2,718 research outputs found
Ward Identities in Non-equilibrium QED
We verify the QED Ward identity for the two- and three -point functions at
non-equilibrium in the HTL limit. We use the Keldysh formalism of real time
finite temperature field theory. We obtain an identity of the same form as the
Ward identity for a set of one loop self-energy and one loop three-point vertex
diagrams which are constructed from HTL effective propagators and vertices.Comment: 19 pages, RevTex, 4 PostScript figures, revised version to be
published in Phys. Rev.
The Quark-Gluon-Plasma Liquid
The quark-gluon plasma close to the critical temperature is a strongly
interacting system. Using strongly coupled, classical, non-relativistic plasmas
as an analogy, we argue that the quark-gluon plasma is in the liquid phase.
This allows to understand experimental observations in ultrarelativistic
heavy-ion collisions and to interpret lattice QCD results. It also supports the
indications of the presence of a strongly coupled QGP in ultrarelativistic
heavy-ion collisions.Comment: 8 pages, 2 figures, final version, to bepublished in J. Phys.
Large harmonic softening of the phonon density of states of uranium
Phonon density-of-states curves were obtained from inelastic neutron scattering spectra from the three crystalline phases of uranium at temperatures from 50 to 1213 K. The alpha -phase showed an unusually large thermal softening of phonon frequencies. Analysis of the vibrational power spectrum showed that this phonon softening originates with the softening of a harmonic solid, as opposed to vibrations in anharmonic potentials. It follows that thermal excitations of electronic states are more significant thermodynamically than are the classical volume effects. For the alpha-beta and beta-gamma phase transitions, vibrational and electronic entropies were comparable
Cherenkov radiation by particles traversing the background radiatio n
High energy particles traversing the Universe through the cosmic microwave
backgroung radiation can, in principle, emit Cherenkov radiation. It is shown
that the energy threshold for this radiation is extremely high and its
intensity would be too low due to the low density of the "relic photons gas"
and very weak interaction of two photons.Comment: 6 pages, LATEX, no Figs.; to be published in JETP Lett. 75 (N4)
(2002
Covariant transport approach for strongly interacting partonic systems
The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus
collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD)
transport approach, which is based on a dynamical quasiparticle model for
partons (DQPM) matched to reproduce recent lattice-QCD results - including the
partonic equation of state - in thermodynamic equilibrium. Scalar- and
vector-interaction densities are extracted from the DQPM as well as effective
scalar- and vector-mean fields for the partons. The transition from partonic to
hadronic degrees of freedom is described by covariant transition rates for the
fusion of quark-antiquark pairs or three quarks (antiquarks), respectively,
obeying flavor current-conservation, color neutrality as well as
energy-momentum conservation. Since the dynamical quarks and antiquarks become
very massive close to the phase transition, the formed resonant 'pre-hadronic'
color-dipole states ( or ) are of high invariant mass, too, and
sequentially decay to the groundstate meson and baryon octets increasing the
total entropy. When applying the PHSD approach to Pb+Pb colllisions at 158
AGeV we find a significant effect of the partonic phase on the
production of multi-strange antibaryons due to a slightly enhanced
pair production from massive time-like gluon decay and a larger formation of
antibaryons in the hadronization process.Comment: 12 pages, 6 figures, to be published in the Proceedings of the 26th
Winter Workshop on `Nuclear Dynamics', Ochto Rios, Jamaica, 2-9 January,
2010
Multiparticle production in the Glasma at NLO and plasma instabilities
We discuss the relation between multi-particle production in the Glasma at
next-to-leading order and the physics of plasma instabilities.Comment: 4 pages, talk at Quark Matter 200
Wakes in the quark-gluon plasma
Using the high temperature approximation we study, within the linear response
theory, the wake in the quark-gluon plasma by a fast parton owing to dynamical
screening in the space like region. When the parton moves with a speed less
than the average speed of the plasmon, we find that the wake structure
corresponds to a screening charge cloud traveling with the parton with one sign
flip in the induced charge density resulting in a Lennard-Jones type potential
in the outward flow with a short range repulsive and a long range attractive
part. On the other hand if the parton moves with a speed higher than that of
plasmon, the wake structure in the induced charge density is found to have
alternate sign flips and the wake potential in the outward flow oscillates
analogous to Cerenkov like wave generation with a Mach cone structure trailing
the moving parton. The potential normal to the motion of the parton indicates a
transverse flow in the system. We also calculate the potential due to a color
dipole and discuss consequences of possible new bound states and
suppression in the quark-gluon plasma.Comment: 20 pages, 14 figures (high resolution figures available with
authors); version accepted for publication in Phys. Rev.
First Results from Viper: Detection of Small-Scale Anisotropy at 40 GHZ
Results of a search for small-scale anisotropy in the cosmic microwave
background (CMB) are presented. Observations were made at the South Pole using
the Viper telescope, with a .26 degree (FWHM) beam and a passband centered at
40 GHz. Anisotropy band-power measurements in bands centered at l = 108, 173,
237, 263, 422 and 589 are reported. Statistically significant anisotropy is
detected in all bands.Comment: 5 pages, 4 figures, uses emulateapj.sty, submitted to ApJ Letter
Microstructural strain energy of α-uranium determined by calorimetry and neutron diffractometry
The microstructural contribution to the heat capacity of α-uranium was determined by measuring the heat-capacity difference between polycrystalline and single-crystal samples from 77 to 320 K. When cooled to 77 K and then heated to about 280 K, the uranium microstructure released (3±1) J/mol of strain energy. On further heating to 300 K, the microstructure absorbed energy as it began to redevelop microstrains. Anisotropic strain-broadening parameters were extracted from neutron-diffraction measurements on polycrystals. Combining the strain-broadening parameters with anisotropic elastic constants from the literature, the microstructural strain energy is predicted in the two limiting cases of statistically isotropic stress and statistically isotropic strain. The result calculated in the limit of statistically isotropic stress was (3.7±0.5) J/mol K at 77 K and (1±0.5) J/mol at room temperature. In the limit of statistically isotropic strain, the values were (7.8±0.5) J/mol K at 77 K and (4.5±0.5) J/mol at room temperature. In both cases the changes in the microstructural strain energy showed good agreement with the calorimetry
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