7,339 research outputs found
Vector meson spectral function and dilepton production rate in a hot and dense medium within an effective QCD approach
The properties of the vector meson current-current correlation function and
its spectral representation are investigated in details with and without
isoscalar-vector interaction within the framework of effective QCD approach,
namely Nambu-Jona-Lasinio (NJL) model and its Polyakov Loop extended version
(PNJL), at finite temperature and finite density. The influence of the
isoscalarvector interaction on the vector meson correlator is obtained using
the ring resummation known as the Random Phase Approximation (RPA). The
spectral as well as the correlation function in PNJL model show that the vector
meson retains its bound property up to a moderate value of temperature above
the phase transition. Using the vector meson spectral function we, for the
first time, obtained the dilepton production rate from a hot and dense medium
within the framework of PNJL model that takes into account the nonperturbative
effect through the Polyakov Loop fields. The dilepton production rate in PNJL
model is enhanced compared to NJL and Born rate in the deconfined phase due to
the suppression of color degrees of freedom at moderate temperature. The
presence of isoscalar-vector interaction further enhances the dileption rate
over the Born rate in the low mass region. Further, we also have computed the
Euclidean correlation function in vector channel and the conserved density
fluctuation associated with temporal correlation function appropriate for a hot
and dense medium. The dilepton rate and the Euclidean correlator are also
compared with available lattice data and those quantities in PNJL model are
found to agree well in certain domain.Comment: 30 pages, 16 figures, typos corrected, references added, to appear in
JHE
Elastic energy loss and longitudinal straggling of a hard jet
The elastic energy loss encountered by jets produced in deep-inelastic
scattering (DIS) off a large nucleus is studied in the collinear limit. In
close analogy to the case of (non-radiative) transverse momentum broadening,
which is dependent on the medium transport coefficient , a class of
medium enhanced higher twist operators which contribute to the non-radiative
loss of the forward light-cone momentum of the jet () are identified and
the leading correction in the limit of asymptotically high is isolated.
Based on these operator products, a new transport coefficient is
motivated which quantifies the energy loss per unit length encountered by the
hard jet. These operator products are then computed, explicitly, in the case of
a similar hard jet traversing a deconfined quark-gluon-plasma (QGP) in the
hard-thermal-loop (HTL) approximation. This is followed by an evaluation of
sub-leading contributions which are suppressed by the light-cone momentum
, which yields the longitudinal "straggling" i.e., a slight change in
light cone momentum due to the Brownian propagation through a medium with a
fluctuating color field.Comment: 5 pages, 1 figure, Revtex
Orientifolds of type IIA strings on Calabi-Yau manifolds
We identify type IIA orientifolds that are dual to M-theory compactifications
on manifolds with G_2-holonomy. We then discuss the construction of crosscap
states in Gepner models. (Based on a talk presented by S.G. at PASCOS 2003 held
at the Tata Institute of Fundamental Research, Mumbai during Jan. 3-8, 2003.)Comment: 3 pages, RevTeX, PASCOS '03 tal
Universality in Fluid Domain Coarsening: The case of vapor-liquid transition
Domain growth during the kinetics of phase separation is studied following
vapor-liquid transition in a single component Lennard-Jones fluid. Results are
analyzed after appropriately mapping the continuum snapshots obtained from
extensive molecular dynamics simulations to a simple cubic lattice. For near
critical quench interconnected domain morphology is observed. A brief period of
slow diffusive growth is followed by a linear viscous hydrodynamic growth that
lasts for an extended period of time. This result is in contradiction with
earlier inclusive reports of late time growth exponent 1/2 that questions the
uniqueness of the non-equilibrium universality for liquid-liquid and
vapor-liquid transitions.Comment: 6 pages, 5 figure
Energy and momentum deposited into a QCD medium by a jet shower
Hard partons moving through a dense QCD medium lose energy by radiative
emissions and elastic scatterings. Deposition of the radiative contribution
into the medium requires rescattering of the radiated gluons. We compute the
total energy loss and its deposition into the medium self-consistently within
the same formalism, assuming perturbative interaction between probe and medium.
The same transport coefficients that control energy loss of the hard parton
determine how the energy is deposited into the medium; this allows a parameter
free calculation of the latter once the former have been computed or extracted
from experimental energy loss data. We compute them for a perturbative medium
in hard thermal loop (HTL) approximation. Assuming that the deposited
energy-momentum is equilibrated after a short relaxation time, we compute the
medium's hydrodynamical response and obtain a conical pattern that is strongly
enhanced by showering.Comment: 4 pages, 3 figures, revtex4, intro modified, typos correcte
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