Théorie, Univers et Gravitation -- TUG

5 nov. 2024, 09:00 → 7 nov. 2024, 19:00 Europe/Paris

Auditorium (LAPTh)

philippe brax (IPHT Saclay), Marc Geiller (CNRS, ENS de Lyon), Katarina Kraljic, Julien Lavalle (LUPM - Montpellier), karim Noui (IJCLab, Paris Saclay University), Pasquale Dario Serpico (LAPTh, Annecy-le-vieux), Vincent Vennin (LPENS Paris)

Map to reach LAPTh

[English version below].

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Suite aux succès des précédents ateliers, nous souhaitons à nouveau réunir les chercheurs impliqués en "Théorie, Univers et Gravitation" pour faire un bilan des activités théoriques et phénoménologiques à l'échelle nationale sur ce domaine scientifique très large. Cet atelier sera l'occasion de présenter les développements récents dans nos différentes disciplines de manière transverse, tout en laissant place à des incursions plus techniques dans chacun des sujets couverts. Nous privilégierons à nouveau autant que possible la participation des jeunes chercheurs et chercheuses (nous pourrons participer aux frais de déplacement et de séjour dans la limite de notre budget).

Les grandes thématiques traitées comprendront notamment: Gravitation, Energie Noire, Grandes Structures, Univers Primordial, Matière Noire. Parmi les conférenciers confirmés figurent : G. Bélanger, J. Ben Achour, L. Bernard, S. Colombi, G. Cusin, C. Deffayet, C. Heissenberg, A. Held, E. Livine, J. Mazza, G. Moultaka, M. Petropoulos, Y. Rasera, C. Ringeval, D. Trestini, P. Zhang. 

Cet atelier se déroulera au LAPTh à Annecy  du 5 au 7 novembre 2024. Le 6/11 une partie de la matinée et de l'après-midi seront consacrées à une session hybride croisée avec les Journées Théorie de la communauté Hautes Énergies, qui auront lieu à Paris presque simultanément, concernant des thématiques d'intérêt commun, telles que les ondes gravitationnelles, gravité en champ fort, matière noire et interactions fondamentales.

Cet atelier est financé en partie grâce aux soutiens des PNCG, PNGRAM, de l'IN2P3, ainsi que du LAPTh, de l'Université Savoie-Mont Blanc et du LUPM.

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Boosted by the success of the previous editions of this workshop (series), we wish to bring again together researchers involved in the topics of "Theory, Universe, and Gravitation", to review the current theoretical or phenomenological developments carried out in groups working in or connected to French institutes. This workshop is meant to discuss these topics from different perspectives, different fields or approaches, with room for both pedagogical reviews and more technical talks. We encourage the participation of young researchers (a fraction of our budget will be allocated to partly support their travel expenses).

The big topics of this workshop comprise: Gravitation, Dark Energy, Large-scale Structures, Primordial Universe, Dark Matter. Confirmed speakers include: G. Bélanger, J. Ben Achour, L. Bernard, S. Colombi, G. Cusin, C. Deffayet, C. Heissenberg, A. Held, E. Livine, J. Mazza, G. Moultaka, M. Petropoulos, Y. Rasera, C. Ringeval, D. Trestini, P. Zhang. 

This workshop will take place at LAPTh, Annecy-le-Vieux, from Nov. 5 to Nov. 7, 2024. On 6/11, part of the morning and afternoon will be devoted to a crossed hybrid session with the  Journées Théorie de la communauté Hautes Énergies,  held in Paris almost simultaneously, concerning themes of common interest such as gravitational waves, strong field gravity, dark matter and fundamental interactions.

Supporting funding agencies include PNCG, PNGRAM, IN2P3, LAPTh, Université Savoie-Mont Blanc, and LUPM.

 

 

*** Important: Registration and participation require a valid academic affiliation at the time of registration and at the time of the workshop (Master students registered at a University at the time of application are eligible, pending a valid affiliation at the time of the event). Selection further requires a close scientific contact with French institutes, as this workshop is meant to structure the community at the national level. We reserve the right to reject any application which does not comply with the above criteria. Please contact the organizers in case you think your apllication has been mistakenly rejected. Non-affiliated persons are not allowed to participate in the event for insurance reasons, even if they passed the registration filter.

mardi 5 novembre

09:20 → 09:40 Welcome

09:40 → 10:10 Gravity from its symmetries

Orateur: Jibril BEN ACHOUR (ENS de Lyon / Arnold Sommerfeld Center (Munich))

10:10 → 10:30 Relativity of the event: examples in JT gravity

Gravitational gauge constraints imply that local, bulk, measurable operators must be dressed to a fixed reference surface with the worldlines of some observers. Since observers live in their own inertial coordinate systems, they are unable to distinguish between different branches of the wavefunction when the metric is in superposition, and will identify the outcome of their measurement, whatever it is, as a single event occurring at a particular location. In the inertial frame of another set of observers, however, the event of this measurement will be identified as occurring in different locations according to the state of the metric. An event at a definite location for one set of observers will therefore be in a superposition of locations for another set of observers. We quantify an example of this effect in JT gravity, where certain observers see the black hole horizon as "smeared".

Orateur: Alexander TASKOV (CPT)

10:30 → 10:50 The operational meaning of total energy in general relativity

The ADM and Bondi energies are key examples of diffeomorphism-invariant observables. They have played a crucial role to understand energy in general relativity, and by Noether's theorem, to understand (boundary) symmetries. In spite of their conceptual importance, we don't know how to directly measure them: their reconstructed values from gravitational waveforms are only inferred quantities. In this talk I will present thought experiments that provide an operational meaning to both ADM and Bondi energies.

Orateur: Simone Speziale (CPT Marseille, CNRS)

10:50 → 11:10 Coffee break

11:10 → 11:40 Black holes in theories beyond general relativity

Orateur: Jacopo Mazza

11:40 → 12:00 Towards the measurement of entanglement from superradiance in rotating geometries

Quantum effects of fields on curved spacetimes may be studied in the laboratory thanks to quantum fluids via `analogue gravity'. In this talk, I will review the theoretical foundations of analogue gravity with fluid systems before focusing on the specific case of rotational superradiance. This manifests as the correlated emission of paired excitations of the acoustic field at the acoustic ergosurface in a vortex fluid flow. I will then introduce our experimental platform [1,2]: quantum fluids of polaritons, composite bosons resulting from the strong coupling of laser light confined in a cavity with semiconductor excitons. Polaritons are intrinsically out of thermal equilibrium, which not only bears experimental advantages over other quantum fluids [1,2] but should also permit the observation of new field effects [3]. I will explain how to create stable ergosurfaces without horizons inside (an experimental first!) with polaritons and review recent experimental results on rotational superradiance in this platform. This will open a discussion on the possibility to generally study the dynamics of entanglement from ergosurfaces and horizons on bespoke curved spacetimes [4].

[1] Jacquet M et al., Analogue quantum simulation of the Hawking effect in a polariton superfluid. EPJD 76 152 (2022)
[2] Falque K et al., Measurement of field theories on bespoke curved spacetimes in a polaritonic fluid of light. arxiv:2023.01392
[3] Jacquet M et al., Quantum vacuum excitation of a quasi-normal mode in an analog model of black hole spacetime, PRL 130 111501 (2023)
[4] Delhom A et al., Entanglement from superradiance and rotating fluids of light. PRD 109 105024 (2024)

Orateur: Maxime Jacquet (Laboratoire Kastler Brossel, CNRS France)

12:00 → 12:20 Algebraically special quadratic Schwarzschild perturbations

The equations describing linear perturbations around a Schwarzschild black hole admit analytical solutions that describe waves of specific wavelengths propagating outside the black hole. While perturbations around a Schwarzschild black hole are generally of Petrov type I, these analytical solutions describe spacetimes of Petrov type II, and are thus dubbed 'algebraically special modes'. The existence of these modes is linked to the isospectrality theorem for Schwarzschild. In this work, I go beyond the linear approximation and construct algebraically special perturbations around a Schwarzschild black hole at the quadratic order, making use of a family of exact twisting vacuum radiative solutions of General Relativity. These quadratic perturbations can still be expressed analytically, similarly to their linear sources. I study their properties and show in particular how static quadratic perturbations deform the Schwarzschild black hole.

Orateur: Hugo Roussille (École Normale Supérieure de Lyon)

12:20 → 14:00 Lunch break

14:00 → 14:30 Spinfoam models for quantum gravity

Orateur: Etera Livine (ENS-Lyon)

14:30 → 15:00 Numerical Relativity in effective field theories of gravity

The age of gravitational-wave astronomy is now in full swing: For the first time, we gain observational access to the highly dynamical strong-field regime of the gravitational interaction. Constraining potential deviations from General Relativity (GR) requires reliable waveform predictions, not just in GR, but also when higher curvature corrections contribute to the dynamics. I will present an overview of recent progress on
(i) mathematical well-posedness,
(ii) physical time evolution in the presence of ghosts, and
(iii) resulting numerical nonlinear waveforms.
In combination, the above constitutes a feasible pathway to use current and future gravitational-wave observations to constrain effective field theories of gravity. The same methods may also be applied to address higher-curvature corrections in the early universe.

Orateur: Aaron Held

15:00 → 15:20 Vanishing of Quadratic Love Numbers of Schwarzschild Black Holes

The static tidal response of compact objects is characterized by tidal Love numbers, which provide insights into the black hole horizon or the internal structure of compact objects. These numbers can be directly extracted from gravitational wave measurements of compact binaries. It is well-known that asymptotically flat Schwarzschild black holes in general relativity, in four spacetime dimensions, exhibit a vanishing static induced linear tidal response. In this talk, I will extend this result to the quadratic response under an arbitrary static tidal field. By matching the second-order black hole perturbation calculations to point-particle effective theory, we demonstrate that the nonlinear Love numbers describing the quadratic response also vanish. I will discuss the implications of this result for black hole perturbation theory and gravitational wave phenomenology.

Orateur: M. Nikola Savic (IPhT Paris)

15:20 → 15:50 Coffee break

15:50 → 16:20 Carroll and flat holography

The theme of asymptotically flat spacetimes has come back recently to the fore, fueled by the discovery of gravitational waves and the growing interest in what flat-space holography could be. In this quest, Carrollian geometry plays a central role. After outlining a synoptic survey of Carrollian geometric structures, I will show how Ricci-flat spacetimes are generally reached as a limit of Einstein geometries and how they are in fact constructed by means of an infinite set of data data defined on the conformal Carrollian boundary that is null infinity, and emerging as the coefficients of the Laurent expansion of the energy-momentum tensor in powers of the cosmological constant. Comparison with the celestial approaches is part of the agenda.

Orateur: Marios Petropoulos (CPhT Palaiseau)

16:20 → 16:40 Mock modularity of Calabi-Yau threefolds

Generating functions h(τ ) of D4-D2-D0 BPS indices, appearing in Calabi-Yau compactifications of type IIA string theory and identical to rank 0 Donaldson-Thomas invariants,are known to be higher depth mock modular forms satisfying a specific modular anomaly, with depth dtermined by the D4-brane charge r. We develop a mmethod to solve the modular anomaly equation for arbitrary charges, in terms of indefinite theta series.
This allows to find the generating functions up to modular forms that can be fixed by computing just a finite number of Fourier coefficients of h.

Orateur: Khalil Bendriss (L2C)

16:40 → 17:10 Bohmian mechanics and bouncing universes

Orateur: Dr Gilbert Moultaka (CNRS - LUPM (Montpellier))

17:10 → 17:30 Dark energy in string theory models

I will discuss various attempts to reproduce dark energy in cosmological models derived from string theory, either in the form of a cosmological constant or with quintessence.

Orateur: Dr David Andriot (LAPTh, CNRS)

mercredi 6 novembre

09:00 → 09:30 N-body simulations as a tool for investigating the nature of dark energy and gravity at cosmological scales.

N-body simulations are a powerful tool for investigating the nature of dark energy and gravity at cosmological scale. In this talk, I will present new progress made in this field in two directions. Firstly, by launching billions of light rays inside light cones extracted from simulation volumes, it is now possible to use them as laboratories for studying general relativistic effects at cosmological scale. Secondly, by running thousands of simulations in modified gravity, it is possible to build emulators that allow fast and accurate predictions for the distribution of large-scale structures beyond general relativity.

Orateur: Yann RASERA (LUTH/Obs. de Paris/Univ. Paris Cité/IUF)

09:30 → 09:50 Covariant Cosmography with the Expansion Rate Fluctuations Field

Is it possible to construct a detailed model of local spacetime in a completely model-independent and non-perturbative manner? Specifically, this would involve developing an observationally viable and physically meaningful method for identifying and classifying angular distortions present in the distance-redshift relation, without relying on the cosmological principle or the notion of peculiar velocities.
The first difficulty along this path is the meaningful generalization of the notion of the cosmic expansion rate at an arbitrary point
P
in a generic spacetime. This involves defining covariant cosmographic parameters, which are a set of line-of-sight dependent functions, with finite degrees of freedom, characterizing deviations from isotropy and critically dependent on the observer's state of motion. The second challenge revolves around the optimal estimation of anisotropies in the expansion rate using observational data. To this end, we define the expansion rate fluctuation field η, an observable designed to maximize measurement accuracy while minimizing potential biases.

Using analytical models, we analyze the virtues and limitations of this formalism. Current results and future survey prospects for constraining the shape of the expansion rate field in the local universe will also be presented.

Orateur: Prof. Christian Marinoni (Centre de Physique Théorique, Aix-Marseille Univ.)

09:50 → 10:20 The formation of the first nonlinear dark matter structures in the universe

In the standard picture of cosmic structure formation, the first dark matter objects to form are expected to be microhalos of roughly Earth mass and solar system size. In this framework I will discuss how pancakes seed these primordial structures and how dark matter microhalos emerge through violent relaxation and the appearance of a power-law prompt cusp, then grow and relax to the so-called Navarro Frenk and White profile through subsequent infall and mergers.

Orateur: Stéphane Colombi

10:20 → 10:40 A self-similar approach to Dark Matter halo dynamics in 2D Vlasov simulations

Understanding dark matter halo dynamics can be pivotal to unravelling the nature of dark matter particles. Analytical treatment of the multistream flows inside the turn-around region of a collapsed CDM (cold dark matter) halo using various self-similar approaches already exist. In this work, we adapt the Fillmore and Goldreich self-similar solutions assuming cylindrical symmetry to data from 2D Vlasov-Poisson (ColdICE package) simulations of isolated halos seeded with sin-wave initial conditions. We measure trajectories in position and phase-space, mass and density profiles and compare these to predictions from the self-similar model, with an aim to establish the limits of self-similar behaviour and the factors leading to deviations from it.

Orateur: Abineet Parichha (Institut d'Astrophysique de Paris - Sorbonne Université)

10:40 → 11:10 Coffee break

11:10 → 11:40 The gravitational wave window on the universe

Orateur: Giulia Cusin (IAP)

11:40 → 12:10 Glory and fate of post-newtonian approaches to general relativity and beyond

Orateur: Laura Bernard (LUTH - CNRS / Observatoire de Paris)

12:10 → 12:30 Small-scale clustering of Primordial Black Holes

In this talk, based on arXiv:2402.00600, we revisit the initial spatial
clustering of Primordial Black Holes (PBHs) originating from the Hubble
reentry of large Gaussian density fluctuations in the early Universe.
Using an excursion-set approach, we derive the two-point correlation
functions of PBHs, properly accounting for the “cloud-in-cloud”
mechanism. Our expressions naturally and intrinsically correlate the
formation of pairs of PBHs, which is a key difference with the Poisson
model of clustering. Our approach effectively includes short-range
exclusion effects and clarifies the clustering behaviors at small scale:
PBHs are anticorrelated at short distances. Using a scale-independent
collapse threshold, we derive explicit expressions for the excess
probability to find pairs of PBHs, as well as the excess probability to
find pairs with asymmetric mass ratio. Our framework is model
independent by construction, and we discuss possible other applications.

Orateur: Pierre Auclair (UCLouvain)

12:30 → 14:00 Lunch break

14:00 → 14:30 Indirect dark matter searches (PNHE-TH)

Orateur: Silvia Manconi (LAPTh)

14:30 → 15:00 Equation of state of ultra dense matter in neutron stars (PNHE-TH)

Orateur: Anthea FANTINA ({CNRS}UPR3266)

15:00 → 15:20 Compact objects beyond general relativity as seen in the EHT images (PNHE-TH)

Orateur: Irene Urso (LESIA, Paris Observatory)

15:20 → 15:50 Coffee break

15:50 → 16:20 Inflation at the crossroads

mini-review

Orateur: Christophe Ringeval (CURL, UCLouvain)

16:20 → 16:40 Strong Mixing at the Cosmological Collider

Apart from its manifest interest in the understanding of the first moments of the universe, the framework of cosmic inflation is also the best way we know to probe fundamental physics at very high energies. In particular, the spontaneous production of massive particles due to the expanding background can leave potentially visible imprints in cosmological correlation functions known as the cosmological collider signal.
Within the effective field theory of inflation (EFTI), it is possible to treat these exchange processes in a model-independent way, and explicit computations taking advantage of the conformal invariance of late-time observables have been carried out using various techniques such as the cosmological bootstrap. More recently, the full parameter space allowed by the EFTI has been explored allowing for boost-breaking setups leading to more striking phenomenological signatures, and the recently developed cosmological flow approach numerically gives us access to any correlation function.
In this talk, I will expose a treatment of a parameter space region that remains analytically unknown: the strong mixing regime where the inflaton field and the massive particle can experience an infinite number of flavor transformations during the process. I will describe ongoing efforts to describe this regime based on extensions of standard single-field effective field theory techniques.

Orateur: Arthur Poisson (IAP)

16:40 → 17:00 Clocking the End of Inflation

Making observable predictions for cosmic inflation requires determining when the wavenumbers of astrophysical interest today exited the Hubble radius during the inflationary epoch. These instants are commonly evaluated using the slow-roll approximation and measured in e-folds $\Delta N=N−N_{\mathrm{end}}$​, in reference to the e-fold $N_{\mathrm{end}}$​ at which inflation ended. Slow roll being necessarily violated towards the end of inflation, both the approximated trajectory and $N_{\mathrm{end}}$​ are determined at, typically, one or two e-folds precision. Up to now, such an uncertainty has been innocuous, but this will no longer be the case with the forthcoming cosmological measurements. In this work, we introduce a new and simple analytical method, on top of the usual slow-roll approximation, that reduces uncertainties on $\Delta N$ to less than a tenth of an e-fold.

Orateur: Baptiste Blachier (CURL, UCLouvain and LPENS)

17:00 → 17:20 Revisiting the stochastic QCD axion window: departure from equilibrium during inflation

If dark matter is made of QCD axions, its abundance is determined by the vacuum expectation value acquired by the axion field during inflation. The axion is usually assumed to follow the equilibrium distribution arising from quantum diffusion during inflation. This leads to the so-called stochastic window under which the QCD axion can make up all the dark matter. However, in realistic inflationary potentials, I will show that the axion never reaches the equilibrium distribution at the end of inflation. This is because the relaxation time of the axion is much larger than the typical time scale over which $H$ varies during inflation. As a consequence, the axion acquires a quasi-flat distribution as long as it remains light during inflation. This leads to a reassessment of the stochastic axion window.

Orateur: Vadim Briaud (LPENS)

jeudi 7 novembre

09:00 → 09:30 Line intensity mapping in cosmology

mini-review

Orateur: Azadeh Moradinezhad (Laboratoire d'Annecy-le-Vieux de Physique Théorique (LAPTh))

09:30 → 10:00 Effective theory of the large scale structure of the universe

Orateur: Dr Pierre Zhang (ETH-Zurich)

10:00 → 10:20 Optimal constraints on Primordial non-Gaussianity with the eBOSS DR16 quasars in Fourier space

The statistical properties of the primordial curvature perturbations are a key ingredient of the success of the LCDM model in explaining the Universe as we observe it today. In simplest models of inflation initial fluctuations are Gaussian for all practical purposes, and measurements of the CMB bispectrum by the Planck satellite constrain any deviation from the Gaussian regime in a part in ten thousand. On the other hand, the theoretical target for the amplitude of Primordial Non-Gaussianities (PNG) in the initial perturbations is roughly an order of magnitude smaller than what Planck has measured. We have almost saturated the information content in the CMB, and any further improvement will likely come from the late-time distribution of galaxies or any other tracers of the Large Scale Structure (LSS) of the Universe.
I will present constraints on the amplitude of local PNG, $f_{\rm NL}$, using the quasar sample in the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 16 (DR16) from https://arxiv.org/abs/2309.15814. We analyze the power spectrum monopole, testing for the presence of scale-dependent galaxy bias induced by local PNG. Our analysis makes use of optimal redshift weights that maximize the response of the quasar sample to the possible presence of non-zero PNG. We find $-4

Orateur: Marina Cagliari (LAPTh)

10:20 → 10:40 Breaking the distance duality relation to explain the cosmic calibration tension

A “cosmic calibration tension” has been identified as the discrepancy between the cosmological distance ladder built from different distance observables (such as BAO and SN1a), which are calibrated using measurements from the early- or late-Universe. However, this assessment assumes that the distance-duality relationship (DDR) holds and can be used to compare measurements of the luminosity and angular diameter distances. In this talk, we will examine the implications of relaxing this assumption to more general relations, its implications to the current cosmic tensions and how it could potentially explain the apparent need for the introduction of new physics to address current cosmic tensions.

Orateur: Elsa Teixeira (LUPM Montpellier)

10:40 → 11:10 Coffee break

11:10 → 11:40 A post-LHC view of particle dark matter

Review talk on particle dark matter.

Orateur: Prof. Genevieve Belanger (LAPTH)

11:40 → 12:10 Searches for ultralight dark matter: from the lab to space

UltraLight Dark Matter (ULDM) is a class of bosonic Dark Matter candidates whose mass is below the electronVolt. Such Dark matter candidates have become very popular in the last decade, in particular because of the lack of direct detection of WIMPs with particles accelerators. The most studied ULDM candidates are the axion (pseudo-scalar particle), the dilaton (a scalar particle) and the hidden photon (a spin 1 particle). The phenomenology of ULDM is very rich and in particular, it can be searched for using atomic sensors like atomic clocks, cavities, atom interferometry, etc... In this talk, we will review the basic properties of such dark matter candidates and discuss some of their theoretical properties. We will then focus on experimental results and also present some new proposals of experiments specifically designed to search for such new fields.

Orateur: Aurelien Hees (SYRTE - Observatoire de Paris)

12:10 → 12:40 The price to pay for abandoning dark matter

Orateur: Cédric Deffayet (CNRS-LPENS)

12:40 → 14:00 Lunch break

14:00 → 14:30 An Eikonal Approach to Gravitational Bremsstrahlung

In this talk, I will discuss recent developments in the calculation of the gravitational waveform emitted during a scattering of two compact objects, considering two complementary regimes. The first is the post-Minkowskian (PM) approximation, where one focuses on widely separated objects, i.e. scatterings at large impact parameters. In this setup, interactions are weak and can be treated perturbatively. A particularly natural approach to attack this problem is to exploit the connection with scattering amplitudes, for which the eikonal framework offers a systematic way to describe the classical limit. I will discuss in particular how the next-to-leading PM waveform can be extracted from a one-loop 2->3 amplitude. The second approximation consists in focusing on low-frequency emissions, which are governed by universal soft theorems. These are simple relations that dictate in particular the structure of leading log-enhanced pieces of the type $\omega^{n-1}(\log\omega)^n$ for $n=0,1,2...$ in the low-frequency expansion, as $\omega\to0$. I will present a recent proposal for a resummation of all such terms and discuss their contribution to the energy emission spectrum.

Orateur: Carlo Heissenberg (IPhT)

14:30 → 15:00 Gravitational waves from quasielliptic compact binary systems in massless scalar-tensor theories

Post-Newtonian (PN) theory for inspiraling compact binary systems has been extremely successful in generating waveforms in general relativity (GR). However, if we are interested in testing GR, it would be very useful to have a bank of waveform templates for alternative theories of gravity as well. This program has already begun in a class of massless scalar-tensor theories (equivalent to DEF gravity), which is arguably one of the simplest alternative to GR. Previously, the equations of motion have been computed up to 3PN order [1-3], and the orbital phase has been computed for circular orbits up to 2.5PN beyond the leading dipolar order [4-7]. With the objective of widening the parameter space modeled, I will present in this talk recent advances for the case of elliptic orbits. First, I will present the post-Keplerian parametrization for quasielliptic motion up to 2PN order in scalar-tensor theories [8], and discuss how this can straightforwardly be adapted to other theories. I will show how this easily leads to obtaining the gravitational waveform at 1PN relative order for eccentric orbits [8]. Then, I will present ongoing work [9] aiming at increasing the accuracy of the waveform model. I will focus on the computation of the flux (radiated at infinity) of energy and angular momentum up to 2.5PN order, relatively to the leading dipolar radiation. These quantities exhibit a number of new difficulties, among which the presence of tails and memory contributions. Finally, I will discuss how to combine the post-Keplerian parametrization and these fluxes to deduce the secular evolution of the orbital parameters (e.g. the semimajor axis and eccentricity) through 2.5PN order. These physically correspond to the (modulated) chirp in the waveform frequency, which is a key observable for gravitational wave detectors.

[1] Mirshekari and Will, Phys. Rev. D 87, 084070 (2013), arXiv:1301.4680
[2] Bernard, Phys. Rev. D 98, 044004 (2018), arXiv:1802.10201
[3] Bernard, Phys. Rev. D 99, 044047 (2019), arXiv:1812.04169
[4] Lang, Phys. Rev. D 89, 084014 (2014), arXiv:1310.3320
[5] Lang, Phys. Rev. D 91, 084027 (2015), arXiv:1411.3073
[6] Sennett, Marsat and Buonanno, Phys.Rev.D 94, 084003 (2016), arXiv:1607.01420
[7] Bernard, Blanchet and Trestini, JCAP 08, 008 (2022), arXiv:2201.10924
[8] Trestini, Phys. Rev. D 109, 104003 (2024), arXiv:2401.06844
[9] Trestini (2024), in preparation

Orateur: David Trestini (IAP et LUTH)

15:00 → 15:20 Tidal contributions to the gravitational waveform amplitude to the second-and-a-half post-newtonian order

The study of tidal effects between compact objects such as neutron stars is particularly promising to better understand their physics. Including these effects in our waveform models could allow us to probe their internal structure, but also possibly to distinguish signals coming from black holes, neutron stars or even more exotic objects. This will be of paramount importance when interpreting the multiple signals expected with the arrival of third-generation gravitational wave detectors.
The tidal interaction affects both the dynamics and the gravitational wave emission processes of compact binaries resulting in a change in the orbital phase and the gravitational wave amplitude that are directly observable.
In this talk, I will present how we completed the computation of gravitational waveform amplitude modes using the post-Newtonian-multipolar-post-Minkowskian formalism with an order of accuracy of 2.5PN and wrote them in form suitable for effective-one-body template building.

Orateur: Eve Dones (LUTH - Observatoire de Paris)

15:20 → 15:40 Second order gravitational waves: paving the way for a full calculation.

Gravitational waves provide a new observational tool to study the universe. There has been extensive research on scalar induced gravitational waves (SIGWs), since they could be the counterpart signal of primordial black holes. SIGWs are sourced by terms quadratic in first order scalar fluctuations from inflation. In this talk, I will discuss the possibility and implication of including tensor fluctuations at first order in the source term. Furthermore, I will talk about the correlation of third order and first order gravitational waves and comment on the imprint this leaves on the spectral energy density. Finally, I will discuss implications for their detectability and observational constraints for models of inflation.

Orateur: Raphael Picard (Queen Mary University London)

15:40 → 16:00 Revisiting 2PN Hamiltonian mechanics of binary black holes

Accurate modeling of binary black hole (BBH) dynamics is crucial for the detection of gravitational waves emitted by them. We focus on the so-called "orbit-averaged" spinning BBH system at the second post-Newtonian (PN) order. We discover that it is a Hamiltonian system and we present its Hamiltonian. We then establish that it is an integrable system (one that possesses action-angle variables (AAVs)) owing to the already known constants of motion. We then construct its AAVs and hence its AAV-based solution. Using these AAVs, we locate some of its separatrices and resonances. Additionally, for the non-integrable 2PN system (without any orbit-averaging), we construct the solution for the magnitude of the position vector of the black-holes in the so-called quasi-Keplerian spirit, despite the non-integrability of the system.

Orateur: Dr Sashwat Tanay (LUTH, Paris Observatory)

16:00 → 16:30 Goodbye coffee