251 research outputs found
Is the physics within the Solar system really understood?
A collection is made of presently unexplained phenomena within our Solar
system and in the universe. These phenomena are (i) the Pioneer anomaly, (ii)
the flyby anomaly, (iii) the increase of the Astronomical Unit, (iv) the
quadrupole and octupole anomaly, and (v) Dark Energy and (vi) Dark Matter. A
new data analysis of the complete set of Pioneer data is announced in order to
search for systematic effects or to confirm the unexplained acceleration. We
also review the mysterious flyby anomaly where the velocities of spacecraft
after Earth swing--bys are larger than expected. We emphasize the scientific
aspects of this anomaly and propose systematic and continuous observations and
studies at the occasion of future flybys. Further anomalies within the Solar
system are the increase of the Astronomical Unit and the quadrupole and
octupole anomaly. We briefly mention Dark Matter and Dark Energy since in some
cases a relation between them and the Solar system anomalies have been
speculated.Comment: 22 pages, 3 figures, submitted for the proceedings of the 359th
WE-Heraeus Seminar on "Lasers, Clocks, and Drag-Free: Technologies for Future
Exploration in Space and Tests of Gravity
Summary of session C1: experimental gravitation
The fact that gravity is a metric theory follows from the Einstein equivalence principle. This principle consists of (i) the universality of free fall, (ii) the universality of the gravitational redshift and (iii) the local validity of Lorentz invariance. Many experiments searching for deviations from standard general relativity test the various aspects of the Einstein equivalence principle. Here we report on experiments covering the whole Einstein equivalence principle. Until now all experiments have been in agreement with the Einstein equivalence principle. As a consequence, gravity has to be described by a metric theory. Any metric theory of gravity leads to effects such as perihelion shift, deflection of light, gravitational redshift, gravitational time delay, LenseâThirring effect, Schiff effect, etc. A particular theory of that sort is Einstein's general relativity. For weak gravitational fields which are asymptotically flat any deviation from Einstein's general relativity can be parametrized by a few constants, the PPN parameters. Many astrophysical observations and space experiments are devoted to a better measurement of the effects and, thus, of the PPN parameters. It is clear that gravity is best tested for intermediate ranges, that is, for distances between 1 m and several astronomical units. It is highly interesting to push forward our domain of experience and to strengthen the experimental foundation of gravity also beyond these scales. This point is underlined by the fact that many quantum gravity and unification-inspired theories suggest deviation from the standard laws of gravity at very small or very large scales. In this session summary we briefly outline the status and report on the talks presented in session C1 about experimental gravitation
Analytic solutions of the geodesic equation in axially symmetric space-times
The complete sets of analytic solutions of the geodesic equation in
Taub--NUT--(anti-)de Sitter, Kerr--(anti-)de Sitter and also in general
Plebanski--Demianski space--times without acceleration are presented. The
solutions are given in terms of the Kleinian sigma functions.Comment: 4 pages, 4 figures, accepted for publication in EP
Lorentz invariance violation and charge (non--)conservation: A general theoretical frame for extensions of the Maxwell equations
All quantum gravity approaches lead to small modifications in the standard
laws of physics which lead to violations of Lorentz invariance. One particular
example is the extended standard model (SME). Here, a general phenomenological
approach for extensions of the Maxwell equations is presented which turns out
to be more general than the SME and which covers charge non--conservation
(CNC), too. The new Lorentz invariance violating terms cannot be probed by
optical experiments but need, instead, the exploration of the electromagnetic
field created by a point charge or a magnetic dipole. Some scalar--tensor
theories and higher dimensional brane theories predict CNC in four dimensions
and some models violating Special Relativity have been shown to be connected
with CNC and its relation to the Einstein Equivalence Principle has been
discussed. Due to this upcoming interest, the experimental status of electric
charge conservation is reviewed. Up to now there seem to exist no unique tests
of charge conservation. CNC is related to the precession of polarization, to a
modification of the --Coulomb potential, and to a time-dependence of the
fine structure constant. This gives the opportunity to describe a dedicated
search for CNC.Comment: To appear in Physical Review
Ideal-Modified Bosonic Gas Trapped in an Arbitrary Three Dimensional Power-Law Potential
We analyze the effects caused by an anomalous single-particle dispersion
relation suggested in several quantum-gravity models, upon the thermodynamics
of a Bose-Einstein condensate trapped in a generic 3-dimensional power-law
potential. We prove that the shift in the condensation temperature, caused by a
deformed dispersion relation, described as a non-trivial function of the number
of particles and the shape associated to the corresponding trap, could provide
bounds for the parameters associated to such deformation. Additionally, we
calculate the fluctuations in the number of particles as a criterium of
thermodynamic stability for these systems. We show that the apparent
instability caused by the anomalous fluctuations in the thermodynamic limit can
be suppressed considering the lowest energy associated to the system in
question.Comment: 10 pages. arXiv admin note: text overlap with arXiv:1202.380
Quantum nondemolition measurements of a particle in electric and gravitational fields
In this work we obtain a nondemolition variable for the case in which a
charged particle moves in the electric and gravitational fields of a spherical
body. Afterwards we consider the continuous monitoring of this nondemolition
parameter, and calculate along the ideas of the so called restricted path
integral formalism, the corresponding propagator. Using these results the
probabilities associated with the possible measurement outputs are evaluated.
The limit of our results, as the resolution of the measuring device goes to
zero, is analyzed, and the dependence of the corresponding propagator upon the
strength of the electric and gravitational fields are commented. The role that
mass plays in the corresponding results, and its possible connection with the
equivalence principle at quantum level, are studied.Comment: Accepted in International Journal of Modern Physics D, 14 page
Space--time fluctuations and the spreading of wavepackets
Using a density matrix description in space we study the evolution of
wavepackets in a fluctuating space-time background. We assume that space-time
fluctuations manifest as classical fluctuations of the metric. From the
non-relativistic limit of a non-minimally coupled Klein-Gordon equation we
derive a Schr\"odinger equation with an additive gaussian random potential.
This is transformed into an effective master equation for the density matrix.
The solutions of this master equation allow to study the dynamics of
wavepackets in a fluctuating space-time, depending on the fluctuation scenario.
We show how different scenarios alter the diffusion properties of wavepackets.Comment: 11 page
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