arXiv subjects

Serge Reynaud

Publications and source records attributed to Serge Reynaud.

At least 73 records · Page 4Linked to original sources

arXiv2011

Tests of gravity at the solar system scale

As confirmed by tests performed in the solar system, General Relativity (GR) presently represents the best description of gravitation. It is however challenged by observations at very large length scales, and already at the solar system scale, tracking of the Pioneer 10/11 probes has failed to confirm their expected behavior according to GR. Metric extensions of GR, which are presented here, have the quality of preserving the fundamental properties of GR while introducing scale dependent modifications. We show that they moreover represent an appropriate family of gravitation theories to be compared with observations when analysing gravity tests. We also discuss different tests which could allow one to determine the metric extension of GR prevailing in the solar system.

gr-qc↗

arXiv2011

Odyssey 2 : A mission toward Neptune and Triton to test General Relativity

Odyssey 2 will be proposed in December 2010 for the next call of M3 missions for Cosmic Vision 2015-2025. This mission, under a Phase 0 study performed by CNES, will aim at Neptune and Triton. Two sets of objectives will be pursued. The first one is to perform a set of gravitation experiments at the Solar System scale. Experimental tests of gravitation have always shown good agreement with General Relativity. There are however drivers to continue testing General Relativity, and to do so at the largest possible scales. From a theoretical point of view, Einstein's theory of gravitation shows inconsistencies with a quantum description of Nature and unified theories predict deviations from General Relativity. From an observational point of view, as long as dark matter and dark energy are not observed through other means than their gravitational effects, they can be considered as a manifestation of a modification of General Relativity at cosmic scales. The scientific objectives are to: (i) test the gravitation law at the Solar System scale; (ii) measure the Eddington parameter; and (iii) investigate the navigation anomalies during fly-bys. To fulfil these objectives, the following components are to be on board the spacecraft: (i) the Gravity Advanced Package (GAP), which is an electrostatic accelerometer to which a rotating stage is added; (ii) radio-science; (iii) laser ranging, to improve significantly the measure of the Eddington parameter. The second set of objectives is to enhance our knowledge of Neptune and Triton. Several instruments dedicated to planetology are foreseen: camera, spectrometer, dust and particle detectors, and magnetometer. Depending on the ones kept, the mission could provide information on the gravity field, the atmosphere and the magnetosphere of the two bodies as well as on the surface geology of Triton and on the nature of the planetary rings around Neptune.

gr-qc↗

arXiv2011

Casimir and short-range gravity tests

Comparison with theory of Casimir force measurements are used to test the gravity force law at ranges from 0.1 to 10 micrometers. The interest of such tests depends crucially on the theoretical evaluation of the Casimir force in realistic experimental configurations. We present the scattering approach which is nowadays the best tool for such an evaluation. We then describe the current status of the comparisons between theory and experiments.

quant-ph↗

arXiv2011

Testing the Gravitational Redshift with Atomic Gravimeters?

gr-qc↗

arXiv2011

Radioscience simulations in General Relativity and in alternative theories of gravity

In this communication, we focus on the possibility to test GR with radioscience experiments. We present a new software that in a first step simulates the Range/Doppler signals directly from the space time metric (thus in GR and in alternative theories of gravity). In a second step, a least-squares fit of the involved parameters is performed in GR. This software allows one to get the order of magnitude and the signature of the modifications induced by an alternative theory of gravity on radioscience signals. As examples, we present some simulations for the Cassini mission in Post-Einsteinian gravity and with the MOND External Field Effect.

gr-qc↗

arXiv2011

Does an atom interferometer test the gravitational redshift at the Compton frequency ?

Atom interferometers allow the measurement of the acceleration of freely falling atoms with respect to an experimental platform at rest on Earth's surface. Such experiments have been used to test the universality of free fall by comparing the acceleration of the atoms to that of a classical freely falling object. In a recent paper, Müller, Peters and Chu [Nature {\bf 463}, 926-929 (2010)] argued that atom interferometers also provide a very accurate test of the gravitational redshift when considering the atom as a clock operating at the Compton frequency associated with the rest mass. We analyze this claim in the frame of general relativity and of different alternative theories. We show that the difference of "Compton phases" between the two paths of the interferometer is actually zero in a large class of theories, including general relativity, all metric theories of gravity, most non-metric theories and most theoretical frameworks used to interpret the violations of the equivalence principle. Therefore, in most plausible theoretical frameworks, there is no redshift effect and atom interferometers only test the universality of free fall. We also show that frameworks in which atom interferometers would test the redshift pose serious problems, such as (i) violation of the Schiff conjecture, (ii) violation of the Feynman path integral formulation of quantum mechanics and of the principle of least action for matter waves, (iii) violation of energy conservation, and more generally (iv) violation of the particle-wave duality in quantum mechanics. Standard quantum mechanics is no longer valid in such frameworks, so that a consistent interpretation of the experiment would require an alternative formulation of quantum mechanics. As such an alternative has not been proposed to date, we conclude that the interpretation of atom interferometers as testing the gravitational redshift is unsound.

gr-qc↗

arXiv2011

Casimir interaction between a dielectric nanosphere and a metallic plane

We study the Casimir interaction between a dielectric nanosphere and a metallic plane, using the multiple scattering theory. Exact results are obtained with the dielectric described by a Sellmeier model and the metal by a Drude model. Asymptotic forms are discussed for small spheres, large or small distances. The well-known Casimir-Polder formula is recovered at the limit of vanishingly small spheres, while an expression better behaved at small distances is found for any finite value of the radius. The exact results are of particular interest for the study of quantum states of nanospheres in the vicinity of surfaces.

quant-ph↗

arXiv2010

Casimir-Polder interaction between an atom and a dielectric grating

We develop the scattering approach to calculate the exact dispersive Casimir-Polder potential between a ground-state atom and a rectangular grating. Our formalism allows, in principle, for arbitrary values of the grating amplitude and period, and of the atom-grating distance. We compute numerically the potential for a Rb atom on top of a Si grating and compare the results with the potential for a flat surface taken at the local atom-surface distance (proximity force approximation). Except for very short separation distances, the potential is nearly sinusoidal along the direction transverse to the grooves.

quant-ph↗

arXiv2010

Driving quantized vortices with quantum vacuum fluctuations

We propose to use a rotating corrugated material plate in order to stir, through the Casimir-Polder interaction, quantized vortices in an harmonically trapped Bose-Einstein condensate. The emergence of such vortices within the condensate cannot be explained with a computation of the Casimir-Polder potential based on the pairwise summation approach or on the proximity force approximation. It thus appears as a genuine signature of non-trivial geometry effects on the electromagnetic vacuum fluctuations, which fully exploits the superfluid nature of the sample. In order to discuss quantitatively the generation of Casimir-driven vortices, we derive an exact non-perturbative theory of the Casimir-Polder potential felt by the atoms in front of the grating. Our numerical results for a Rb condensate close to a Si grating show that the resulting quantum vacuum torque is strong enough to provide a contactless transfer of angular momentum to the condensate and generate quantized vortices under realistic experimental conditions at separation distances around $3$ microns.

cond-mat.quant-gas↗

arXiv2010

Atom gravimeters and gravitational redshift

In a recent paper, H. Mueller, A. Peters and S. Chu [A precision measurement of the gravitational redshift by the interference of matter waves, Nature 463, 926-929 (2010)] argued that atom interferometry experiments published a decade ago did in fact measure the gravitational redshift on the quantum clock operating at the very high Compton frequency associated with the rest mass of the Caesium atom. In the present Communication we show that this interpretation is incorrect.

gr-qc↗

arXiv2010

Casimir effect in the scattering approach: correlations between material properties, temperature and geometry

We present calculations of the quantum and thermal Casimir interaction between real mirrors in electromagnetic fields using the scattering approach. We begin with a pedagogical introduction of this approach in simple cases where the scattering is specular. We then discuss the more general case of stationary arbitrarily shaped mirrors and present in particular applications to two geometries of interest for experiments, that is corrugated plates and the plane-sphere geometry. The results nicely illustrate the rich correlations existing between material properties, temperature and geometry in the Casimir effect.

quant-ph↗

arXiv2010

Thermal Casimir effect for Drude metals in the plane-sphere geometry

We compute the Casimir interaction between a plane and a sphere, the configuration employed in the most precise experiments. The scattering formula is developed by taking a suitably chosen plane-wave and multipole basis and is valid for arbitrary values of the sphere radius, inter-plate distance, temperature and arbitrary dielectric functions for both sphere and plate. Our analytical and numerical results for metallic surfaces show a non-trivial interplay between the effects of curvature, temperature, finite conductivity and dissipation.

quant-ph↗

arXiv2009

Thermal Casimir Effect in the Plane-Sphere Geometry

The thermal Casimir force between two metallic plates is known to depend on the description of material properties. For large separations the dissipative Drude model leads to a force a factor of 2 smaller than the lossless plasma model. Here we show that the plane-sphere geometry, in which current experiment are performed, decreases this ratio to a factor of 3/2, as revealed by exact numerical and large distance analytical calculations. For perfect reflectors, we find a repulsive contribution of thermal photons to the force and negative entropy values at intermediate distances.

quant-ph↗

arXiv2009

Quantum dissipative Brownian motion and the Casimir effect

We explore an analogy between the thermodynamics of a free dissipative quantum particle and that of an electromagnetic field between two mirrors of finite conductivity. While a free particle isolated from its environment will effectively be in the high-temperature limit for any nonvanishing temperature, a finite coupling to the environment leads to quantum effects ensuring the correct low-temperature behavior. Even then, it is found that under appropriate circumstances the entropy can be a nonmonotonic function of the temperature. Such a scenario with its specific dependence on the ratio of temperature and damping constant also appears for the transverse electric mode in the Casimir effect. The limits of vanishing dissipation for the quantum particle and of infinite conductivity of the mirrors in the Casimir effect both turn out to be noncontinuous.

quant-ph↗

arXiv2009

Casimir interaction between plane and spherical metallic surfaces

We give an exact series expansion of the Casimir force between plane and spherical metallic surfaces in the non trivial situation where the sphere radius $R$, the plane-sphere distance $L$ and the plasma wavelength $λ_¶$ have arbitrary relative values. We then present numerical evaluation of this expansion for not too small values of $L/R$. For metallic nanospheres where $R, L$ and $λ_¶$ have comparable values, we interpret our results in terms of a correlation between the effects of geometry beyond the proximity force approximation (PFA) and of finite reflectivity due to material properties. We also discuss the interest of our results for the current Casimir experiments performed with spheres of large radius $R\gg L$.

quant-ph↗

arXiv2009

Dispersive interactions between atoms and non planar surfaces

We calculate the dispersive force between a ground state atom and a non planar surface. We present explicit results for a corrugated surface, derived from the scattering approach at first order in the corrugation amplitude. A variety of analytical results are derived in different limiting cases, including the van der Waals and Casimir-Polder regimes. We compute numerically the exact first-order dispersive potential for arbitrary separation distances and corrugation wavelengths, for a Rubidium atom on top of a silicon or gold corrugated surface. We discuss in detail the inadequacy of the proximity force approximation, and present a simple but adequate approximation for computing the potential.

quant-ph↗

arXiv2008

Mass, inertia and gravitation

We discuss some effects induced by quantum field fluctuations on mass, inertia and gravitation. Recalling the problem raised by vacuum field fluctuations with respect to inertia and gravitation, we show that vacuum energy differences, such as Casimir energy, do contribute to inertia. Mass behaves as a quantum observable and in particular possesses quantum fluctuations. We show that the compatibility of the quantum nature of mass with gravitation can be ensured by conformal symmetries, which allow one to formulate a quantum version of the equivalence principle. Finally, we consider some corrections to the coupling between metric fields and energy-momentum tensors induced by radiative corrections. Newton gravitation constant is replaced by two different running coupling constants in the sectors of traceless and traced tensors. There result metric extensions of general relativity, which can be characterized by modified Ricci curvatures or by two gravitation potentials. The corresponding phenomenological framework extends the usual Parametrized Post-Newtonian one, with the ability to remain compatible with classical tests of gravity while accounting for new features, such as Pioneer like anomalies or anomalous light deflection.

gr-qc↗

arXiv2008

The Casimir effect in the nanoworld

The Casimir effect is a force arising in the macroscopic world as a result of radiation pressure of vacuum fluctuations. It thus plays a key role in the emerging domain of nano-electro-mechanical systems (NEMS). This role is reviewed in the present paper, with discussions of the influence of the material properties of the mirrors, as well as the geometry dependence of the Casimir effect between corrugated mirrors. In particular, the lateral component of the Casimir force and restoring torque between metal plates with misaligned corrugations are evaluated.

quant-ph↗