Scattering experiments are the most elaborate way to analyse the laws of nature. In quantum field theory, the S-matrix encompasses all scattering processes, and describes physical phenomena as varied as collision experiments, gravitational waves, the strong nuclear force, string theoretic and quantum gravitational effects such as black hole production in high-energy scattering. There are two approaches to compute the S-matrix: perturbative and non-perturbative. The first has progressed a lot, propelled by the modern colliders’ needs, but captures only restricted physical regimes. Interestingly, it gave rise to new concepts, such as the double-copy construction of gravity, whose origin is elusive. The non-perturbative approach aims to compute the S-matrix directly, by combining the powerful principles it must obey: unitarity, causality, and crossing. Its main bottlenecks are our lack of control on multi-particle processes, and the non-linear nature of unitarity. These constraints are so stringent that today we still have not obtained a single fully consistent S-matrix. This project aims to fill this gap. It will (1) provide the first fully consistent S-matrices and produce the most accurate up-to-date pion S-matrix model, (2) produce models of unitary quantum-gravity scattering with high-energy black hole production. Even more ambitiously, for (1) and (2), the team will explore the space of all such consistent S-matrices. Finally, (3) SPARTA will investigate the non-perturbative nature of double-copy and explore its role as a new S-matrix principle. SPARTA will reach these goals thanks to an original approach to non-perturbative unitarity, "scattering-from-production", which tackles the bottlenecks of the non-perturbative approach, while making use of modern perturbation theory, and using powerful numerical tools. By this unique approach, SPARTA will lay the foundations of a grand programme, at the interface of scattering amplitudes and non-perturbative S-matrix.

A more general theory than the Standard Model (SM) of Particle Physics should exist to describe various phenomena unexplained in SM. Direct searches for New Physics (NP) have been unsuccessful until now. The project VBStime propose to indirectly probe NP through the study of vector boson scattering, which is a process particularly sensitive to NP and that is for now almost unexplored due to its experimental difficulty. The observation potential of VBS states will grow only slowly accumulating luminosity. Therefore, strong progresses in VBS field will only be made possible by the development of novel data analysis techniques. VBStime proposes to create such techniques via synergies with cutting-edge Machine Learning (ML) and data mining technologies, and to apply them to current and future LHC data. The three objectives of the projet are to get a better knowledge of the vector boson scattering process using data collected by the ATLAS detector in Run 2 and Run3 periods of LHC exploitation (2015-2018 and 2021-2022), create a synergy between ML and high-energy physics community to improve sensitivity in all steps of the project, and interpret the results in term of new-physics presence, in a model-independent and indirect way. For this, the present team need to be complemented by more computing-science oriented profiles.

Non-thermal emission represents a crucial tool in the comprehension of the high-energy sky. Yet, mysterious excesses exist. Among them, the Fermi GeV excess and the 511 keV line emission still lack a definitive explanation and might thus point towards new sources and/or emission mechanisms. I plan to conclusively test the hypothesis that these two emissions arise from faint point-source populations, linked to binary systems in the Galactic bulge, with a new multi-wavelength analysis. I will use gravitational wave signatures as further leverage in the modelling of Galactic binaries, and thus probe the synergy of the high-energy sky with this new observational window for the first time. My research will also sharpen our diagnostic capabilities on dark matter and boost the discovery potential of future searches building on the new techniques developed. The characterisation of point-source populations in the bulge will be a leap forward in high-energy astrophysics and Galactic astronomy.

Radiative decays of B hadrons are flavour changing neutral currents (FCNC) proceeding at quark level through a b→qγ transition (q=s,d). Alike semileptonic decays (b→ql+l- where l=e,μ,τ), they are only allowed at loop-level in the Standard Model (SM) which originally made them an excellent probe for tree-level new physics contributions. FCNCs were observed at Tevatron and B-factories with properties compatible with SM values. From then on, they are serving precision tests at LHC experiments, and notably at LHCb. Another side of the physics reach of radiative decays is the determination of the quark mixing parameters, encoded in the Cabbibo-Kobayashi-Maskawa (CKM) matrix. Together with other experimental observables, radiative data can improve the constraints on the small set of independent matrix parameters, in particular through a determination of the |Vtd/Vts| ratio. CKM metrology therefore performs powerful consistency tests of the quark sector of the SM. A key observable in radiative decays is the polarisation of the emitted photon. Indeed, the chirality of the weak interaction dictates that the rate of b→qγ transitions is dominated by a left-handed amplitude while the right-handed amplitude is suppressed by the ratio of quark masses mq/mb. Departure from this prediction would be a clear signal for new physics. Several methods to indirectly measure the photon polarisation were proposed, each posing specific experimental and theoretical challenges. The method of AGS oscillations [1] exploits the time-dependent asymmetry in B and B radiative decays. Thanks to a cancellation of QCD uncertainties, the SM prediction for the asymmetry is quite precise. Furthermore, the method applies to several exclusive Bd and Bs decay modes provided their final state is an eigenstate of CP symmetry, allowing for independent tests and a powerful combination of the results. This project aims to maximise the sensitivity of the current and future LHCb datasets to new physics effects through AGS oscillations. This should be achieved by first considering the full inclusive mass spectrum of final-state hadrons (rather than the mass region where only one resonance dominates) thanks to a better control of the increased backgrounds and a time-dependent amplitude analysis of the Dalitz plot; and secondly by considering several experimentally accessible Bd and Bs decay modes and combining the CP measurements in each of them. A second side of the project is the determination of the |Vtd/Vts| CKM ratio using Cabibbo-favoured b→sγ and Cabibbo-suppressed b→dγ transitions. While this was done at B-factories with Bd decays only, LHCb should be able to also propose a measurement in Bs decays (for which no sensitivity is reported in the Belle2 physics book). Given the backgrounds, the mass resolution in that last case is crucial and this measurement necessarily relies on samples of photons reconstructed as e+e- pairs rather than standalone calorimeter clusters. The low reconstruction efficiency for such photons (converting into the detector material) makes the measurement of the Bs suppressed decay very challenging, even when the Run3 dataset will be made available. It is thus proposed to improve the algorithm itself and deploy it as soon as possible during Run3. [1] D. Atwood, M. Gronau and A. Soni, arXiv:hep-ph/9704272

DIRECTA (Deep learnIng in REal time for the Cherenkov Telescope Array), as the name states, is a project to apply deep learning solutions based on convolutional neural networks (CNNs) to the Cherenkov Telescope Array (CTA), in real-time. It is a continuation of the GammaLearn project, that already demonstrated the applicability of CNNs to CTA data, and of the ACADA work package that is developing the real-time analysis for CTA using the standard reconstruction techniques. Its objective is the demonstration of the applicability of CNNs in real-time for CTA with a working proof-of-concept applied to the already observing Large-Sized Telescope 1 (LST-1) and later to the LST-2 and Mid-Sized Telescope 1 whose construction will start in 2023. It will greatly improve CTA's reconstruction performances in real-time necessary for the study of transient sources such as gamma-ray bursts and flaring active galactic nuclei, of the Lorentz Invariance Violation and of the Extragalactic Background Light.