8,426 research outputs found
A Variable-Flavour Number Scheme for NNLO
At NNLO it is particularly important to have a Variable-Flavour Number Scheme
(VFNS) to deal with heavy quarks because there are major problems with both the
zero mass variable-flavour number scheme and the fixed-flavour number scheme. I
illustrate these problems and present a general formulation of a
Variable-Flavour Number Scheme (VFNS)for heavy quarks that is explicitly
implemented up to NNLO in the strong coupling constant alpha_S, and may be used
in NNLO global fits for parton distributions. The procedure combines elements
of the ACOT(chi) scheme and the Thorne-Roberts scheme. Despite the fact that at
NNLO the parton distributions are discontinuous as one changes the number of
active quark flavours, all physical quantities are continuous at flavour
transitions and the comparison with data is successful.Comment: 17 pages, 5 figures included as .ps files, uses axodraw. One
additional explanatory sentence after eq. (25). Correction of typos and
updated references. To be published in Phys. Rev.
Propagation of gravitational waves in multimetric gravity
We discuss the propagation of gravitational waves in a recently discussed
class of theories containing N >= 2 metric tensors and a corresponding number
of standard model copies. Using the formalism of gauge-invariant linear
perturbation theory we show that all gravitational waves propagate at the speed
of light. We then employ the Newman-Penrose formalism to show that two to six
polarizations of gravitational waves may exist, depending on the parameters
entering the equations of motion. This corresponds to E(2) representations N_2,
N_3, III_5 and II_6. We finally apply our general discussion to a recently
presented concrete multimetric gravity model and show that it is of class N_2,
i.e., it allows only two tensor polarizations, as it is the case for general
relativity. Our results provide the theoretical background for tests of
multimetric gravity theories using the upcoming gravitational wave experiments.Comment: 21 pages, no figures, journal versio
Complex Wave Numbers in the Vicinity of the Schwarzschild Event Horizon
This paper is devoted to investigate the cold plasma wave properties outside
the event horizon of the Schwarzschild planar analogue. The dispersion
relations are obtained from the corresponding Fourier analyzed equations for
non-rotating and rotating, non-magnetized and magnetized backgrounds. These
dispersion relations provide complex wave numbers. The wave numbers are shown
in graphs to discuss the nature and behavior of waves and the properties of
plasma lying in the vicinity of the Schwarzschild event horizon.Comment: 21 pages, 9 figures, accepted for publication Int. J. Mod. Phys.
Universal properties of the near-horizon optical geometry
We make use of the fact that the optical geometry near a static
non-degenerate Killing horizon is asymptotically hyperbolic to investigate
universal features of black hole physics. We show how the Gauss-Bonnet theorem
allows certain lensing scenarios to be ruled in or out. We find rates for the
loss of scalar, vector and fermionic `hair' as objects fall quasi- statically
towards the horizon. In the process we find the Lienard-Wiechert potential for
hyperbolic space and calculate the force between electrons mediated by
neutrinos, extending the flat space result of Feinberg and Sucher. We use the
enhanced conformal symmetry of the Schwarzschild and Reissner-Nordstrom
backgrounds to re-derive the electrostatic field due to a point charge in a
simple fashion
Locality in quantum gravity and string theory
Breakdown of local physics in string theory at distances longer than the
string scale is investigated. Such nonlocality would be expected to be visible
in ultrahigh-energy scattering. The results of various approaches to such
scattering are collected and examined. No evidence is found for non-locality
from strings whose length grows linearly with the energy. However, local
quantum field theory does apparently fail at scales determined by gravitational
physics, particularly strong gravitational dynamics. This amplifies locality
bound arguments that such failure of locality is a fundamental aspect of
physics. This kind of nonlocality could be a central element of a possible
loophole in the argument for information loss in black holes.Comment: 26 pages, 3 figures, harvmac. v2: minor changes to bring into accord
with revised paper hep-th/060519
Evolution of a Self-interacting Scalar Field in the spacetime of a Higher Dimensional Black Hole
In the spacetime of n-dimensional static charged black hole we examine the
mechanism by which the self-interacting scalar hair decay. It is turned out
that the intermediate asymptotic behaviour of the self-interacting scalar field
is determined by an oscilatory inverse power law. We confirm our results by
numerical calculations.Comment: RevTex, 6 pages, 8 figures, to be published in Phys.Rev.D1
Nonaxisymmetric instability of rapidly rotating black hole in five dimensions
We present results from numerical solution of Einstein's equation in five
dimensions describing evolution of rapidly rotating black holes. We show, for
the first time, that the rapidly rotating black holes in higher dimensions are
unstable against nonaxisymmetric deformation; for the five-dimensional case,
the critical value of spin parameter for onset of the instability is .Comment: 4 pages, 3 figures, accepted for publication in PRD(R
Relativistic Radiative Transfer for Spherical Flows
We present a new complete set of Lagrangian relativistic hydrodynamical
equations describing the transfer of energy and momentum between a standard
fluid and a radiation fluid in a general non-stationary spherical flow. The new
set of equations has been derived for a particular application to the study of
the cosmological Quark--Hadron transition but can also be used in other
contexts.Comment: 28 pages, 9 postscript figs, Plain Te
LISA detections of massive black hole inspirals: parameter extraction errors due to inaccurate template waveforms
The planned Laser Interferometer Space Antenna (LISA) is expected to detect
the inspiral and merger of massive black hole binaries (MBHBs) at z <~ 5 with
signal-to-noise ratios (SNRs) of hundreds to thousands. Because of these high
SNRs, and because these SNRs accrete over periods of weeks to months, it should
be possible to extract the physical parameters of these systems with high
accuracy; for instance, for a ~ 10^6 Msun MBHBs at z = 1 it should be possible
to determine the two masses to ~ 0.1% and the sky location to ~ 1 degree.
However, those are just the errors due to noise: there will be additional
"theoretical" errors due to inaccuracies in our best model waveforms, which are
still only approximate. The goal of this paper is to estimate the typical
magnitude of these theoretical errors. We develop mathematical tools for this
purpose, and apply them to a somewhat simplified version of the MBHB problem,
in which we consider just the inspiral part of the waveform and neglect
spin-induced precession, eccentricity, and PN amplitude corrections. For this
simplified version, we estimate that theoretical uncertainties in sky position
will typically be ~ 1 degree, i.e., comparable to the statistical uncertainty.
For the mass and spin parameters, our results suggest that while theoretical
errors will be rather small absolutely, they could still dominate over
statistical errors (by roughly an order of magnitude) for the strongest
sources. The tools developed here should be useful for estimating the magnitude
of theoretical errors in many other problems in gravitational-wave astronomy.Comment: RevTeX4, 16 pages, 2 EPS figures. Corrected typos, clarified
statement
Defining the Costs of an Outbreak of Karnal Bunt of Wheat
In determining the economic impact of a possible outbreak of the quarantinable wheat disease Karnal Bunt, an examination was made of the detailed components of the costs involved. The costs were classified as: (a) Direct costs (yield and quality losses); (b) Reaction costs (export bans, quality down-grading, seed industry costs); and (c) Control costs (quarantine zones, fungicides, spore destruction). The relative importance of each of these cost components is measured for a hypothetical outbreak of Karnal Bunt in the European Union, as a means of ensuring that the policy responses to such an outbreak are appropriate considering the costs involved.disease, quarantine, cost, wheat, Agricultural and Food Policy, Crop Production/Industries,
- …