131 research outputs found
The deconfined phase near Tc and its decay into hadrons
We sketch an effective theory for the deconfined state of QCD near Tc. This
relates the behavior of the expectation value of the Polyakov loop, and its
two-point functions, to the pressure. Defining the ``mass'' of three and two
gluon states from the imaginary and real parts of the Polyakov loop, while this
ratio is 3:2 in perturbation theory, at Tc it is 3:1. We also discuss the decay
of the deconfined state into hadrons.Comment: 4 pages, no figures, Contribution to the Proceedings of "Quark Matter
2002", Nantes, France, 18-24 Jul 200
Transverse Momentum in Semi-Inclusive Polarized Deep Inelastic Scattering and the Spin-Flavor Structure of the Proton
The non-valence spin-flavor structure of the nucleon extracted from
semi-inclusive measurements of polarized deep inelastic scattering depends
strongly on the transverse momentum of the detected hadrons which are used to
determine the individual polarized sea distributions. This physics may explain
the recent HERMES observation of a positively polarized strange sea through
semi-inclusive scattering, in contrast to the negative strange sea polarization
deduced from inclusive polarized deep inelastic scattering.Comment: 4 pages, revtex style, 2 figure
Gauge symmetry and the EMC spin effect
We emphasise the EMC spin effect as a problem of symmetry and discuss the
renormalisation of the axial tensor operators. This involves the
generalisation of the Adler-Bell-Jackiw anomaly to each of these operators. We
find that the contribution of the axial anomaly to the spin dependent structure
function scales at . This means that the anomaly
can be a large effect in . Finally we discuss the jet signature of the
anomaly.Comment: 17 pages, Latex, Cavendish preprint HEP 93/
Dynamical Renormalization Group Approach to Quantum Kinetics in Scalar and Gauge Theories
We derive quantum kinetic equations from a quantum field theory implementing
a diagrammatic perturbative expansion improved by a resummation via the
dynamical renormalization group. The method begins by obtaining the equation of
motion of the distribution function in perturbation theory. The solution of
this equation of motion reveals secular terms that grow in time, the dynamical
renormalization group resums these secular terms in real time and leads
directly to the quantum kinetic equation. We used this method to study the
relaxation in a cool gas of pions and sigma mesons in the O(4) chiral linear
sigma model. We obtain in relaxation time approximation the pion and sigma
meson relaxation rates. We also find that in large momentum limit emission and
absorption of massless pions result in threshold infrared divergence in sigma
meson relaxation rate and lead to a crossover behavior in relaxation. We then
study the relaxation of charged quasiparticles in scalar electrodynamics
(SQED). While longitudinal, Debye screened photons lead to purely exponential
relaxation, transverse photons, only dynamically screened by Landau damping
lead to anomalous relaxation, thus leading to a crossover between two different
relaxational regimes. We emphasize that infrared divergent damping rates are
indicative of non-exponential relaxation and the dynamical renormalization
group reveals the correct relaxation directly in real time. Finally we also
show that this method provides a natural framework to interpret and resolve the
issue of pinch singularities out of equilibrium and establish a direct
correspondence between pinch singularities and secular terms. We argue that
this method is particularly well suited to study quantum kinetics and transport
in gauge theories.Comment: RevTeX, 40 pages, 4 eps figures, published versio
Thermal fluctuations in the interacting pion gas
We derive the two-particle fluctuation correlator in a thermal gas of
pi-mesons to the lowest order in an interaction due to a resonance exchange. A
diagrammatic technique is used. We discuss how this result can be applied to
event-by-event fluctuations in heavy-ion collisions, in particular, to search
for the critical point of QCD. As a practical example, we determine the shape
of the rapidity correlator.Comment: 12 pages, 4 figures, RevTe
Electromagnetic probes
We introduce the seminal developments in the theory and experiments of
electromagnetic probes for the study of the dynamics of relativistic heavy ion
collisions and quark gluon plasma.Comment: 47 pages, 33 Figures; Lectures delivered by Dinesh K. Srivastava at
QGP Winter School (QGPWS08) at Jaipur, India, February 1-3, 200
Chiral Analysis of Quenched Baryon Masses
We extend to quenched QCD an earlier investigation of the chiral structure of
the masses of the nucleon and the delta in lattice simulations of full QCD.
Even after including the meson-loop self-energies which give rise to the
leading and next-to-leading non-analytic behaviour (and hence the most rapid
variation in the region of light quark mass), we find surprisingly little
curvature in the quenched case. Replacing these meson-loop self-energies by the
corresponding terms in full QCD yields a remarkable level of agreement with the
results of the full QCD simulations. This comparison leads to a very good
understanding of the origins of the mass splitting between these baryons.Comment: 23 pages, 6 figure
Space-time evolution and HBT analysis of relativistic heavy ion collisions in a chiral SU(3) x SU(3) model
The space-time dynamics and pion-HBT radii in central heavy ion-collisions at
CERN-SPS and BNL-RHIC are investigated within a hydrodynamic simulation. The
dependence of the dynamics and the HBT-parameters on the EoS is studied with
different parametrisations of a chiral SU(3) sigma-omega model. The
selfconsistent collective expansion includes the effects of effective hadron
masses, generated by the nonstrange and strange scalar condensates. Different
chiral EoS show different types of phase transitions and even a crossover. The
influence of the order of the phase transition and of the difference in the
latent heat on the space-time dynamics and pion-HBT radii is studied. A small
latent heat, i.e. a weak first-order chiral phase transition, or even a smooth
crossover leads to distinctly different HBT predictions than a strong first
order phase transition. A quantitative description of the data, both at SPS
energies as well as at RHIC energies, appears difficult to achieve within the
ideal hydrodynamical approach using the SU(3) chiral EoS. A strong first-order
quasi-adiabatic chiral phase transition seems to be disfavored by the pion-HBT
data from CERN-SPS and BNL-RHIC
Spin structure of the nucleon: QCD evolution, lattice results and models
The question how the spin of the nucleon is distributed among its quark and
gluon constituents is still a subject of intense investigations. Lattice QCD
has progressed to provide information about spin fractions and orbital angular
momentum contributions for up- and down-quarks in the proton, at a typical
scale \mu^2~4 GeV^2. On the other hand, chiral quark models have traditionally
been used for orientation at low momentum scales. In the comparison of such
model calculations with experiment or lattice QCD, fixing the model scale and
the treatment of scale evolution are essential. In this paper, we present a
refined model calculation and a QCD evolution of lattice results up to
next-to-next-to-leading order. We compare this approach with the Myhrer-Thomas
scenario for resolving the proton spin puzzle.Comment: 11 pages, 6 figures, equation (9) has been corrected leading to a
revised figure 1b. Revision matches published versio
Breathing Current Domains in Globally Coupled Electrochemical Systems: A Comparison with a Semiconductor Model
Spatio-temporal bifurcations and complex dynamics in globally coupled
intrinsically bistable electrochemical systems with an S-shaped current-voltage
characteristic under galvanostatic control are studied theoretically on a
one-dimensional domain. The results are compared with the dynamics and the
bifurcation scenarios occurring in a closely related model which describes
pattern formation in semiconductors. Under galvanostatic control both systems
are unstable with respect to the formation of stationary large amplitude
current domains. The current domains as well as the homogeneous steady state
exhibit oscillatory instabilities for slow dynamics of the potential drop
across the double layer, or across the semiconductor device, respectively. The
interplay of the different instabilities leads to complex spatio-temporal
behavior. We find breathing current domains and chaotic spatio-temporal
dynamics in the electrochemical system. Comparing these findings with the
results obtained earlier for the semiconductor system, we outline bifurcation
scenarios leading to complex dynamics in globally coupled bistable systems with
subcritical spatial bifurcations.Comment: 13 pages, 11 figures, 70 references, RevTex4 accepted by PRE
http://pre.aps.or
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