwinger-Keldysh closed-time path integral
formalism in non-equilibrium QCD to the definition of Collins-Soper
fragmentation function. We consider a high p_T parton in QCD medium at initial
time t_0 with arbitrary non-equilibrium (non-isotropic) distribution function
f(\vec{p}) fragmenting to hadron. We formulate parton to hadron fragmentation
function in non-equilibrium QCD in the light-cone quantization formalism. It
may be possible to include final state interactions with the medium via
modification of the Wilson lines in this definition of the non-equilibrium
fragmentation function. This may be relevant to study hadron production from
quark-gluon plasma at RHIC and LHC.Comment: 15 pages latex, Accepted for Publication in European Physical Journal
Color Octet Contribution to High p_T J/\Psi Production in pp Collisions at \sqrt s = 500 and 200 GeV at RHIC
We compute \frac{d\sigma}{dp_T} of the J/\psi production in pp collisions at
RHIC at \sqrt s = 500 and 200 GeV by using both the color octet and singlet
models in the framework of non-relativistic QCD. The J/\psi we compute here
includes the direct J/\psi from the partonic fusion processes and the J/\psi
coming from the radiative decays of \chi_J's both in the color octet and
singlet channel. The high p_T J/\psi production cross section is computed
within the PHENIX detector acceptance ranges: -0.35 < \eta < 0.35 and 1.2 <
\|\eta| < 2.4, the central electron and forward muon arms. It is found that the
color octet contribution to J/\psi production is dominant at RHIC energy in
comparison to the color singlet contributions. We compare our results with the
recent preliminary data obtained by PHENIX detector for the high p_T J/\psi
measurements. While the color singlet model fails to explain the data
completely the color octet model is in agreement with the single data point
above 2 GeV transverse momentum. A measurement of J/\psi production at RHIC in
the next run with better statistics will allow us to determine the validity of
the color octet model of J/\psi production at RHIC energies. This is very
important because it is necessary to know the exact mechanism for J/\psi
production in pp collisions at RHIC if one is to make predictions of J/\psi
suppression as a signature of quark-gluon plasma. These mechanisms also play an
important role in determining the polarized spin structure function of the
proton at RHIC.Comment: 16 pages latex, 6 figure
Production and Equilibration of the Quark-Gluon Plasma with Chromoelectric Field and Minijets
Production and equilibration of quark-gluon plasma are studied within the
color flux-tube model, at the RHIC and LHC energies. Non-Abelian relativistic
transport equations for quarks, antiquarks and gluons, are solved in the
extended phase space which includes coordinates, momenta and color. Before the
chromoelectric field is formed, hard and semihard partons are produced via
minijets which provide the initial conditions necessary to solve the transport
equations. The model predicts that in spite of the vast difference between the
RHIC and LHC incident energies, once the local equilibrium is reached, the
energy densities, the number densities and the temperatures at the two machines
may not be very different from each other. The minijet input significantly
alters the evolution of the deconfined matter, unless the color field is too
strong. For the input parameters used here the equilibration time is estimated
to be fm at RHIC and fm at LHC, measured from the instant
when the two colliding nuclei have just passed through each other. The
temperature at equilibration is found to be MeV at RHIC and MeV at LHC.Comment: version to appear in Phys. Rev. C; discussion enlarged to include
comparison with other models; conclusions unchanged; 14 single-spaced pages +
8 ps figure
Schwinger Mechanism for Gluon Pair Production in the Presence of Arbitrary Time Dependent Chromo-Electric Field
We study Schwinger mechanism for gluon pair production in the presence of
arbitrary time-dependent chromo-electric background field with
arbitrary color index =1,2,...8 in SU(3) by directly evaluating the path
integral. We obtain an exact expression for the probability of non-perturbative
gluon pair production per unit time per unit volume and per unit transverse
momentum from arbitrary . We show that the
tadpole (or single gluon) effective action does not contribute to the
non-perturbative gluon pair production rate . We find
that the exact result for non-perturbative gluon pair production is independent
of all the time derivatives where
and has the same functional dependence on two casimir invariants
and as the constant
chromo-electric field result with the replacement: . This
result may be relevant to study the production of a non-perturbative
quark-gluon plasma at RHIC and LHC.Comment: 13 pages latex, Published in European Physical Journal
Altarelli-Parisi Equation in Non-Equilibrium QCD
The evolution of fragmentation function in non-equilibrium QCD by using
DGLAP evolution equation may be necessary to study hadron formation from
quark-gluon plasma at RHIC and LHC. In this paper we study splitting functions
in non-equilibrium QCD by using Schwinger-Keldysh closed-time path integral
formalism. For quarks and gluons with arbitrary non-equilibrium distribution
functions and , we derive expressions for quark
and gluon splitting functions in non-equilibrium QCD at leading order in
. We make a comparison of these splitting functions with that
obtained by Altarelli and Parisi in vacuum.Comment: QCD Evolution Time vs Non-Equilibrium Relaxation Time Added, 13 pages
latex, Final Version to be Published in Phys. Part. Nucl. V.43, N6 (2012).
arXiv admin note: text overlap with arXiv:0808.128
O(4)-Invariant Formulation of the Nodal Liquid
We consider the O(4) symmetric point in the phase diagram of an electron
system in which there is a transition between d_{x^2 - y^2} density-wave order
and d_{x^2 - y^2} superconductivity. If the pseudospin
symmetry is disordered by quantum fluctuations, the Nodal Liquid can result. In
this context, we (1) construct a pseudospin -model; (2) discuss its
topological excitations; (3) point out the possibility of a {\it
pseudospin-Peierls} state and (4) propose a phase diagram for the underdoped
cuprate superconductors
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