Marc-Thierry Jaekel

Motion Induced Radiation from a Vibrating Cavity

We study the radiation emitted by a cavity moving in vacuum. We give a quantitative estimate of the photon production inside the cavity as well as of the photon flux radiated from the cavity. A resonance enhancement occurs not only when the cavity length is modulated but also for a global oscillation of the cavity. For a high finesse cavity the emitted radiation surpasses radiation from a single mirror by orders of magnitude.

Testing the Newton law at long distances

Experimental tests of Newton law put stringent constraints on potential deviations from standard theory with ranges from the millimeter to the size of planetary orbits. Windows however remain open for short range deviations, below the millimeter, as well as long range ones, of the order of or larger than the size of the solar system. We discuss here the relation between long range tests of the Newton law and the anomaly recorded on Pioneer 10/11 probes.

Gravity tests in the solar system and the Pioneer anomaly

We build up a new phenomenological framework associated with a minimal generalization of Einsteinian gravitation theory. When linearity, stationarity and isotropy are assumed, tests in the solar system are characterized by two potentials which generalize respectively the Newton potential and the parameter γ of parametrized post-Newtonian formalism. The new framework has the capability to account for the Pioneer anomaly while preserving the compatibility of other gravity tests with general relativity.

Post-Einsteinian tests of linearized gravitation

The general relativistic treatment of gravitation can be extended by preserving the geometrical nature of the theory but modifying the form of the coupling between curvature and stress tensors. The gravitation constant is thus replaced by two running coupling constants which depend on scale and differ in the sectors of traceless and traced tensors. When calculated in the solar system in a linearized approximation, the metric is described by two gravitation potentials. This extends the parametrized post-Newtonian (PPN) phenomenological framework while allowing one to preserve compatibility with gravity tests performed in the solar system. Consequences of this extension are drawn here for phenomena correctly treated in the linear approximation. We obtain a Pioneer-like anomaly for probes with an eccentric motion as well as a range dependence of Eddington parameter γ to be seen in light deflection experiments.

Radioscience simulations in general relativity and in alternative theories of gravity

This paper deals with tests of general relativity (GR) in the Solar System using tracking observables from planetary spacecraft. We present a new software that simulates the Range and Doppler signals resulting from a given spacetime metric. This flexible approach allows one to perform simulations in GR as well as in alternative metric theories of gravity. The outputs of this software provide templates of anomalous residuals that should show up in real data if the underlying theory of gravity is not GR. Those templates can be used to give a rough estimation of constraints on additional parameters entering alternative theory of gravity and also signatures that can be searched for in data from past or future space missions aiming at testing gravitational laws in the Solar System. As an application of the potentiality of this software, we present some simulations performed for Cassini-like mission in post-Einsteinian gravity and in the context of MOND external field effect. We derive signatures arising from these alternative theories of gravity and estimate expected amplitudes of the anomalous residuals.

MOVEMENT AND FLUCTUATIONS OF THE VACUUM

Quantum fields possess zero-point or vacuum fluctuations which induce mechanical effects, namely generalized Casimir forces, on any scatterer. Symmetries of vacuum therefore raise fundamental questions when confronted with the principle of relativity of motion in vacuum. The specific case of uniformly accelerated motion is particularly interesting, in connection with the much debated question of the appearance of vacuum in accelerated frames. The choice of Rindler representation, commonly used in general relativity, transforms vacuum fluctuations into thermal fluctuations, raising difficulties of interpretation. In contrast, the conformal representation of uniformly accelerated frames fits the symmetry properties of field propagation and quantum vacuum and thus leads us to extend the principle of relativity of motion to uniform accelerations. Mirrors moving in vacuum with a non-uniform acceleration are known to radiate. The associated radiation reaction force is directly connected to fluctuating forces felt by motionless mirrors through fluctuation - dissipation relations. Scatterers in vacuum undergo a quantum Brownian motion which describes irreducible quantum fluctuations. Vacuum fluctuations impose ultimate limitations on measurements of position in space - time, and thus challenge the very concept of space - time localization within a quantum framework. For test masses greater than Planck mass, the ultimate limit in localization is determined by gravitational vacuum fluctuations. Not only positions in space - time, but also geodesic distances, behave as quantum variables, reflecting the necessary quantum nature of an underlying geometry.

Gravitational quantum limit for length measurements

Abstract We discuss a limit for sensitivity of length measurements which is due to the effect of vacuum fluctuations of the gravitational field. This limit is associated with irreducible quantum fluctuations of geodesic distances and it is characterized by a noise spectrum with an order of magnitude mainly determined by the Planck length. The gravitational vacuum fluctuations may (in an analysis restricted to questions of principle and when the measurement strategy is optimized) dominate fluctuations added by the measurement apparatus if macroscopic masses, i.e. masses larger than the Planck mass, are used.

Radar ranging and Doppler tracking in post-Einsteinian metric theories of gravity

The study of post-Einsteinian metric extensions of general relativity (GR), which preserve the metric interpretation of gravity while considering metrics which may differ from that predicted by GR, is pushed one step further. We give a complete description of radar ranging and Doppler tracking in terms of the time delay affecting an electromagnetic signal travelling between the Earth and a remote probe. Results of previous publications concerning the Pioneer anomaly are corrected and an annually modulated anomaly is predicted besides the secular anomaly. Their correlation is shown to play an important role when extracting reliable information from Pioneer observations. The formalism developed here provides a basis for a quantitative analysis of the Pioneer data, in order to assess whether extended metric theories can be the appropriate description of gravity in the solar system.

Post-Einsteinian tests of gravitation

Einstein gravitation theory can be extended by preserving its geometrical nature but changing the relation between curvature and energy–momentum tensors. This change accounts for radiative corrections, replacing the Newton gravitation constant by two running couplings which depend on scale and differ in the two sectors of traceless and traced tensors. The metric and curvature tensors in the field of the Sun, which were obtained in previous papers within a linearized approximation, are then calculated without this restriction. Modifications of gravitational effects on geodesics are then studied, allowing one to explore phenomenological consequences of extensions lying in the vicinity of general relativity. Some of these extended theories are able to account for the Pioneer anomaly while remaining compatible with tests involving the motion of planets. The PPN ansatz corresponds to peculiar extensions of general relativity which do not have the ability to meet this compatibility challenge.

Conformal Symmetry and Quantum Relativity

The relativistic conception of space and time is challenged by the quantum nature of physical observables. It has been known for a long time that Poincare symmetry of field theory can be extended to the larger conformal symmetry. We use these symmetries to define quantum observables associated with positions in space-time, in the spirit of Einstein theory of relativity. This conception of localization may be applied to massive as well as massless fields. Localization observables are defined as to obey Lorentz covariant commutation relations and in particular include a time observable conjugated to energy. While position components do not commute in the presence of a nonvanishing spin, they still satisfy quantum relations which generalize the differential laws of classical relativity. We also give of these observables a representation in terms of canonical spatial positions, canonical spin components, and a proper time operator conjugated to mass. These results plead for a new representation not only of space-time localization but also of motion.