36,900 research outputs found
Early thermalization at RHIC
It is shown that recent RHIC data on hadron spectra and elliptic flow can be
excellently reproduced within a hydrodynamic description of the collision
dynamics, and that this provides strong evidence for rapid thermalization while
the system is still in the quark-gluon plasma phase. But even though the
hydrodynamic approach provides an impressive description of the single-particle
momentum distributions, it fails to describe the two-particle momentum
correlation (HBT) data for central Au+Au collisions at RHIC. We suggest that
this is not likely to be repaired by further improvements in our understanding
of the early collision stages, but probably requires a better modelling of the
freeze-out process. We close with a prediction of the phases of the azimuthal
oscillations of the HBT radii in noncentral collisions at RHIC.Comment: 12 pages, including 6 figures. Invited talk at the International
Conference on "Statistical QCD", Bielefeld, August 26-30, 2001, to appear in
the proceedings (F. Karsch and H. Satz, eds.) in Nucl. Phys.
Tail asymptotics for the maximum of perturbed random walk
Consider a random walk that is ``perturbed'' by a
stationary sequence to produce the process
. This paper is concerned with computing the distribution
of the all-time maximum of perturbed
random walk with a negative drift. Such a maximum arises in several different
applications settings, including production systems, communications networks
and insurance risk. Our main results describe asymptotics for
as . The tail asymptotics depend greatly
on whether the 's are light-tailed or heavy-tailed. In the light-tailed
setting, the tail asymptotic is closely related to the Cram\'{e}r--Lundberg
asymptotic for standard random walk.Comment: Published at http://dx.doi.org/10.1214/105051606000000268 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Selling Solar: Financing Household Solar Energy in the Developing World
Based on value chain analyses of case studies, outlines the issues and challenges for developing a solar energy industry, with a focus on the need for a financing infrastructure that serves purchasers, manufacturers, distributors, and investors
Thermal history of the early Miocene Waitemata Basin and adjacent Waipapa Group, North Island, New Zealand
Apatite fission track (AFT) and vitrinite reflectance (VR) data for early Miocene outcrops from the Waitemata Basin reveal that the basin sequence was subjected to shallow burial before denudation. AFT results suggest that the total sediment thickness within the basin was <=1 km and maximum paleotemperatures during burial never exceeded c. 60deg.C. Statistical analyses of the detrital AFT ages distinguish four dominant sources of sediment supply: contemporaneous volcanism; metagreywacke rocks of the Waipapa Group; the Northland Allochthon; and an unidentified source south of the basin.
The apatite and zircon fission track results from the Waipapa Group rocks (Gondwana Terrane) adjacent to the basin suggest two discrete phases of accelerated cooling: the first during the early Cretaceous (c. 117 Ma) and the second during the mid Cretaceous (c. 84 Ma). These events probably reflect key stages in the tectonic development of the New Zealand microcontinent during the Cretaceous period, the earlier event being related to the climax of compressional deformation (Rangitata Orogeny) and the latter to extensional tectonism associated with the opening of the Tasman Sea. Waipapa Group rocks now exposed at the surface cooled from maximum paleotemperatures of c. 250deg.C at an estimated rate of c. 180-36deg.C/m.y., involving substantial denudation
Indirect Signals from Dark Matter in Split Supersymmetry
We study the possibilities for the indirect detection of dark matter in Split
Supersymmetry from gamma-rays, positrons, and antiprotons. The most promising
signal is the gamma-ray line, which may be observable at the next generation of
detectors. For certain halo profiles and a high mass neutralino, the line can
even be visible in current experiments. The continuous gamma-ray signal may be
observable, if there is a central spike in the galactic halo density. The
signals are found to be similar to those in MSSM models. These indirect signals
complement other experiments, being most easily observable for regions of
parameter space, such as heavy wino and higgsino dominated neutralinos, which
are least accessible for direct detection and accelerator searches.Comment: 10 pages, 5 figures; experimental sensitivities added to figure 2,
revised version to appear in Phys. Rev.
An electric-field representation of the harmonic XY model
The two-dimensional harmonic XY (HXY) model is a spin model in which the
classical spins interact via a piecewise parabolic potential. We argue that the
HXY model should be regarded as the canonical classical lattice spin model of
phase fluctuations in two-dimensional condensates, as it is the simplest model
that guarantees the modular symmetry of the experimental systems. Here we
formulate a lattice electric-field representation of the HXY model and contrast
this with an analogous representation of the Villain model and the
two-dimensional Coulomb gas with a purely rotational auxiliary field. We find
that the HXY model is a spin-model analogue of a lattice electric-field model
of the Coulomb gas with an auxiliary field, but with a temperature-dependent
vacuum (electric) permittivity that encodes the coupling of the spin vortices
to their background spin-wave medium. The spin vortices map to the Coulomb
charges, while the spin-wave fluctuations correspond to auxiliary-field
fluctuations. The coupling explains the striking differences in the
high-temperature asymptotes of the specific heats of the HXY model and the
Coulomb gas with an auxiliary field. Our results elucidate the propagation of
effective long-range interactions throughout the HXY model (whose interactions
are purely local) by the lattice electric fields. They also imply that global
spin-twist excitations (topological-sector fluctuations) generated by local
spin dynamics are ergodically excluded in the low-temperature phase. We discuss
the relevance of these results to condensate physics.Comment: 13 pages, 10 figure
Topological-sector fluctuations and ergodicity breaking at the Berezinskii-Kosterlitz-Thouless transition
The Berezinskii-Kosterlitz-Thouless (BKT) phase transition drives the
unbinding of topological defects in many two-dimensional systems. In the
two-dimensional Coulomb gas, it corresponds to an insulator-conductor
transition driven by charge deconfinement. We investigate the global
topological properties of this transition, both analytically and by numerical
simulation, using a lattice-field description of the two-dimensional Coulomb
gas on a torus. The BKT transition is shown to be an ergodicity breaking
between the topological sectors of the electric field, which implies a
definition of topological order in terms of broken ergodicity. The breakdown of
local topological order at the BKT transition leads to the excitation of global
topological defects in the electric field, corresponding to different
topological sectors. The quantized nature of these classical excitations, and
their strict suppression by ergodicity breaking in the low-temperature phase,
afford striking global signatures of topological-sector fluctuations at the BKT
transition. We discuss how these signatures could be detected in experiments
on, for example, magnetic films and cold-atom systems.Comment: 11 pages, 6 figure
Chiral Rings, Vacua and Gaugino Condensation of Supersymmetric Gauge Theories
We find the complete chiral ring relations of the supersymmetric U(N) gauge
theories with matter in adjoint representation. We demonstrate exact
correspondence between the solutions of the chiral ring and the supersymmetric
vacua of the gauge theory. The chiral ring determines the expectation values of
chiral operators and the low energy gauge group. All the vacua have nonzero
gaugino condensation. We study the chiral ring relations obeyed by the gaugino
condensate. These relations are generalizations of the formula
of the pure gauge theory.Comment: 38 page
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