Contexte expérimental
La communauté scientifique française est très investie dans la recherche sur les OG, et a porté des avancées majeures sur un large spectre de sujets, allant du développement des détecteurs à l’analyse et l’interprétation des observations astrophysiques, à la modélisation des formes d'ondes gravitationnelles et à l’étude de l’évolution de l’univers sur ses plus grandes échelles, aux tests de la physique fondamentale et de la physique nucléaire.
Autre que LIGO-Virgo-Kagra (fréquence caractéristique ~10 à 10^3 Hz), plusieurs grandes experiences sur les ondes gravitationnelles vont continuer à voir le jour, et avec les nouvelles données il y aura d'importants impacts sur la recherche dans les prochaine 10 années.
LIGO-Virgo-Kagra va commencer son O4 run (mai 2023) puis O5, et on peut s'attendre à (bien plus) O(1) evennement par jour.
A basses fréquences (10-9–10-7 Hz) IPTA va bientot sortir des données de 25 pulsars (si pas deja fait). Nançay Radio Telescope (NRT)
La France est aujourd’hui un des principaux contributeurs à LISA (lancement prévu en 2035, fréquences mHz) avec une communauté nombreuse et dynamique.
La France est aussi très impliquée dans le projet European, Einstein Telescope, futur détecteur 3G au sol (fréquences semblables à celles de LIGO-Virgo [un peu plus larges à bases frequences] , mais avec bien meilleure sensibilité). On pourra voir les OG émisses de sources individuelles à des redshift z ≲ 100.
Très forte implication dans l'interférométrie atomique, 0.1 Hz- 10Hz, voir ci-dessous.
Il est également important de souligner l’implication française dans les aspects de prédiction et suivi des signaux multi-messagers, à la fois du point de vue observationnel et théorique. Des équipes françaises jouent le rôle de leader dans le télescope SVOM, et dans les fédérations ENGRAVE et GRANDMA. Des avancées théoriques dans l’interprétation et la caractérisation de la physique des GRBs ont été obtenues.
Toutes ces données vont avoir un impact majeur sur l'astrophysique, la Cosmologie (primordiale et tardive), la cosmologie multi-messager, les théories de gravité, la formation des structures, search for physics beyond the standard model, dark matter searches etc.
Formes d'onde
Determination of wave forms from binary systems in GR:
developments to higher PN, with spins and tidal effects, all needed for future detectors especially LISA. Computation of both conservative equations of motion plus effects of gravitational radiation reaction. Computation of waveforms (modes, especially the dominant quadrupole mode 22) and flux balance equations for secular evolution of the binary.
Inclusion of eccentricity to higher PN, unbound hyperbolic orbits etc. Relation between unbound and bound (elliptical) orbits including tail effects.
Effective Field theory techniques, amplitudes. These, together with ``classical'' PN approach, will probably develop together. Develop dictionary between the two approaches. [e.g. Analysis of asymptotic symmetries: synergy between these symmetries at null infinity and the waveform. Important for non-linear- and spin- memory effects + tails. ]
Effective one body: under-developed in France, but crucial to match inspiral to ringdown waveforms and for practical implementation of data analysis.
Numerical relativity. Tremendous progress over the last decades. A field which is under-developed in France. Connection with the community working of neutron star equations of state.
Quasinormal modes to higher (second) order: more accurate prediction of the ringdown phase following binary black hole mergers and future tests of the black hole no-hair theorem of general relativity.
Recent progress on the gravitational self force problem for compact binaries, now solved numerically to second order in the mass ratio, in the simplest case of the quasi-circular inspiral of nonspinning binaries. Much work remains to be done to obtain accurate waveforms for generic orbits around a spinning black hole (Kerr black hole background spacetime).
Study of resonances in EMRIs (extreme mass ration inspirals), and whether or not they're sustainable or not, in the presence of a third perturbing body. Hamiltonian formulation of the binary dynamics, studies of the (non-)integrable nature of the motion and possibility of chaotic motion.
Tidal deformability of black holes in GR and alternative theories of gravity, impact on waveforms for EMRIs, tidally-induced multipole moments and test of the black hole no-hair theorem.
All these questions can be repeated in modified gravity theories, see
Théories de gravité, where there are many developments to refine. For the moment scalar-tensor theories (generalized Brans-Dicke) are the only ones with accurate waveforms predicted.
Wave forms from other individual sources: important to understand other possible GW signals (continuous waves, bursts, boson stars, other exotic possibilities etc): there could well be new discoveries in the next 10 years, and one needs to be prepared.
Astrophysics, Cosmology with GWs (and other messengers)
In the next decade the number of GW events which will be detected will rapidly increase.
O4 2023-2025 – order 1000-10^4 BBH and BNS
O5 2026-2028 – 10^5 BBH or more
O6? 2030-2032 – 10^6 BBH or more.
With this data, it should be possible to determine, amongst other things, the population of BH in the local universe (mass and redshift distribution), as well as test GR in the strong field regime to high precision.
Regarding Astrophysics and Cosmology:
Using individual sources to measure the Hubble constant and other cosmological parameters (e.g. equation of state of DE), see
cosmologie. Unless there are many GW events with EM counterparts, this goes necessarily hand in hand with astrophysics (Galaxy surveys, cross correlation with LSS, mass distribution of black holes…)
probing anisotropic expansion or the cosmological principle with GW data
Tests of the formation channels of compact objects
understanding GW lensing, crucial for interpreting data and extracting parameters from events at higher redshift.
Multi-messenger tidal disruption events (TDEs)
For analysis of all the data, dealing with overlapping signals etc, necessary to develop techniques of
Machine Learning, IA, Quantum Computing. Indeed, it will be necessary to develop very refined detection methods to separate the signal from the noise, especially in the case of space-based detectors but also for ET.
Stochastic GW background (SGWB). Need to understand the astrophysical background to then probe the cosmological one, and hence early universe cosmology. This cosmological SGWB can probe energy scales where the universe is opaque to EM radiation, and hence is particularly exciting.
Calculation of templates, particularly for LISA. Different early universe sources e.g.: phase transitions, primordial BH, inflation – including the reheating phase –, cosmic strings, etc
These sources can also be probed in different frequency bands (PTA, LISA, ET, CE, LIGO…), so giving a broader picture.
Fluctuations of the SGWB.
Multi wavelength analysis (LIGO-VIRGO/LISA etc)
Dark matter and primordial black holes. GW bursts at high redshifts.
Etude des corrélations croisées entre les cartes des grands relevés de
Cosmologie et celles des
Ondes Gravitationnelles pour comprendre l'origine des systèmes binaires de trous noirs (stellaires, primordiaux…) ou le rôle des trous noirs supermassifs dans la formation des galaxies
Dark energy/modified gravity tests, tests of the propagation of GWs, e.g. modified dispersion relations, speed of GWs etc, see
Théories de gravité.
Probing the QCD equation of state with neutron stars, using both inspiral (equilibrium) and ringdown (out of equilibrium) phases. With Virgo_nEXT, ET, expect new results. CompOSE data tables developed in France. See also
particle physics. Note that multimessenger signals from neutron star mergers also contribute to understanding QCD but they need important new calculations of neutrino transport that contributes to the rapid cooling after mergers and controls what is emitted afterwards
Impact on astrophysics: GWs + other experiments (p.ex EHT) could confirm existence of super-massive BHs, and their abundance and mass distribution. How are they formed? Idem for stellar and intermediate mass black holes. LISA in particular will probe the BHB population in a wide mass range at different stages of the binary evolution, leading to constraints on the population and formation of BHB: indeed essentially *all* massive binary black holes with mass between 10^4-10^7 Msun will be seen, at every redshift: constraints on population, formation, environment (if with counterpart), probe of structure formation (galactic mergers)
Le développement d'interféromètres atomiques à grandes échelles est au centre de nombreuses grandes initiatives nationales pour les technologies quantiques : MIGA (FR), VLBAI (GER), MAGIA (IT), AION (UK National Quantum Technology Hub), MAGIS (USA).
Systèmes de Référence Temps-Espace, Laboratoire Kastler Brossel, Institut d'Otpique, Laboratoire Collisions Agrégats Réactivité