253 research outputs found
Is there an association between anti-TNF monoclonal antibody therapy in rheumatoid arthritis and risk of malignancy and serious infection? Commentary on the meta-analysis by Bongartz et al
A recent meta-analysis of randomized clinical trials reported by Bongartz and coworkers raised concerns about an increased rate of malignancy and serious infection in rheumatoid arthritis patients treated with anti-tumour necrosis factor monoclonal antibodies. This commentary discusses some of the methodological issues in their analysis and urges caution in interpreting the results
Testing Gravity in the Outer Solar System: Results from Trans-Neptunian Objects
The inverse square law of gravity is poorly probed by experimental tests at
distances of ~ 10 AUs. Recent analysis of the trajectory of the Pioneer 10 and
11 spacecraft have shown an unmodeled acceleration directed toward the Sun
which was not explained by any obvious spacecraft systematics, and occurred
when at distances greater than 20 AUs from the Sun. If this acceleration
represents a departure from Newtonian gravity or is indicative of an additional
mass distribution in the outer solar system, it should be detectable in the
orbits of Trans-Neptunian Objects (TNOs). To place limits on deviations from
Newtonian gravity, we have selected a well observed sample of TNOs found
orbiting between 20 and 100 AU from the Sun. By examining their orbits with
modified orbital fitting software, we place tight limits on the perturbations
of gravity that could exist in this region of the solar system.Comment: 20 pages, 4 figures, 2 tables, uses AASTex v5.x macro
Recommended from our members
Unresolved Questions in Rheumatology: Motion for Debate: The Data Support Evidence-Based Management Recommendations for Cardiovascular Disease in Rheumatoid Arthritis
Spinning Test Particle in Kalb-Ramond background
In this work we explore the geodesic deviations of spinning test particles in
a string inspired Einstein-Kalb Ramond background. Such a background is known
to be equivalent to a spacetime geometry with torsion. We have shown here that
the antisymmetric Kalb-Ramond field has significant effect on the geodesic
deviation of a spinning test particle. A search for an observational evidence
of such an effect in astrophysical experiments may lead to a better
undestanding of the geometry of the background spacetime.Comment: 14 pages, Latex, 5 figure
Challenges for Superstring Cosmology
We consider whether current notions about superstring theory below the Planck
scale are compatible with cosmology. We find that the anticipated form for the
dilaton interaction creates a serious roadblock for inflation and makes it
unlikely that the universe ever reaches a state with zero cosmological constant
and time-independent gravitational constant.Comment: 14 pages, 2 figures available as eps files on reques
Gravitational solution to the Pioneer 10/11 anomaly
A fully relativistic modified gravitational theory including a fifth force
skew symmetric field is fitted to the Pioneer 10/11 anomalous acceleration. The
theory allows for a variation with distance scales of the gravitational
constant G, the fifth force skew symmetric field coupling strength omega and
the mass of the skew symmetric field mu=1/lambda. A fit to the available
anomalous acceleration data for the Pioneer 10/11 spacecraft is obtained for a
phenomenological representation of the "running" constants and values of the
associated parameters are shown to exist that are consistent with fifth force
experimental bounds. The fit to the acceleration data is consistent with all
current satellite, laser ranging and observations for the inner planets.Comment: 14 pages, 3 figures, 3 tables. typo's were corrected at Equations (4)
and (12) and a third table including our predictions for the anomalous
perihelion advance of the planets was adde
Extended Inflation from Strings
We study the possibility of extended inflation in the effective theory of
gravity from strings compactified to four dimensions and find that it strongly
depends on the mechanism of supersymmetry breaking. We consider a general class
of string--inspired models which are good candidates for successful extended
inflation. In particular, the --problem of ordinary extended inflation
is automatically solved by the production of only very small bubbles until the
end of inflation. We find that the inflaton field could belong either to the
untwisted or to the twisted massless sectors of the string spectrum, depending
on the supersymmetry breaking superpotential.Comment: 18p
Canonical Formulation of Spin in General Relativity
The present thesis aims at an extension of the canonical formalism of
Arnowitt, Deser, and Misner from self-gravitating point-masses to objects with
spin. This would allow interesting applications, e.g., within the
post-Newtonian (PN) approximation. The extension succeeded via an action
approach to linear order in the single spins of the objects without restriction
to any further approximation. An order-by-order construction within the PN
approximation is possible and performed to the formal 3.5PN order as a
verification. In principle both approaches are applicable to higher orders in
spin. The PN next-to-leading order spin(1)-spin(1) level was tackled, modeling
the spin-induced quadrupole deformation by a single parameter. All
spin-dependent Hamiltonians for rapidly rotating bodies up to and including 3PN
are calculated.Comment: 59 pages. Dissertation, Friedrich-Schiller-Universit\"at, Jena, 2010.
This thesis was submitted in June 2010. Cite as Ann. Phys. (Berlin) 523:296
(2011
Non-precessional spin-orbit effects on gravitational waves from inspiraling compact binaries to second post-Newtonian order
We derive all second post-Newtonian (2PN), non-precessional effects of spin-
orbit coupling on the gravitational wave forms emitted by an inspiraling binary
composed of spinning, compact bodies in a quasicircular orbit. Previous post-
Newtonian calculations of spin-orbit effects (at 1.5PN order) relied on a fluid
description of the spinning bodies. We simplify the calculations by introducing
into post-Newtonian theory a delta-function description of the influence of the
spins on the bodies' energy-momentum tensor. This description was recently used
by Mino, Shibata, and Tanaka (MST) in Teukolsky-formalism analyses of particles
orbiting massive black holes, and is based on prior work by Dixon. We compute
the 2PN contributions to the wave forms by combining the MST energy-momentum
tensor with the formalism of Blanchet, Damour, and Iyer for evaluating the
binary's radiative multipoles, and with the well-known 1.5PN order equations of
motion for the binary. Our results contribute at 2PN order only to the
amplitudes of the wave forms. The secular evolution of the wave forms' phase,
the quantity most accurately measurable by LIGO, is not affected by our results
until 2.5PN order, at which point other spin-orbit effects also come into play.
We plan to evaluate the entire 2.5PN spin-orbit contribution to the secular
phase evolution in a future paper, using the techniques of this paper.Comment: 11 pages, submitted to Phys. Rev.
Gravitational ultrarelativistic spin-orbit interaction and the weak equivalence principle
It is shown that the gravitational ultrarelativistic spin-orbit interaction
violates the weak equivalence principle in the traditional sense. This fact is
a direct consequence of the Mathisson-Papapetrou equations in the frame of
reference comoving with a spinning test particle. The widely held assumption
that the deviation of a spinning test body from a geodesic trajectory is caused
by tidal forces is not correctComment: 12 page
- …