arXiv subjects

Christophe Le Poncin-Lafitte

Publications and source records attributed to Christophe Le Poncin-Lafitte.

At least 19 recordsLinked to original sources

arXiv2026

Nonconservative Lie series: post-Newtonian binary dynamics at 2.5PN

We develop a Lie series perturbation method for solving the dynamics of nonconservative systems within the doubled phase-space Hamiltonian framework introduced in our previous work [PRE 113, 034137]. The procedure can be applied to a wide range of perturbed nonconservative systems which are not initially given by a Hamiltonian, by casting them into the doubled phase-space where the Lie method can be employed. As an application, we tackle the non-spinning $2.5$ post-Newtonian binary problem at leading dissipative order. Starting from the ADM radiation-reaction dynamics, we construct a resonant Birkhoff normal-form and the corresponding generator of the canonical transformation. Next, we establish an analytical perturbative solution accounting for both the long-term (secular) and short-term (oscillatory) temporal behavior, without performing a small-eccentricity expansion, for nondegenerate bound eccentric orbits. The secular piece is encoded in a resonant normal-form, and captures the long-term inspiral, reconstructing exactly the known Peters-Mathews relations for semi-major axis and eccentricity. The oscillatory piece completes the dynamics by supplying instantaneous, non-averaged corrections to the orbital parameters. Combined, the two pieces give a controlled, fully canonical description of the dissipative dynamics.

gr-qc↗

arXiv2026

NovaMoon: A Strategic Lunar Reference Station for Positioning, Timing, and Largely Enhanced Science in the Earth-Moon System

The renewed interest in lunar exploration and the development of future lunar communication and navigation services highlight the need for a precise, stable, and interoperable geodetic and timing infrastructure on the Moon. NovaMoon, proposed as a scientific and navigation payload for ESA's Argonaut lander, is designed as a lunar-based local differential, geodetic, and timing station supporting both operational needs in the Moon's south polar region and a broad range of scientific investigations. The payload integrates a lunar laser retroreflector, a Very Long Baseline Interferometry transmitter, a receiver for navigation signals compatible with LunaNet standards, high-stability atomic clocks, and direct-to-Earth radio links -- making it the first lunar station to co-locate multiple ranging, tracking, and timing techniques. NovaMoon will enable sub-metre to decimetre positioning, provide local differential corrections for lunar users, and ensure an accurate and stable realisation of position and time. Preliminary simulation studies show that this multi-technique dataset improves the lunar reference frame, orientation and ephemerides, and estimates of interior parameters like tidal response and core properties. NovaMoon will also provide the first long-duration physical realisation of a lunar time reference. Beyond its primary goals, it supports improved cartography, precise surface geolocation, and higher-resolution topography, contributing to safer landings and operations. It also enables new tests of fundamental physics, including constraints on relativity and possible deviations from classical gravity.

astro-ph.EP↗

arXiv2025

Hamiltonian treatment of non-conservative systems

We present a novel extension of Hamiltonian mechanics to nonconservative systems built upon the Schwinger-Keldysh-Galley double-variable action principle. Departing from Galley's initial-value action, we clarify important subtleties regarding boundary conditions, the emergence of the physical-limit trajectory, and the decomposition of the Lagrangian into conservative and dissipative sectors. Importantly, we demonstrate that the redundant doubled configuration space admits a gauge freedom at the level of the canonical momenta that leaves the physical dynamics unchanged. From a Legendre transform, we construct the corresponding family of gauge-related nonconservative Hamiltonians; we show that virtually any classical initial-value problem can be embedded on our enlarged symplectic manifold, supplying the associated Hamiltonian and Lagrangian functions explicitly. As a further contribution, we derive a completely equivalent linear ``Lie'' formulation of the double-variable action and Hamiltonian which streamlines computations and renders transparent many structural properties of the formalism.

physics.class-ph↗

arXiv2025

Perturbative black-hole and horizon solutions in gravity with explicit spacetime-symmetry breaking

In this paper, we present static and spherically symmetric vacuum solutions to the mass-dimension $d\leq 4$ action of an effective-field theory, choosing the diffeomorphism symmetry to be broken explicitly. By using the reduced-action method with a Schwarzschild seed-solution, we find static and spherically symmetric black hole solutions to the field equations to linear order in the symmetry-breaking coefficients, which are consistent solutions to the modified Einstein equations at the same order. Using several ansätze for the symmetry-breaking coefficient we classify the allowed solutions, and we compute standard consequences and observables, including horizons, thermodynamics, photon geodesics, and perihelion precession. We find that the horizon structure of some of our solutions are similar to the Reissner-Nordström case, and that several of them exhibit physical singularities at $r=2M$. We note in particular that introducing more than one non-zero coefficient for spacetime-symmetry breaking coefficient leads to a solution with three horizons; the aim is to obtain observables that can be confronted to black holes observational data.

gr-qc↗

arXiv2025

Gravitational-wave generation in the presence of Lorentz invariance violation

We solve the wave equation for gravitational waves emitted by compact objects systems using the Multipolar Post-Minkowskian (MPM) method, and in the presence of Lorentz invariance violating terms. We select a Lorentz-violating extension of General Relativity in the pure gravity sector, directly taken from the Standard Model Extension (SME) formalism, and derive the wave equation for metric perturbation from the modified Einstein equation. We solve it with the MPM method and compute the gauge-invariant Riemann tensor components governing the geodesic deviation. Finally we compare the leading order term of the perturbative scheme in the small SME coefficients, with the leading order of the General Relativity. We outline the benefits and difficulties of this method. All the results are given as functionals of a set of general PM moments that can be matched to the physical properties of the source. These results are a first step toward putting state-of-the-art constraints on symmetries violations with new gravitational wave detectors like LISA.

gr-qc↗

arXiv2025

Hamiltonian normal forms for the post-Newtonian binary problem

We revisit the dynamics of the post-Newtonian (PN) two-body problem for two inspiraling compact bodies. Starting from a matter-only reduced Hamiltonian, we present an adapted framework based on the Lie series approach, enabling the derivation of complete perturbative solutions within the conservative sector. Our framework supports both circular and eccentric orbits, and is applicable to any perturbation respecting rotational invariance and time-independence. In the context of the Arnowitt-Deser-Misner (ADM) canonical formalism, this includes up to at least 3PN order and local terms beyond. We provide an example application at 2PN, recovering classical periapsis advance and orbital period corrections, alongside the full orbital evolution in time coordinates. We discuss eventual extension to spinning and time-dependent systems.

gr-qc↗

arXiv2023

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 $β={0.35^\circ}\pm 0.14^\circ$, where the miscalibration angle was simultaneously determined and subtracted from the analysis. Starting from this claim, we exploit a simple map of $β$ 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 $β$ 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.

astro-ph.CO↗

arXiv2023

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.

gr-qc↗

arXiv2023

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.

gr-qc↗

arXiv2023

Secular dipole-dipole stability of magnetic binaries

The presence of strong large-scale stable magnetic fields in a significant portion of early-type stars, white dwarfs, and neutron stars is well established. Despite this, the origins of these fields remain unresolved, with leading propositions advocating fossil fields, mergers, and shear-driven dynamos as the main mechanism. A potential key for further insight could lie in the connection with binarity: notably, magnetism can play a role in the long-term orbital and rotational dynamics of binaries. In gravitational wave astronomy, the advanced sensitivity of upcoming detectors such as LISA and the Einstein Telescope will enable the characterisation of the orbital inspirals of compact systems, including their magnetic properties. A comprehensive understanding of the dynamics of magnetism in these systems is required for the interpretation of the gravitational wave signals and to avoid calibration biases. Furthermore, this knowledge can be used to create new magnetic population models and to provide insight into the nature of their internal fields. The aim of this study is to investigate the secular spin precession dynamics of binary systems under pure magnetic dipole interactions, focusing on stars with strong, stable, dipolar fields. We employ an orbit-averaging procedure for the spin equations and obtain an effective secular description. By minimising the magnetic energy, we derive the configurations of equilibrium. We show that among the four states, only one is stable, consisting of the spin and magnetic axes of one star reversed with respect to the companions', and orthogonal to the orbital plane. Our long-term stability results disagree with usual methods, which tend to neglect orbital motion. Finally, we provide analytical solutions for the system out of equilibrium, which can be used to derive secular orbital evolution in the context of gravitational wave astronomy.

astro-ph.SR↗

arXiv2023

Detection of magnetic galactic binaries in quasi-circular orbit with LISA

Laser Interferometer Space Antenna (LISA) will observe gravitational waves from galactic binaries (GBs) of white dwarfs or neutron stars. Some of these objects are among the most magnetic astrophysical objects in the Universe. Magnetism, by secularly disrupting the orbit, can eventually affect the gravitational waves emission and could then be potentially detected and characterized after several years of observations by LISA. Currently, the data processing pipeline of the LISA Data Challenge (LDC) for GBs does not consider either magnetism or eccentricity. Recently, it was shown [Bourgoin et al. PRD 105, 124042 (2022)] that magnetism induces a shift on the gravitational wave frequencies. Additionally, it was argued that, if the binary's orbit is eccentric, the presence of magnetism could be detected by LISA. In this work, we explore the consequences of a future data analysis conducted on quasi-circular and magnetic GB systems using the current LDC tools. We first show that a single eccentric GB can be interpreted as several GBs and this can eventually bias population studies deduced from LISA's future catalog. Then, we confirm that for quasi-circular orbits, the secular magnetic energy of the system can be inferred if the signal-to-noise ratio of the second harmonic is high enough to be detected by traditional quasi-monochromatic source searching algorithms. LISA observations could therefore bring new insights on the nature and origin of magnetic fields in white dwarfs or neutron stars.

astro-ph.HE↗

arXiv2022

Gravitational waves radiated by magnetic galactic binaries and detection by LISA

In the context of the future Laser Interferometer Space Antenna (LISA) mission, galactic binary systems of white dwarfs and neutron stars will represent the dominant source of Gravitational Waves (GWs) within the $10^{-4}-10^{-1}\,\mathrm{Hz}$ frequency band. It is expected that LISA will measure simultaneously, the GWs from more than ten thousands of these compact galactic binaries. The analysis of such a superposition of signals will represent one of the greatest challenge for the mission. Currently, in the LISA Datacode Challenge, each galactic binary is modeled as a quasi-monochromatic source of GWs. This corresponds to the circular motion of two point-masses at the 2.5 post-Newtonian approximation. If this picture is expected to be an accurate description for most of the galactic binaries that LSIA will detect, we nevertheless expect to observe eccentric systems with complex physical properties beyond the point-mass approximation. In this work, we investigate how a binary system of highly magnetic objects in quasi-circular orbit could affect the quasi-monochromatic picture of the GW signal detected by LISA. We demonstrate that the eccentricity generates additional frequency peaks at harmonics of the mean motion and that magnetism is responsible for shifting each frequency peak with respect to the case without magnetism. We provide analytical estimates and argue that LISA will be able to detect magnetism if it can measure the main peaks at two and three times the mean motion with a sufficient accuracy.

gr-qc↗

arXiv2022

Impact of magnetism on gravitational waves emitted by compact galactic binaries in quasi-circular orbits

The LISA (Laser Interferometer Space Antenna) mission will observe in the low frequency band from 0.1 mHz to 1 Hz. In this regime, we expect the galactic binaries to be the dominant (by number) sources of gravitational waves signal. Considering that galactic binaries are composed of the most magnetized astrophysical objects in the universe (i.e., the white dwarfs and the neutron stars), LISA is expected to bring new informations about the origin and the nature of magnetism inside degenerated stars. Currently, the data processing assumes that the galactic binary systems are non-magnetic and in circular orbits which can potentially biased the determination of the parameters of the sources and also the calibration of the detector. In this work, we investigate the impact of magnetism on gravitational waves emitted by compact galactic binaries assuming quasi-circular orbits.

gr-qc↗

arXiv2022

GENESIS: Co-location of Geodetic Techniques in Space

Improving and homogenizing time and space reference systems on Earth and, more directly, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1mm and a long-term stability of 0.1mm/year are relevant for many scientific and societal endeavors. The knowledge of the TRF is fundamental for Earth and navigation sciences. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the positions of continental and island reference stations, as well as the ground stations of tracking networks. Also, numerous applications in geophysics require absolute millimeter precision from the reference frame, as for example monitoring tectonic motion or crustal deformation for predicting natural hazards. The TRF accuracy to be achieved represents the consensus of various authorities which has enunciated geodesy requirements for Earth sciences. Today we are still far from these ambitious accuracy and stability goals for the realization of the TRF. However, a combination and co-location of all four space geodetic techniques on one satellite platform can significantly contribute to achieving these goals. This is the purpose of the GENESIS mission, proposed as a component of the FutureNAV program of the European Space Agency. The GENESIS platform will be a dynamic space geodetic observatory carrying all the geodetic instruments referenced to one another through carefully calibrated space ties. The co-location of the techniques in space will solve the inconsistencies and biases between the different geodetic techniques in order to reach the TRF accuracy and stability goals endorsed by the various international authorities and the scientific community. The purpose of this white paper is to review the state-of-the-art and explain the benefits of the GENESIS mission in Earth sciences, navigation sciences and metrology.

physics.ins-det↗

arXiv2022

On the principle of Astrometric Gravitational Wave Antenna

The direct detection of gravitational waves by ground-based optical interferometers has opened a new window in astronomy. Nevertheless, as these detectors are a combination of two Michelson-Morley like baselines, their sensitivity for determining the incident direction of a gravitational wave is quite weak compared to current high-precision of space astrometry. We therefore present a novel concept for a gravitational wave antenna in space that uses close pairs of point-like sources as natural sensors to record and characterize the very tiny variations in angular separations induced by a passing gravitational wave, thus operating complementarily to linear arm detectors and enabling to gain informations on the gravitational wave incoming direction. Indeed, the proposed astrometric gravitational wave observable builds on methods of relativistic astrometry that can substantially enhance the strength of gravitational wave signals by exploiting to the fullest the telescope optical resolution and, at same time, provide a powerful tool for identifying the direction to the sources that originated the gravitational wave by monitoring close pairs of stars. Furthermore, the use of two local-line-of-sights in a differential formulation avoids issues related to high order modeling of the local (Solar System) background geometry and the need for accurate satellite ephemeris and attitude.

gr-qc↗

arXiv2022

Impact of dipolar magnetic fields on gravitational wave strain by galactic binaries

White dwarfs (WDs) and neutron stars (NSs) are among the most magnetized astrophysical objects in the universe, with magnetic fields that can reach up to $10^9\,\mathrm{G}$ for WDs and up to $10^{15}\,\mathrm{G}$ for NSs. The galaxy is expected to be populated with approximately one hundred million of double WD and millions of NS-WD binaries. Throughout the duration of the mission, the Laser Interferometer Space Antenna (LISA) will observe gravitational waves (GWs) emitted simultaneously by more than ten thousand of such galactic binaries. In this paper, we investigate the effect of the magnetic dipole-dipole interaction on the GW signal emitted by magnetic galactic binaries. We derive the secular equations governing the orbital and rotational motion of these objects. Then, we integrate these equations both numerically and analytically. We conclude that the overall visible effect is an additional secular drift of the mean longitude. This drift is proportional to the product of the magnetic moments and is inversely proportional to the $7/2$ power of the semi-major axis. Finally, we show that, at zeroth-order in eccentricity, the magnetic dipole-dipole interaction shifts the main frequency of the gravitational strain measured by LISA.

gr-qc↗

arXiv2021

Faint objects in motion: the new frontier of high precision astrometry

Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of Earth-mass habitable worlds around the nearest stars, to distant Milky Way objects, and out to the Local Group of galaxies. As we enter the era of the James Webb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local Universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry missions: NEAT proposed for the ESA M3 opportunity, micro-NEAT for the S1 opportunity, and Theia for the M4 and M5 opportunities. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this White Paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review instrumentation and mission profiles.

astro-ph.IM↗

arXiv2021

Dipolar magnetic fields in binaries and gravitational waves

The LISA mission will observe gravitational waves emitted from tens of thousands of galactic binaries, in particular white dwarf binary systems. These objects are known to have intense magnetic fields. However, these fields are usually not considered as their influence on the orbital and rotational motion of the binary is assumed for being too weak. It turns out that magnetic fields modify the orbits, in particular their geometry with respect to the observer. In this work, we revisit the issue, assuming magnetostatic approximation, and we show how the magnetic fields within a binary system generate a secular drift in the argument of the periastron, leading then, to modifications of the gravitational waveforms that are potentially detectable by LISA.

gr-qc↗