94 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
The Jungle Universe
In this paper, we exploit the fact that the dynamics of homogeneous and
isotropic Friedmann-Lemaitre universes is a special case of generalized
Lotka-Volterra system where the competitive species are the barotropic fluids
filling the Universe. Without coupling between those fluids, Lotka-Volterra
formulation offers a pedagogical and simple way to interpret usual
Friedmann-Lemaitre cosmological dynamics. A natural and physical coupling
between cosmological fluids is proposed which preserve the structure of the
dynamical equations. Using the standard tools of Lotka-Volterra dynamics, we
obtain the general Lyapunov function of the system when one of the fluids is
coupled to dark energy. This provides in a rigorous form a generic asymptotic
behavior for cosmic expansion in presence of coupled species, beyond the
standard de Sitter, Einstein-de Sitter and Milne cosmologies. Finally, we
conjecture that chaos can appear for at least four interacting fluids.Comment: 26 pages, 4 figure
Fab Four: When John and George play gravitation and cosmology
Scalar-tensor theories of gravitation have recently regained a great interest
after the discovery of the Chameleon mechanism and of the Galileon models. The
former allows, in principle, to reconcile the presence of cosmological scalar
fields with the constraints from experiments at the Solar System scale. The
latter open up the possibility of building inflationary models that, among
other things, do not need ad hoc potentials. Further generalizations have
finally led to the most general tensor-scalar theory, recently dubbed the "Fab
Four", with only first and second order derivatives of the fields in the
equations of motion and that self-tune to a vanishing cosmological constant.
This model has a very rich phenomenology that needs to be explored and
confronted with experimental data in order to constrain a very large parameter
space. In this paper, we present some results regarding a subset of the theory
named "John", which corresponds to a non-minimal derivative coupling between
the scalar field and the Einstein tensor in the action. We show that this
coupling gives rise to an inflationary model with very unnatural initial
conditions. Thus, we include a non-minimal, but non-derivative, coupling
between scalar field and Ricci scalar, a term named "George" in the Fab Four
terminology. In this way, we find a more sensible inflationary model, and, by
performing a post-newtonian expansion of spherically symmetric solutions, we
derive the set of equations that constrain the parameter space with data from
experiments in the solar system.Comment: Minor changes, references added. Version accepted for publication in
Advances in Astronom
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
Generalized gauge field theories with non-topological soliton solutions
We perform a systematic analysis of the conditions under which
\textit{generalized} gauge field theories of compact semisimple Lie groups
exhibit electrostatic spherically symmetric non-topological soliton solutions
in three space dimensions. By the term \textit{generalized}, we mean that the
dynamics of the concerned fields is governed by lagrangian densities which are
general functions of the quadratic field invariants, leading to physically
consistent models. The analysis defines exhaustively the class of this kind of
lagrangian models supporting those soliton solutions and leads to methods for
their explicit determination. The necessary and sufficient conditions for the
linear stability of the finite-energy solutions against charge-preserving
perturbations are established, going beyond the usual Derrick-like criteria,
which only provides necessary conditions.Comment: 6 pages, revtex
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