1,093 research outputs found
Lunar science from lunar laser ranging
Seventeen years of lunar ranging data have been analyzed to determine lunar second-degree moment differences, third-degree gravitational harmonics, Love number, rotational dissipation and retroreflector coordinates
Dark Energy as a Born-Infeld Gauge Interaction Violating the Equivalence Principle
We investigate the possibility that dark energy does not couple to
gravitation in the same way than ordinary matter, yielding a violation of the
weak and strong equivalence principles on cosmological scales. We build a
transient mechanism in which gravitation is pushed away from general relativity
by a Born-Infeld gauge interaction acting as an "Abnormally Weighting" (dark)
Energy. This mechanism accounts for the Hubble diagram of far-away supernovae
by cosmic acceleration and time variation of the gravitational constant while
accounting naturally for the present tests on general relativity.Comment: 5 pages, 3 figures, sequel of Phys. Rev. D 73 023520 (2006), to
appear in Physical Review Letter
Baryogenesis after Hyperextended Inflation
We study a baryogenesis mechanism operating in the context of hyperextended
inflation and making use of a coupling between the scalar field and a standard
model global current, such as B or B-L. The method is efficient at temperatures
at which these currents are not conserved due to some higher dimensional
operator. The particle physics and cosmological phenomenology are discussed. We
consider constraints stemming from nucleosynthesis and solar system
experiments.Comment: 7 pages, 1 figure, uses RevTe
A Note on Frame Dragging
The measurement of spin effects in general relativity has recently taken
centre stage with the successfully launched Gravity Probe B experiment coming
toward an end, coupled with recently reported measurements using laser ranging.
Many accounts of these experiments have been in terms of frame-dragging. We
point out that this terminology has given rise to much confusion and that a
better description is in terms of spin-orbit and spin-spin effects. In
particular, we point out that the de Sitter precession (which has been mesured
to a high accuracy) is also a frame-dragging effect and provides an accurate
benchmark measurement of spin-orbit effects which GPB needs to emulate
Gravitational Acceleration of Spinning Bodies From Lunar Laser Ranging Measurements
The Sun's relativistic gravitational gradient accelerations of Earth and
Moon, dependent on the motions of the latter bodies, act upon the system's
internal angular momentum. This spin-orbit force (which plays a part in
determining the gravity wave signal templates for astrophysical sources)
slightly accelerates the Earth-Moon system as a whole, but it more robustly
perturbs that system's internal dynamics with a 5 cm, synodically oscillating
range contribution which is presently measured to 4 mm precision by more than
three decades of lunar laser ranging.Comment: 10 pages, PCTex32.v3.
Quintessence Models and the Cosmological Evolution of alpha
The cosmological evolution of a quintessence-like scalar field, phi, coupled
to matter and gauge fields leads to effective modifications of the coupling
constants and particle masses over time. We analyze a class of models where the
scalar field potential V(phi) and the couplings to matter B(phi) admit common
extremum in phi, as in the Damour-Polyakov ansatz. We find that even for the
simplest choices of potentials and B(phi), the observational constraints on
delta alpha/alpha coming from quasar absorption spectra, the Oklo phenomenon
and Big Bang nucleosynthesis provide complementary constraints on the
parameters of the model. We show the evolutionary history of these models in
some detail and describe the effects of a varying mass for dark matter.Comment: 26 pages, 20 eps figure
Magnetism of PdNi alloys near the critical concentration for ferromagnetism
We report results of a muon spin rotation and relaxation (SR) study of
dilute PdNi alloys, with emphasis on Ni concentrations 0.0243
and 0.025. These are close to the critical value for the onset
of ferromagnetic long-range order (LRO), which is a candidate for a quantum
critical point. The 2.43 and 2.5 at.% Ni alloys exhibit similar SR
properties. Both samples are fully magnetic, with average muon local fields
2.0 and 3.8 mT and Curie temperatures
1.0 and 2.03 K for 2.43 and 2.5 at.% Ni, respectively, at . The
temperature dependence of suggests ordering of
Ni spin clusters rather than isolated spins. Just above a two-phase
region is found with separate volume fractions of quasistatic short-range order
(SRO) and paramagnetism. The SRO fraction decreases to zero with increasing
temperature a few kelvin above . This mixture of SRO and paramagnetism is
consistent with the notion of an inhomogeneous alloy with Ni clustering. The
measured values of extrapolate to = 0.0236 0.0027.
The dynamic muon spin relaxation in the vicinity of differs for the two
samples: a relaxation-rate maximum at is observed for = 0.0243,
reminiscent of critical slowing down, whereas for 0.025 no dynamic
relaxation is observed within the SR time window. The data suggest a
mean-field-like transition in this alloy.Comment: 15 pages, 15 figures, to be published in Phys. Rev.
Free Boundary Poisson Bracket Algebra in Ashtekar's Formalism
We consider the algebra of spatial diffeomorphisms and gauge transformations
in the canonical formalism of General Relativity in the Ashtekar and ADM
variables. Modifying the Poisson bracket by including surface terms in
accordance with our previous proposal allows us to consider all local
functionals as differentiable. We show that closure of the algebra under
consideration can be achieved by choosing surface terms in the expressions for
the generators prior to imposing any boundary conditions. An essential point is
that the Poisson structure in the Ashtekar formalism differs from the canonical
one by boundary terms.Comment: 19 pages, Latex, amsfonts.sty, amssymb.st
Progress in Lunar Laser Ranging Tests of Relativistic Gravity
Analyses of laser ranges to the Moon provide increasingly stringent limits on
any violation of the Equivalence Principle (EP); they also enable several very
accurate tests of relativistic gravity. We report the results of our recent
analysis of Lunar Laser Ranging (LLR) data giving an EP test of \Delta
(M_G/M_I)_{EP} =(-1.0 +/- 1.4) x 10^{-13}. This result yields a Strong
Equivalence Principle (SEP) test of \Delta (M_G/M_I)_{SEP} =(-2.0 +/- 2.0) x
10^{-13}. Also, the corresponding SEP violation parameter \eta is (4.4 +/- 4.5)
x 10^{-4}, where \eta=4\beta-\gamma-3 and both \beta and \gamma are
parametrized post-Newtonian (PPN) parameters. Using the recent Cassini result
for the parameter \gamma, PPN parameter \beta is determined to be \beta-1=(1.2
+/- 1.1) x 10^{-4}. The geodetic precession test, expressed as a relative
deviation from general relativity, is K_{gp}=-0.0019 +/- 0.0064. The search for
a time variation in the gravitational constant results in \dot G/G=(4 +/- 9) x
10^{-13} yr^{-1}, consequently there is no evidence for local (~1AU) scale
expansion of the solar system.Comment: 4 pages, revtex4, minor changes made for publicatio
On the water-bag model of dispersionless KP hierarchy
We investigate the bi-Hamiltonian structure of the waterbag model of dKP for
two component case. One can establish the third-order and first-order
Hamiltonian operator associated with the waterbag model. Also, the dispersive
corrections are discussed.Comment: 19 page
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