Large efforts have been made in the past decades to develop new types of cryogenic sensors for various applications, ranging from material analysis for the industry to astroparticles detection. Future spatial programs involve detectors working around 50 mK, while their readout electronics (eg preamplifiers), still working at much higher temperature, frequently prevent extracting the best performance from these detectors. In this wide and competitive context, mesoscopic devices provide attractive solutions for these problems. In this project, we propose to implement a mesoscopic charge amplifier for the readout of ionisation detectors, used for particles detection in many domains. Importantly, our device could improve by an order of magnitude the detection threshold of the EDELWEISS experiment for dark matter search, to which the CSNSM participates. The course of this research will go through developments, both fundamental and instrumental, based on the mesoscopic physics of quantum superconducting circuits. The aim of the present application is to provide with the funds necessary to initiate this new activity, consecutive to the hiring of the project's principal investigator at the CNRS (CSNSM). This project takes place within a broader framework aimed at developing a front-end mesoscopic cryoelectronics, to catch up with the latest developments in cryogenic detectors.

Smith-Purcell radiation offers the possibility to measure components similar to the Fourier transform of the longitudinal profile of ultra-short electron bunches. This information can be used to reconstruct the actual longitudinal profile of electron bunches. The measurement of such profile will be critical in the development of new particle accelerators such as drivers for Free Electron Lasers or plasma-wakefield accelerators. Indeed, at the latest conference, the community received our recent results with strong interest. Building on our recent results, we propose to perform a systematic experimental study of Smith-Purcell radiation to validate theoretical predictions and numerical simulations in a real accelerator environment. These experimental studies will allow us to build a well understood Smith-Purcell radiation monitor to measure components in wavelengths of the longitudinal profile of ultra-short electron bunches. Another task will focus on converting these components in a reconstruction of the actual longitudinal profile. To maximize our chances of success we will proceed by steps from the easiest to the most difficult environment where to perform such measurement. We will start by a systematic study at the end of the SOLEIL LINAC where we will easily get access to a large number of electron pulses. Theses pulses will be several picoseconds long and therefore the Smith-Purcell radiation expected from these pulses will be in a wavelength range (millimetric waves) where “optical” components can be built rather easily in a mechanical workshop such as the one available at LAL. The results of this study will allow us to build a single shot longitudinal profile monitor for these electron bunches in the picosecond range that will be tested at the same location. This will be followed by a study at SPARC in Frascati (Italy) where we will have access to shorter pulses (and a tuneable length). The tests at SPARC will allow us to study in depth Smith-Purcell radiation in the hundreds femtoseconds range, leading to the construction of a single shot profile monitor suitable for that pulse length range. In parallel we will continue tests on FACET at SLAC (USA). These tests which have already started will allow us to explore the low hundreds femtoseconds pulse length range and at a much higher energy. Theses tests together with the knowledge accumulated at SPARC and SOLEIL will allow us to build a single shot profile monitor suitable for FACET. Gathering all our experience from the tests at SOLEIL, SPARC and FACET we will be able to move to the much more challenging environment of laser-driven plasma wakefield accelerators. There we will build a single shot longitudinal profile monitor to achieve our ultimate goal of measuring the longitudinal profile of the electron pulses produced by a laser-driven plasma accelerator. Unlike previous measurements performed on conventional accelerators, this measurement will have to deal with large variation from shot to shot and this is where the single shot nature of the monitor will be critical. It is important to stress that such longitudinal measurement in a single shot has never been attempted at a laser-driven plasma-wakefield accelerator. It will therefore provide a new observable dimension in the study of the performances of these accelerators. Over the course of the project we will have used an easy range of wavelength to build firm foundations for this monitor and then moved by steps to more difficult wavelength ranges and settings to make very challenging measurements. The main deliverable will be a single shot longitudinal profile monitor for plasma-wakefield accelerators but as by-products we will also have produced designs of monitors interesting our partners at SOLEIL (for LUNEX5) and SPARC (for their FEL driver and their plasma accelerator) and we will have established an internationally recognised group at LAL working on diagnostics for plasma accelerators.

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.

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.

GW170817, the first detection of gravitational waves (GWs) from a binary neutron star merger together with its electromagnetic counterpart has proven the immense potential of this multi-messenger astronomy for our understanding of the nature of gravity and the properties of dense matter. We propose here to advance on the latter, addressing the following questions: To which extent can current and future GW observations constrain the underlying microphysics, specifically the equation of state and neutrino interaction rates? Can a potential phase transition be detected? To answer these questions we will study as well the remnant of binary neutron star mergers as proto-neutron stars, the compact postbounce objects in a core-collapse supernova with a new fast and flexible numerical tool. We shall largely explore the microphysics model's parameter space and simulate the possible imprints on GW emission from these objects. In view of the difficult GW data analysis, this work will be crucial to fully exploit the science of upcoming GW data.