14,670 research outputs found
Satellite measurement of the Hannay angle
The concept of a measurement of the yet unevaluated Hannay angle, by means of
an Earth-bound satellite, adiabatically driven by the Moon, is shown herein.
Numerical estimates are given for the angles, the orbital displacements, the
shortening of the orbital periods, for different altitudes. It is concluded
that the Hannay effect is measurable in high Earth orbits, by means of atomic
clocks, accurate Time & Frequency transfer system and precise positioning.Comment: Lette
Solar wind test of the de Broglie-Proca's massive photon with Cluster multi-spacecraft data
Our understanding of the universe at large and small scales relies largely on
electromagnetic observations. As photons are the messengers, fundamental
physics has a concern in testing their properties, including the absence of
mass. We use Cluster four spacecraft data in the solar wind at 1 AU to estimate
the mass upper limit for the photon. We look for deviations from Amp\`ere's
law, through the curlometer technique for the computation of the magnetic
field, and through the measurements of ion and electron velocities for the
computation of the current. We show that the upper bound for lies
between and kg, and thereby discuss
the currently accepted lower limits in the solar wind.Comment: The paper points out that actual photon mass upper limits (in the
solar wind) are too optimistic and model based. We instead perform a much
more experiment oriented measurement. This version matches that accepted by
Astroparticle Physic
A source-free integration method for black hole perturbations and self-force computation: Radial fall
Perturbations of Schwarzschild-Droste black holes in the Regge-Wheeler gauge
benefit from the availability of a wave equation and from the gauge invariance
of the wave function, but lack smoothness. Nevertheless, the even perturbations
belong to the C\textsuperscript{0} continuity class, if the wave function and
its derivatives satisfy specific conditions on the discontinuities, known as
jump conditions, at the particle position. These conditions suggest a new way
for dealing with finite element integration in time domain. The forward time
value in the upper node of the ) grid cell is obtained by the linear
combination of the three preceding node values and of analytic expressions
based on the jump conditions. The numerical integration does not deal directly
with the source term, the associated singularities and the potential. This
amounts to an indirect integration of the wave equation. The known wave forms
at infinity are recovered and the wave function at the particle position is
shown. In this series of papers, the radial trajectory is dealt with first,
being this method of integration applicable to generic orbits of EMRI (Extreme
Mass Ratio Inspiral).Comment: This arXiv version differs from the one to be published by Phys. Rev.
D for the use of British English and other minor editorial difference
Feedback stabilization of dynamical systems with switched delays
We analyze a classification of two main families of controllers that are of
interest when the feedback loop is subject to switching propagation delays due
to routing via a wireless multi-hop communication network. We show that we can
cast this problem as a subclass of classical switching systems, which is a
non-trivial generalization of classical LTI systems with timevarying delays. We
consider both cases where delay-dependent and delay independent controllers are
used, and show that both can be modeled as switching systems with unconstrained
switchings. We provide NP-hardness results for the stability verification
problem, and propose a general methodology for approximate stability analysis
with arbitrary precision. We finally give evidence that non-trivial design
problems arise for which new algorithmic methods are needed
Gauge dependence and self-force from Galilean to Einsteinian free fall, compact stars falling into black holes, Hawking radiation and the Pisa tower at the general relativity centennial
(Short abstract). In Galilean physics, the universality of free fall implies
an inertial frame, which in turns implies that the mass m of the falling body
is omitted. Otherwise, an additional acceleration proportional to m/M would
rise either for an observer at the centre of mass of the system, or for an
observer at a fixed distance from the centre of mass of M. These elementary,
but overlooked, considerations fully respect the equivalence principle and the
identity of an inertial or a gravitational pull for an observer in the Einstein
cabin. They value as fore-runners of the self-force and gauge dependency in
general relativity. The approximate nature of Galilei's law of free fall is
explored herein. When stepping into general relativity, we report how the
geodesic free fall into a black hole was the subject of an intense debate again
centred on coordinate choice. Later, we describe how the infalling mass and the
emitted gravitational radiation affect the free fall motion of a body. The
general relativistic self-force might be dealt with to perfectly fit into a
geodesic conception of motion. Then, embracing quantum mechanics, real black
holes are not classical static objects any longer. Free fall has to handle the
Hawking radiation, and leads us to new perspectives on the varying mass of the
evaporating black hole and on the varying energy of the falling mass. Along the
paper, we also estimate our findings for ordinary masses being dropped from a
Galilean or Einsteinian Pisa-like tower with respect to the current state of
the art drawn from precise measurements in ground and space laboratories, and
to the constraints posed by quantum measurements. The appendix describes how
education physics and high impact factor journals discuss the free fall.
Finally, case studies conducted on undergraduate students and teachers are
reviewed
Has the Quark-Gluon Plasma been seen?
Data from the first three years of running at RHIC are reviewed and put into
context with data obtained previously at the AGS and SPS and with the physics
question of creation of a quark-gluon plasma in high energy heavy ion
collisions. Also some very recent and still preliminary data from run4 are
included.Comment: plenary paper, Lepton-Photon 2005, Uppsala, Swede
Planck-scale modifications to Electrodynamics characterized by a space-like symmetry-breaking vector
In the study of Planck-scale ("quantum-gravity induced") violations of
Lorentz symmetry, an important role was played by the deformed-electrodynamics
model introduced by Myers and Pospelov. Its reliance on conventional effective
quantum field theory, and its description of symmetry-violation effects simply
in terms of a four-vector with nonzero component only in the time-direction,
rendered it an ideal target for experimentalists and a natural concept-testing
ground for many theorists. At this point however the experimental limits on the
single Myers-Pospelov parameter, after improving steadily over these past few
years, are "super-Planckian", {\it i.e.} they take the model out of actual
interest from a conventional quantum-gravity perspective. In light of this we
here argue that it may be appropriate to move on to the next level of
complexity, still with vectorial symmetry violation but adopting a generic
four-vector. We also offer a preliminary characterization of the phenomenology
of this more general framework, sufficient to expose a rather significant
increase in complexity with respect to the original Myers-Pospelov setup. Most
of these novel features are linked to the presence of spatial anisotropy, which
is particularly pronounced when the symmetry-breaking vector is space-like, and
they are such that they reduce the bound-setting power of certain types of
observations in astrophysics
Entropy theorems in classical mechanics, general relativity, and the gravitational two-body problem
In classical Hamiltonian theories, entropy may be understood either as a
statistical property of canonical systems, or as a mechanical property, that
is, as a monotonic function of the phase space along trajectories. In classical
mechanics, there are theorems which have been proposed for proving the
non-existence of entropy in the latter sense. We explicate, clarify and extend
the proofs of these theorems to some standard matter (scalar and
electromagnetic) field theories in curved spacetime, and then we show why these
proofs fail in general relativity; due to properties of the gravitational
Hamiltonian and phase space measures, the second law of thermodynamics holds.
As a concrete application, we focus on the consequences of these results for
the gravitational two-body problem, and in particular, we prove the
non-compactness of the phase space of perturbed Schwarzschild-Droste
spacetimes. We thus identify the lack of recurring orbits in phase space as a
distinct sign of dissipation and hence entropy production.Comment: 39 pages, 3 figures; v2: version to appear in Phys. Rev. D,
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