307 research outputs found
Solving the BFKL Equation with Running Coupling
We describe a formalism for solving the BFKL equation with a coupling that
runs for momenta above a certain infrared cutoff. By suitably choosing matching
conditions proper account is taken of the fact that the BFKL diffusion implies
that the solution in the infrared (fixed coupling) regime depends upon the
solution in the ultraviolet (running coupling) regime and vice versa. Expanding
the BFKL kernel to a given order in the ratio of the transverse momenta allows
arbitrary accuracy to be achieved.Comment: 11 pages, 2 fig
Evaporation of a two-dimensional charged black hole
We construct a dilatonic two-dimensional model of a charged black hole. The
classical solution is a static charged black hole, characterized by two
parameters, and , representing the black hole's mass and charge. Then we
study the semiclassical effects, and calculate the evaporation rate of both
and , as a function of these two quantities. Analyzing this dynamical
system, we find two qualitatively different regimes, depending on the
electromagnetic coupling constant . If the latter is greater than a
certain critical value, the charge-to-mass ratio decays to zero upon
evaporation. On the other hand, for smaller than the critical value,
the charge-to-mass ratio approaches a non-zero constant that depends on
but not on the initial values of and .Comment: Latex, 30 pages, accepted for publication in Phys. Rev.
Viral Retinitis following Intraocular or Periocular Corticosteroid Administration: A Case Series and Comprehensive Review of the Literature.
Abstract Purpose: To describe viral retinitis following intravitreal and periocular corticosteroid administration. Methods: Retrospective case series and comprehensive literature review. Results: We analyzed 5 unreported and 25 previously published cases of viral retinitis following local corticosteroid administration. Causes of retinitis included 23 CMV (76.7%), 5 HSV (16.7%), and 1 each VZV and unspecified (3.3%). Two of 22 tested patients (9.1%) were HIV positive. Twenty-one of 30 (70.0%) cases followed one or more intravitreal injections of triamcinolone acetonide (TA), 4 (13.3%) after one or more posterior sub-Tenon injections of TA, 3 (10.0%) after placement of a 0.59-mg fluocinolone acetonide implant (Retisert), and 1 (3.3%) each after an anterior subconjunctival injection of TA (together with IVTA), an anterior chamber injection, and an anterior sub-Tenon injection. Mean time from most recent corticosteroid administration to development of retinitis was 4.2 months (median 3.8; range 0.25-13.0). Twelve patients (40.0%) had type II diabetes mellitus. Treatments used included systemic antiviral agents (26/30, 86.7%), intravitreal antiviral injections (20/30, 66.7%), and ganciclovir intravitreal implants (4/30, 13.3%). Conclusions: Viral retinitis may develop or reactivate following intraocular or periocular corticosteroid administration. Average time to development of retinitis was 4 months, and CMV was the most frequently observed agent. Diabetes was a frequent co-morbidity and several patients with uveitis who developed retinitis were also receiving systemic immunosuppressive therapy
The Strange Parton Distribution of the Nucleon: Global Analysis and Applications
The strangeness degrees of freedom in the parton structure of the nucleon are
explored in the global analysis framework, using the new CTEQ6.5 implementation
of the general mass perturbative QCD formalism of Collins. We systematically
determine the constraining power of available hard scattering experimental data
on the magnitude and shape of the strange quark and anti-quark parton
distributions. We find that current data favor a distinct shape of the strange
sea compared to the isoscalar non-strange sea. A new reference parton
distribution set, CTEQ6.5S0, and representative sets spanning the allowed
ranges of magnitude and shape of the strange distributions, are presented. Some
applications to physical processes of current interest in hadron collider
phenomenology are discussed.Comment: 19 pages; revised version submitted to JHE
Hawking Spectrum and High Frequency Dispersion
We study the spectrum of created particles in two-dimensional black hole
geometries for a linear, hermitian scalar field satisfying a Lorentz
non-invariant field equation with higher spatial derivative terms that are
suppressed by powers of a fundamental momentum scale . The preferred frame
is the ``free-fall frame" of the black hole. This model is a variation of
Unruh's sonic black hole analogy. We find that there are two qualitatively
different types of particle production in this model: a thermal Hawking flux
generated by ``mode conversion" at the black hole horizon, and a non-thermal
spectrum generated via scattering off the background into negative free-fall
frequency modes. This second process has nothing to do with black holes and
does not occur for the ordinary wave equation because such modes do not
propagate outside the horizon with positive Killing frequency. The horizon
component of the radiation is astonishingly close to a perfect thermal
spectrum: for the smoothest metric studied, with Hawking temperature
, agreement is of order at frequency
, and agreement to order persists out to
where the thermal number flux is ). The flux
from scattering dominates at large and becomes many orders of
magnitude larger than the horizon component for metrics with a ``kink", i.e. a
region of high curvature localized on a static worldline outside the horizon.
This non-thermal flux amounts to roughly 10\% of the total luminosity for the
kinkier metrics considered. The flux exhibits oscillations as a function of
frequency which can be explained by interference between the various
contributions to the flux.Comment: 32 pages, plain latex, 16 figures included using psfi
Wave Properties of Plasma Surrounding the Event Horizon of a Non-Rotating Black Hole
We have studied the wave properties of the cold and isothermal plasma in the
vicinity of the Schwarzschild black hole event horizon. The Fourier analyzed
perturbed 3+1 GRMHD equations are taken on the basis of which the complex
dispersion relations are obtained for non-rotating, rotating non-magnetized and
rotating magnetized backgrounds. The propagation and attenuation vectors along
with the refractive index are obtained (shown in graphs) to study the
dispersive properties of the medium near the event horizon. The results show
that no information can be obtained from the Schwarzschild magnetosphere.
Further, the pressure ceases the existence of normal dispersion of waves.Comment: 31 pages, 21 figures, accepted for publication in Canadian J. Phy
Plasma Wave Properties of the Schwarzschild Magnetosphere in a Veselago Medium
We re-formulate the 3+1 GRMHD equations for the Schwarzschild black hole in a
Veselago medium. Linear perturbation in rotating (non-magnetized and
magnetized) plasma is introduced and their Fourier analysis is considered. We
discuss wave properties with the help of wave vector, refractive index and
change in refractive index in the form of graphs. It is concluded that some
waves move away from the event horizon in this unusual medium. We conclude that
for the rotating non-magnetized plasma, our results confirm the presence of
Veselago medium while the rotating magnetized plasma does not provide any
evidence for this medium.Comment: 20 pages, 15 figures, accepted for publication in Astrophys. Space
Sc
Transverse Wave Propagation in Relativistic Two-fluid Plasmas in de Sitter Space
We investigate transverse electromagnetic waves propagating in a plasma in
the de Sitter space. Using the 3+1 formalism we derive the relativistic
two-fluid equations to take account of the effects due to the horizon and
describe the set of simultaneous linear equations for the perturbations. We use
a local approximation to investigate the one-dimensional radial propagation of
Alfv\'en and high frequency electromagnetic waves and solve the dispersion
relation for these waves numerically.Comment: 19 pages, 12 figure
Black Hole Evaporation in the Presence of a Short Distance Cutoff
A derivation of the Hawking effect is given which avoids reference to field
modes above some cutoff frequency in the free-fall frame
of the black hole. To avoid reference to arbitrarily high frequencies, it is
necessary to impose a boundary condition on the quantum field in a timelike
region near the horizon, rather than on a (spacelike) Cauchy surface either
outside the horizon or at early times before the horizon forms. Due to the
nature of the horizon as an infinite redshift surface, the correct boundary
condition at late times outside the horizon cannot be deduced, within the
confines of a theory that applies only below the cutoff, from initial
conditions prior to the formation of the hole. A boundary condition is
formulated which leads to the Hawking effect in a cutoff theory. It is argued
that it is possible the boundary condition is {\it not} satisfied, so that the
spectrum of black hole radiation may be significantly different from that
predicted by Hawking, even without the back-reaction near the horizon becoming
of order unity relative to the curvature.Comment: 35 pages, plain LaTeX, UMDGR93-32, NSF-ITP-93-2
A posteriori inclusion of parton density functions in NLO QCD final-state calculations at hadron colliders: The APPLGRID Project
A method to facilitate the consistent inclusion of cross-section measurements
based on complex final-states from HERA, TEVATRON and the LHC in proton parton
density function (PDF) fits has been developed. This can be used to increase
the sensitivity of LHC data to deviations from Standard Model predictions. The
method stores perturbative coefficients of NLO QCD calculations of final-state
observables measured in hadron colliders in look-up tables. This allows the
posteriori inclusion of parton density functions (PDFs), and of the strong
coupling, as well as the a posteriori variation of the renormalisation and
factorisation scales in cross-section calculations.
The main novelties in comparison to original work on the subject are the use
of higher-order interpolation, which substantially improves the trade-off
between accuracy and memory use, and a CPU and computer memory optimised way to
construct and store the look-up table using modern software tools.
It is demonstrated that a sufficient accuracy on the cross-section
calculation can be achieved with reasonably small look-up table size by using
the examples of jet production and electro-weak boson (Z, W) production in
proton-proton collisions at a center-of-mass energy of 14 TeV at the LHC.
The use of this technique in PDF fitting is demonstrated in a PDF-fit to HERA
data and simulated LHC jet cross-sections as well as in a study of the jet
cross-section uncertainties at various centre-of-mass energies
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