13 research outputs found
Photon and dilepton emission rates from high density quark matter
We compute the rates of real and virtual photon (dilepton) emission from
dense QCD matter in the color-flavor locked (CFL) phase, focusing on results at
moderate densities (3-5 times the nuclear saturation density) and temperatures
MeV. We pursue two approaches to evaluate the electromagnetic
(e.m.) response of the CFL ground state: (i) a direct evaluation of the photon
self energy using quark particle/-hole degrees of freedom, and (ii) a Hidden
Local Symmetry (HLS) framework based on generalized mesonic excitations where
the meson is introduced as a gauge boson of a local SU(3) color-flavor
group. The coupling to generalized two-pion states induces a finite
width and allows to address the issue of vector meson dominance (VMD) in the
CFL phase. We compare the calculated emissivities (dilepton rates) to those
arising from standard hadronic approaches including in-medium effects. For
rather large superconducting gaps (several tens of MeV at moderate densities),
as suggested by both perturbative and nonperturbative estimates, the dilepton
rates from CFL quark matter turn out to be very similar to those obtained in
hadronic many-body calculations, especially for invariant masses above
GeV. A similar observation holds for (real) photon production.Comment: 18 pages, 12 figure
A renormalisation group approach to two-body scattering in the presence of long-range forces
We apply renormalisation-group methods to two-body scattering by a
combination of known long-range and unknown short-range potentials. We impose a
cut-off in the basis of distorted waves of the long-range potential and
identify possible fixed points of the short-range potential as this cut-off is
lowered to zero. The expansions around these fixed points define the power
countings for the corresponding effective field theories. Expansions around
nontrivial fixed points are shown to correspond to distorted-wave versions of
the effective-range expansion. These methods are applied to scattering in the
presence of Coulomb, Yukawa and repulsive inverse-square potentials.Comment: 22 pages (RevTeX), 4 figure
Efimov physics beyond universality
We provide an exact solution of the Efimov spectrum in ultracold gases within
the standard two-channel model for Feshbach resonances. It is shown that the
finite range in the Feshbach coupling makes the introduction of an adjustable
three-body parameter obsolete. The solution explains the empirical relation
between the scattering length a_- where the first Efimov state appears at the
atom threshold and the van der Waals length l_vdw for open channel dominated
resonances. There is a continuous crossover to the closed channel dominated
limit, where the scale in the energy level diagram as a function of the inverse
scattering length 1/a is set by the intrinsic length r* associated with the
Feshbach coupling. Our results provide a number of predictions for
non-universal ratios between energies and scattering lengths that can be tested
in future experiments.Comment: 6 pages, 4 figures; final versio
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