32 research outputs found
How current loops and solenoids curve space-time
The curved space-time around current loops and solenoids carrying arbitrarily
large steady electric currents is obtained from the numerical resolution of the
coupled Einstein-Maxwell equations in cylindrical symmetry. The artificial
gravitational field associated to the generation of a magnetic field produces
gravitational redshift of photons and deviation of light. Null geodesics in the
curved space-time of current loops and solenoids are also presented. We finally
propose an experimental setup, achievable with current technology of
superconducting coils, that produces a phase shift of light of the same order
of magnitude than astrophysical signals in ground-based gravitational wave
observatories.Comment: 12 pages, 8 figures, accepted for publication in PR
Interstellar travels aboard radiation-powered rockets
We model accelerated trips at high-velocity aboard light sails (beam-powered
propulsion in general) and radiation rockets (thrust by anisotropic emission of
radiation) in terms of Kinnersley's solution of general relativity and its
associated geodesics. The analysis of radiation rockets relativistic kinematics
shows that the true problem of interstellar travel is not really the amount of
propellant, nor the duration of the trip but rather its tremendous energy cost.
Indeed, a flyby of Proxima Centauri with an ultralight gram-scale laser sail
would require the energy produced by a 1 GW power plant during about one day,
while more than 15 times the current world energy production would be required
for sending a 100 tons radiation rocket to the nearest star system. The
deformation of the local celestial sphere aboard radiation rockets is obtained
through the null geodesics of Kinnersley's spacetime in the Hamiltonian
formulation. It is shown how relativistic aberration and Doppler effect for the
accelerated traveller differ from their description in special relativity for
motion at constant velocity. We also show how our results could interestingly
be extended to extremely luminous events like the large amount of gravitational
waves emitted by binary black hole mergers.Comment: 18 pages, 11 figures ; Open Acces
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
The Lemaitre-Schwarzschild Problem Revisited
The Lemaitre and Schwarzschild analytical solutions for a relativistic
spherical body of constant density are linked together through the use of the
Weyl quadratic invariant. The critical radius for gravitational collapse of an
incompressible fluid is shown to vary continuously from 9/8 of the
Schwarzschild radius to the Schwarzschild radius itself while the internal
pressures become locally anisotropic.Comment: Final version as accepted by GR&G (to appear in vol. 34, september
2002
The Abnormally Weighting Energy Hypothesis: the Missing Link between Dark Matter and Dark Energy
We generalize tensor-scalar theories of gravitation by the introduction of an
abnormally weighting type of energy. This theory of tensor-scalar anomalous
gravity is based on a relaxation of the weak equivalence principle that is now
restricted to ordinary visible matter only. As a consequence, the convergence
mechanism toward general relativity is modified and produces naturally cosmic
acceleration as an inescapable gravitational feedback induced by the
mass-variation of some invisible sector. The cosmological implications of this
new theoretical framework are studied. From the Hubble diagram cosmological
test \textit{alone}, this theory provides an estimation of the amount of
baryons and dark matter in the Universe that is consistent with the independent
cosmological tests of Cosmic Microwave Background (CMB) and Big Bang
Nucleosynthesis (BBN). Cosmic coincidence is naturally achieved from a equally
natural assumption on the amplitude of the scalar coupling strength. Finally,
from the adequacy to supernovae data, we derive a new intriguing relation
between the space-time dependences of the gravitational coupling and the dark
matter mass, providing an example of crucial constraint on microphysics from
cosmology. This glimpses at an enticing new symmetry between the visible and
invisible sectors, namely that the scalar charges of visible and invisible
matter are exactly opposite.Comment: 24 pages, 6 figures, new version with extended discussions and added
references. Accepted for publication in JCAP (sept. 2008
Statefinder diagnostic for cosmology with the abnormally weighting energy hypothesis
In this paper, we apply the statefinder diagnostic to the cosmology with the
Abnormally Weighting Energy hypothesis (AWE cosmology), in which dark energy in
the observational (ordinary matter) frame results from the violation of weak
equivalence principle (WEP) by pressureless matter. It is found that there
exist closed loops in the statefinder plane, which is an interesting
characteristic of the evolution trajectories of statefinder parameters and can
be used to distinguish AWE cosmology from the other cosmological models.Comment: 5 pages, 4 figures, accepted by PR
Thermodynamic analysis of black hole solutions in gravitating nonlinear electrodynamics
We perform a general study of the thermodynamic properties of static
electrically charged black hole solutions of nonlinear electrodynamics
minimally coupled to gravitation in three space dimensions. The Lagrangian
densities governing the dynamics of these models in flat space are defined as
arbitrary functions of the gauge field invariants, constrained by some
requirements for physical admissibility. The exhaustive classification of these
theories in flat space, in terms of the behaviour of the Lagrangian densities
in vacuum and on the boundary of their domain of definition, defines twelve
families of admissible models. When these models are coupled to gravity, the
flat space classification leads to a complete characterization of the
associated sets of gravitating electrostatic spherically symmetric solutions by
their central and asymptotic behaviours. We focus on nine of these families,
which support asymptotically Schwarzschild-like black hole configurations, for
which the thermodynamic analysis is possible and pertinent. In this way, the
thermodynamic laws are extended to the sets of black hole solutions of these
families, for which the generic behaviours of the relevant state variables are
classified and thoroughly analyzed in terms of the aforementioned boundary
properties of the Lagrangians. Moreover, we find universal scaling laws (which
hold and are the same for all the black hole solutions of models belonging to
any of the nine families) running the thermodynamic variables with the electric
charge and the horizon radius. These scale transformations form a one-parameter
multiplicative group, leading to universal "renormalization group"-like
first-order differential equations. The beams of characteristics of these
equations generate the full set of black hole states associated to any of these
gravitating nonlinear electrodynamics...Comment: 51 single column pages, 19 postscript figures, 2 tables, GRG tex
style; minor corrections added; final version appearing in General Relativity
and Gravitatio