42,748 research outputs found
Linearisation instability of gravity waves?
Gravity waves in irrotational dust spacetimes are characterised by nonzero
magnetic Weyl tensor . In the linearised theory, the divergence of
is set to zero. Recently Lesame et al. [Phys. Rev. D {\bf 53}, 738
(1996)] presented an argument to show that, in the exact nonlinear theory, forces , thus implying a linearisation instability for gravity
waves interacting with matter. However a sign error in the equations
invalidates their conclusion. Bianchi type V spacetimes are shown to include
examples with . An improved covariant formalism is used to
show that in a generic irrotational dust spacetime, the covariant constraint
equations are preserved under evolution. It is shown elsewhere that \mbox{div}
H=0 does not generate further conditions.Comment: 8 pages Revtex; to appear Phys. Rev.
Consistency of dust solutions with div H=0
One of the necessary covariant conditions for gravitational radiation is the
vanishing of the divergence of the magnetic Weyl tensor H_{ab}, while H_{ab}
itself is nonzero. We complete a recent analysis by showing that in
irrotational dust spacetimes, the condition div H=0 evolves consistently in the
exact nonlinear theory.Comment: 3 pages Revte
Direction Judgement Errors in Perspective Displays
Spatial information transfer characteristics of perspective situation displays were investigated by having eight subjects judge the directions of displayed targets relative to a fixed position in the center of computer generated perspective scenes. Their errors in judging azimuth angles varied sinusoidally with the azimuth of the targets. Errors alternated between clockwise and counterclock wise from one direction quadrant to the next. As the perspective geometry was varied between telephoto lens and wide angle lens views, the direction of error gradually reversed in all quadrants. The results can be explained by systematic differences between the three-dimensional stimulus angles and the perspective projections of those angles onto the display screen
MCFM for the Tevatron and the LHC
A summary is given of the current status of the next-to-leading order (NLO)
parton-level integrator MCFM. Some details are given about the Higgs + 2-jet
process and the production and decay of , both of which have
recently been added to the code. Using MCFM, comparisons between the Tevatron
running at ~TeV and the LHC running at ~TeV are made
for standard model process including the production of Higgs bosons. The case
for running the Tevatron until 16fb are accumulated by both detectors is
sketched.Comment: Talk presented by R.K Ellis at Loops and Legs in Quantum Field Theory
2010, Woerlitz, Germany, April 25-30, 2010, (6 pages and 4 figures
Supernova pencil beam survey
Type Ia supernovae (SNe Ia) can be calibrated to be good standard candles at
cosmological distances. We propose a supernova pencil beam survey that could
yield between dozens to hundreds of SNe Ia in redshift bins of 0.1 up to
, which would compliment space based SN searches, and enable the proper
consideration of the systematic uncertainties of SNe Ia as standard candles, in
particular, luminosity evolution and gravitational lensing. We simulate SNe Ia
luminosities by adding weak lensing noise (using empirical fitting formulae)
and scatter in SN Ia absolute magnitudes to standard candles placed at random
redshifts. We show that flux-averaging is powerful in reducing the combined
noise due to gravitational lensing and scatter in SN Ia absolute magnitudes.
The SN number count is not sensitive to matter distribution in the universe; it
can be used to test models of cosmology or to measure the SN rate. The SN
pencil beam survey can yield a wealth of data which should enable accurate
determination of the cosmological parameters and the SN rate, and provide
valuable information on the formation and evolution of galaxies.
The SN pencil beam survey can be accomplished on a dedicated 4 meter
telescope with a square degree field of view. This telescope can be used to
conduct other important observational projects compatible with the SN pencil
beam survey, such as QSOs, Kuiper belt objects, and in particular, weak lensing
measurements of field galaxies, and the search for gamma-ray burst afterglows.Comment: Final version, to appear in ApJ, 531, #2 (March 10, 2000). 22 pages
including 5 figures. Improved presentatio
QCD corrections to the hadronic production of a heavy quark pair and a W-boson including decay correlations
We perform an analytic calculation of the one-loop amplitude for the W-boson
mediated process 0 \to d u-bar Q Q-bar l-bar l, retaining the mass for the
quark Q. The momentum of each of the massive quarks is expressed as the sum of
two massless momenta and the corresponding heavy quark spinor is expressed as a
sum of two massless spinors. Using a special choice for the heavy quark spinors
we obtain analytic expressions for the one-loop amplitudes which are amenable
to fast numerical evaluation. The full next-to-leading order (NLO) calculation
of hadron+hadron \to W(\to e nu) b b-bar with massive b-quarks is included in
the program MCFM. A comparison is performed with previous published work.Comment: 45 pages, 17 figure
Hadronic production of a Higgs boson and two jets at next-to-leading order
We perform an update of the next-to-leading order calculation of the rate for
Higgs boson production in association with two jets. Our new calculation
incorporates the full analytic result for the one-loop virtual amplitude. This
new theoretical information allows us to construct a code including the decay
of the Higgs boson without incurring a prohibitive penalty in computer running
time. Results are presented for the Tevatron, where implications for the Higgs
search are sketched, and also for a range of scenarios at the LHC.Comment: 16 pages, 4 figure
Exact non-equilibrium solutions of the Einstein-Boltzmann equations. II
We find exact solutions of the Einstein-Boltzmann equations with relaxational
collision term in FRW and Bianchi I spacetimes. The kinematic and thermodynamic
properties of the solutions are investigated. We give an exact expression for
the bulk viscous pressure of an FRW distribution that relaxes towards
collision-dominated equilibrium. If the relaxation is toward collision-free
equilibrium, the bulk viscosity vanishes - but there is still entropy
production. The Bianchi I solutions have zero heat flux and bulk viscosity, but
nonzero shear viscosity. The solutions are used to construct a realisation of
the Weyl Curvature Hypothesis.Comment: 16 pages LaTex, CQG documentstyle (ioplppt
A Bait Attractant Study of the Nitidulidae (Coleoptera) at Shawnee State Forest in Southern Ohio
Four baits were tested for efficacy in attracting sap beetles (Nitidulidae) at two sites in the Shawnee State Forest over two collection periods in 1992. Species taken were categorized into three groups: abundant, moderate, and uncommon. At Site 1, nitidulids displayed a strong preference for whole wheat bread dough, followed by fermenting brown sugar, and fermenting malt/molasses solution, and vinegar, respectively. Site 2 collections showed a similar trend to Site 1, but the order of preference was switched for brown sugar and malt/molasses solution. Of the 20 species collected, six species were abundant, seven species were moderate, and seven species were locally uncommon
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