2,158 research outputs found
Quantum Gravity Momentum Representation and Maximum Invariant Energy
We use the idea of the symmetry between the spacetime coordinates x^\mu and
the energy-momentum p^\mu in quantum theory to construct a momentum space
quantum gravity geometry with a metric s_{\mu\nu} and a curvature
P^\lambda_{\mu\nu\rho}. For a closed maximally symmetric momentum space with a
constant 3-curvature, the volume of the p-space admits a cutoff with an
invariant maximum momentum a. A Wheeler-DeWitt-type wave equation is obtained
in the momentum space representation. The vacuum energy density and the
self-energy of a charged particle are shown to be finite, and modifications of
the electromagnetic radiation density and the entropy density of a system of
particles occur for high frequencies.Comment: 16 pages, LateX file, no figure
Noncommutative Einstein-AdS Gravity in three Dimensions
We present a Lorentzian version of three-dimensional noncommutative
Einstein-AdS gravity by making use of the Chern-Simons formulation of pure
gravity in 2+1 dimensions. The deformed action contains a real, symmetric
metric and a real, antisymmetric tensor that vanishes in the commutative limit.
These fields are coupled to two abelian gauge fields. We find that this theory
of gravity is invariant under a class of transformations that reduce to
standard diffeomorphisms once the noncommutativity parameter is set to zero.Comment: 11 pages, LaTeX, minor errors corrected, references adde
Low Gain Avalanche Detectors (LGAD) for particle physics and synchrotron applications
A new avalanche silicon detector concept is introduced with a low gain in the region of ten, known as a Low Gain Avalanche Detector, LGAD. The detector's characteristics are simulated via a full process simulation to obtain the required doping profiles which demonstrate the desired operational characteristics of high breakdown voltage (500 V) and a gain of 10 at 200 V reverse bias for X-ray detection. The first low gain avalanche detectors fabricated by Micron Semiconductor Ltd are presented. The doping profiles of the multiplication junctions were measured with SIMS and reproduced by simulating the full fabrication process which enabled further development of the manufacturing process. The detectors are 300 ÎŒm thick p-type silicon with a resistivity of 8.5 kΩcm, which fully depletes at 116 V. The current characteristics are presented and demonstrate breakdown voltages in excess of 500 V and a current density of 40 to 100 nAcmâ2 before breakdown measured at 20oC. The gain of the LGAD has been measured with a red laser (660 nm) and shown to be between 9 and 12 for an external bias voltage range from 150 V to 300 V
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
Time Delay Predictions in a Modified Gravity Theory
The time delay effect for planets and spacecraft is obtained from a fully
relativistic modified gravity theory including a fifth force skew symmetric
field by fitting to the Pioneer 10/11 anomalous acceleration data. A possible
detection of the predicted time delay corrections to general relativity for the
outer planets and future spacecraft missions is considered. The time delay
correction to GR predicted by the modified gravity is consistent with the
observational limit of the Doppler tracking measurement reported by the Cassini
spacecraft on its way to Saturn, and the correction increases to a value that
could be measured for a spacecraft approaching Neptune and Pluto.Comment: 5 pages, LaTex file, no figures. Corrections to Table
Wormholes in spacetime with torsion
Analytical wormhole solutions in theory are presented. It is discussed
whether the extremely short range repulsive forces, related to the spin angular
momentum of matter, could be the ``carrier'' of the exoticity that threads the
wormhole throat.Comment: 10 pages revte
The Dynamical Instability of Static, Spherically Symmetric Solutions in Nonsymmetric Gravitational Theories
We consider the dynamical stability of a class of static,
spherically-symmetric solutions of the nonsymmetric gravitational theory. We
numerically reproduce the Wyman solution and generate new solutions for the
case where the theory has a nontrivial fundamental length scale \mu^{-1}. By
considering spherically symmetric perturbations of these solutions we show that
the Wyman solutions are generically unstable.Comment: 13 pages, uses amslatex, graphicx and subfigure package
Experimental evidence of chaotic advection in a convective flow
Lagrangian chaos is experimentally investigated in a convective flow by means
of Particle Tracking Velocimetry. The Fnite Size Lyapunov Exponent analysis is
applied to quantify dispersion properties at different scales. In the range of
parameters of the experiment, Lagrangian motion is found to be chaotic.
Moreover, the Lyapunov depends on the Rayleigh number as . A
simple dimensional argument for explaining the observed power law scaling is
proposed.Comment: 7 pages, 3 figur
Gravitational memory of natural wormholes
A traversable wormhole solution of general scalar-tensor field equations is
presented. We have shown, after a numerical analysis for the behavior of the
scalar field of Brans-Dicke theory, that the solution is completely
singularity--free. Furthermore, the analysis of more general scalar field
dependent coupling constants indicates that the gravitational memory phenomenon
may play an important role in the fate of natural wormholes.Comment: 14 pages revtex, 1 ps figur
- âŠ