6,192 research outputs found
General structure of gauge boson propagator and its spectra in a hot magnetized medium
Based on transversality condition of gauge boson self-energy we have
systematically constructed the general structure of the gauge boson two-point
functions using four linearly independent basis tensors in presence of a
nontrivial background, i.e., hot magnetized material medium. The hard thermal
loop approximation has been used for the heat bath to compute various form
factors associated with the gauge boson's two point functions both in strong
and weak field approximation. We have also analyzed the dispersion of a gauge
boson (e.g., gluon) using the effective propagator both in strong and weak
magnetic field approximation. The formalism is also applicable to QED. The
presence of only thermal background leads to a longitudinal (plasmon) mode and
a two-fold degenerate transverse mode. In presence of a hot magnetized
background medium the degeneracy of the two transverse modes is lifted and one
gets three quasiparticle modes. In weak field approximation one gets two
transverse modes and one plasmon mode. On the other hand, in strong field
approximation also one gets the three modes in Lowest Landau Level. The general
structure of two-point function may be useful for computing the thermo-magnetic
correction of various quantities associated with a gauge boson.Comment: 39 pages, 7 figure
Quark Number Susceptibility and Thermodynamics in HTL approximation
In HTL perturbation theory we obtain leading order quark number
susceptibility as a response to an external disturbance, viz., chemical
potential (\mu) that generates density fluctuation, which is related to the
correlation function through the thermodynamic sum rule associated with the
symmetry of the system. We also obtain various thermodynamic quantities in
leading order.Comment: 4 pages, 2 figures, Talk given at the 6th ICPAQGP-2010, Goa, India,
December 6-10, 201
Wavepacket dynamics on Chern band lattices in a trap
The experimental realization of lattices with Chern bands in ultracold-atom
and photonic systems has motivated the study of time-dependent phenomena, such
as spatial propagation, in lattices with nontrivial topology. We study the
dynamics of gaussian wavepackets on the Haldane honeycomb Chern-band lattice
model, in the presence of a harmonic trap. We focus on the transverse response
to a force, which is due partly to the Berry curvature and partly to the
transverse component of the energy band curvature. We evaluate the accuracy of
a semiclassical description, which treats the wavepacket as a point particle in
both real and momentum space, in reproducing the motion of a realistic
wavepacket with finite extent. We find that, in order to accurately capture the
wavepacket dynamics, the extent of the wavepacket in momentum space needs to be
taken into account. The dynamics is sensitive to the interplay of band
dispersion and Berry curvature over the finite region of momentum (reciprocal)
space where the wavepacket has support. Moreover, if the wavepacket is prepared
with a finite initial momentum, the semiclassical analysis reproduces its
motion as long as it has a large overlap with the eigenstates of a single band.
The semiclassical description generally improves with increasing real-space
size of the wavepacket, as long as the external conditions (e.g., external
force) remain uniform throughout the spatial extent of the wavepacket.Comment: 11 pages, 8 figures, typos corrected, version published in Phys. Rev.
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
Toxicity induced by Solanapyrone A in Chickpea shoots and its metabolism through Glutathione/Glutathione-S-Transferase system
Solanapyrone A and C were isolated from a Pakistani isolate of Ascochyta rabiei, Pk-1. Two experiments were conducted to investigate the phytotoxic effects of the most potent toxin, solanapyrone A on chickpea cultivars and its subsequent detoxification through glutathion/glutathion-s-transferase(GST) system. When the shoots of cultivars were fed solanapyrone A, symptoms mimicking to Ascochyta blight appeared and extent of manifestation of symptoms varied with the cultivar. In the first experiment, the effect of three different plant ages of 2 cultivars with different levels of resistance to toxin was determined in terms of GST activity unit. GST activity in Balkasar-2000 (a resistant cultivar) increased 1.92 times, 1.72 and 1.65 times in two-week-old seedling, eight-week-old and adult plants (all treated) respectively as compared to their respective controls. In the highly susceptible cultivar, AUG-424, a slight increase (1.14 times) over control was noticed in GST activity at all the three ages. In the second experiment, where shoots of three cultivars were tested against 2 doses of the toxin, an increase in GST activity in Noor-91 (a moderately susceptible cultivar) and AUG-424 was significantly less than resistant cultivar, Balkasar-2000 showing direct relationship between resistance and activity of the enzyme. It may be concluded that it is a reason for difference in response of cultivars to the disease
- …