Tidal dynamics of extended bodies in planetary systems and multiple stars

With the discovery during the past decade of a large number of extrasolar planets orbiting their parent stars at a distance lower than 0.1 astronomical unit (and the launch and the preparation of dedicated space missions such as CoRoT and KEPLER), with the position of inner natural satellites around giant planets in our Solar System and with the existence of very closed but separated binary stars, tidal interaction has to be carefully studied. In particular, a question arises about the validity of usual approximations used in the modelling of this interaction. The purpose of this paper is to examine the step beyond the ponctual approximation for the tidal perturber. To achieve this aim, the gravitational interaction between two extended bodies and more precisely the interaction between mass multipole moments of their gravitational fields and the associated tidal phenomena are studied. Use of Cartesian Symmetric Trace Free (STF) tensors, of their relation with spherical harmonics and of the Kaula's transform enables to derive analytically the tidal and mutual interaction potentials as well as the associated disturbing functions in extended bodies systems. The tidal and mutual interaction potentials of two extended bodies are derived. Next, the external gravitational potential of such tidally disturbed extended body is obtained, using the Love's number theory, as well as the associated disturbing function. Finally, the dynamical evolution equations for such systems are given in their more general form without any linearization. The dynamical equations for the gravitational and tidal interactions between extended bodies and associated dynamics are derived in a form where they could be directly implemented to perform coherent numerical simulations of planetary systems or multiple stars tidal evolution.Comment: accepted for publication in Astronomy and Astrophysic

Influence of mass multipole moments on the deflection of a light ray by an isolated axisymmetric body

Future space astrometry missions are planned to measure positions and/or parallaxes of celestial objects with an accuracy of the order of the microarcsecond. At such a level of accuracy, it will be indispensable to take into account the influence of the mass multipole structure of the giant planets on the bending of light rays. Within the parametrized post-Newtonian formalism, we present an algorithmic procedure enabling to determine explicitly this influence on a light ray connecting two points located at a finite distance. Then we specialize our formulae in the cases where 1) the light source is located at space infinity, 2) both the light source and the observer are located at space infinity. We examine in detail the cases where the unperturbed ray is in the equatorial plane or in a meridian plane.Comment: 9 pages. Submitted to Physical Review

Spacetime-symmetry breaking effects in gravitational-wave generation at the first post-Newtonian order

Current searches for signals of departures from the fundamental symmetries of General Relativity using gravitational waves are largely dominated by propagation effects like dispersion and birefringence from highly dynamic sources such as coalescing binary-black holes and neutron stars. In this paper we take steps towards probing the nature of spacetime symmetries in the generation stage of gravitational waves; by using a generic effective-field theory, we solve the modified Einstein equations order-by-order for a generic source, and we write down the the first Post-Newtonian corrections, which includes contributions from the spacetime-symmetry breaking terms. Choosing as the source a system of point particles allows us to write down a simple toy solution explicitly, and we see that in contrast to General Relativity, the monopolar and dipolar contributions are non-vanishing. We comment on the detectability of such signals by the Laser Interferometer Space Antenna (LISA) space mission, which has high signal-to-noise galactic binaries (which can be modelled as point particles) well inside its predicted sensitivity band, sources which are inaccessible for current ground-based detectors, and we also discuss the possibility of going beyond the quadrupole formula and the first Post-Newtonian order, which would reveal effects which could be probed by ground-based detectors observing coalescence events.Comment: 14 pages, 3 figure

Reexamining aspects of spacetime-symmetry breaking with CMB polarization

The linear polarization of the Cosmic Microwave Background (CMB) is highly sensitive to parity-violating physics at the surface of last scattering, which might cause mixing of E and B modes, an effect known as {\it cosmic birefringence}. This has until recently been problematic to detect due to its degeneracy with the instrument polarization miscalibration angle. Recently, a possible detection of a non-zero cosmic-birefringence angle was reported at $\beta={0.35^\circ}\pm 0.14^\circ$, where the miscalibration angle was simultaneously determined and subtracted from the analysis. Starting from this claim, we exploit a simple map of $\beta$ to the coupling constant of a parity-violating term in a generic effective-field theory for Lorentz and CPT violation. We show that the reported constraint on $\beta$ is consistent with current one-sided upper bounds from CMB studies of spacetime-symmetry breaking, and we discuss the implications and interpretation of this detection.Comment: 6 pages, no figure

Electromagnetic fields in compact binaries: a post-Newtonian approach

Galactic binaries, and notably double white dwarfs systems, will be a prominent source for the future LISA and Einstein Telescope detectors. Contrarily to the black holes observed by the current LIGO-Virgo-KAGRA network, such objects bear intense magnetic fields, that are naturally expected to leave some imprints on the gravitational wave emission. The purpose of this work is thus to study those imprints within the post-Newtonian (PN) framework, particularly adapted to double white dwarfs systems. To this end, we construct an effective action that takes into account the whole electromagnetic structure of a star, and then specify it to dipolar order. With this action at hand, we compute the acceleration and Noetherian quantities for generic electric and magnetic dipoles, at a relative 2PN order. Finally, focusing on physically relevant systems, we show that the magnetic effects on the orbital frequency, energy and angular momentum is significant, confirming previous works conclusions.Comment: 23 pages, no figure, supplementary material attached v2: references and acknowledgments update

Electromagnetic fields in compact binaries: post-Newtonian wave generation and application to double white dwarfs systems

The aim of this work is twofold: (i) to properly define a wave-generation formalism for compact-supported sources embedded in Einstein-Maxwell theory, relying on matched post-Newtonian and multipolar-post-Minkowskian expansions; (ii) to apply this formalism (which is valid for any type of post-Newtonian sources) to the case of two stars with constant and aligned magnetic dipoles, by computing the fluxes of energy and angular momentum to the next-to-leading order, as well as the gravitational amplitude modes. Assuming eccentric orbits, we derive the evolution of orbital parameters, as well as the observables of the system, notably the gravitational phase for quasi-circular orbits. Finally, we give some numerical estimates for the contribution of the magnetic dipoles for some realistic systems.Comment: 44 page

GETEMME: a mission to explore the martian satellites

International audienceGETEMME (Gravity, Einstein's Theory, and Exploration of the Martian Moons' Environment) is a proposition of mission towards martian's moons. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine laser range measurements to the Phobos and Deimos reflectors. Also, asynchronous two-way laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellites system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter β as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame

Time Transfer functions as a way to validate light propagation solutions for space astrometry

Given the extreme accuracy of modern space astrometry, a precise relativistic modeling of observations is required. Concerning light propagation, the standard procedure is the solution of the null-geodesic equations. However, another approach based on the Time Transfer Functions (TTF) has demonstrated its capability to give access to key quantities such as the time of flight of a light signal between two point-events and the tangent vector to its null-geodesic in a weak gravitational field using an integral-based method. The availability of several models, formulated in different and independent ways, must not be considered like an oversized relativistic toolbox. Quite the contrary, they are needed as validation to put future experimental results on solid ground. The objective of this work is then twofold. First, we build the time of flight and tangent vectors in a closed form within the TTF formalism giving the case of a time dependent metric. Second, we show how to use this new approach to obtain a comparison of the TTF with two existing modelings, namely GREM and RAMOD. In this way, we evidentiate the mutual consistency of the three models, opening the basis for further links between all the approaches, which is mandatory for the interpretation of future space missions data. This will be illustrated through two recognized cases: a static gravitational field and a system of monopoles in uniform motion.Comment: 16 pages, submitted to CQ