Physics

In this talk I will introduce the Fully Constrained Formulation (FCF) of General Relativity. In this formulation one has a hyperbolic sector and an elliptic one. The constraint equations are solved in each time step and are encoded in the elliptic sector; this set of equations have to be solved to compute initial data even if a free evolution scheme is used for a posterior dynamical evolution. Other formulations (like the XCTS formulation) share a similar elliptic sector. I will comment about the local uniqueness issue of the elliptic sector in the FCF. I will also described briefly the hyperbolic sector. I will finish with some recent reformulation of the equations which keeps the good properties of the local uniqueness, improves the numerical accuracy of the system and gives some additional information.

The Event Horizon Telescope is a global effort to construct an
Earth-sized virtual radio telescope array, with the goal to make pictures and
movies of two nearby supermassive black holes. A detailed theoretical
understanding of black hole accretion is now crucial to interpret these
observations. I will review our current efforts to model polarimetric
properties of light produced in synchrotron processes in plasma falling
towards the event horizon. The numerical models are based on general
relativistic magnetohydrodynamics simulations so they are capable of capturing
the complex dynamics of magnetic fields and their interactions with plasma. It is now
important to understand the polarized radiative transfer in these simulations
to correctly predict the observational signatures of the events at the event
horizon scales where the accretion disk and jet are connected.

In string compactifications the roles of physics and geometry are intrinsically intertwined. While the goals of these 4-dimensional effective theories are physical, the path to those answers frequently leads to cutting-edge challenges in modern mathematics. In this talk, I will describe recent progress in characterizing the geometry of Calabi-Yau manifolds in terms their description as elliptic fibrations. This description has remarkable consequences for the form of the string vacuum space and the properties of string effective theories, including particle masses and couplings.

The Cryogenic Underground Observatory for Rare Events (CUORE), hosted at the Laboratori Nazionali del Gran Sasso in Italy, is the first tonne-scale cryogenic experiment searching for neutrinoless double-beta decay (0nuDBD) of 130Te. The observation of this process would prove that lepton number is not a symmetry of nature and that neutrinos are Majorana particles. CUORE, started in 2017, is currently in stable data taking: a raw exposure of ~ 1 tonne yr has recently been achieved. In this talk, the most recent results of CUORE for the 0nuDBD channel as well as for other physical processes of interest (2nuDBD, decays to excited states,..) will be presented, together with a review of the detector features and performance.

A vibrant program has formed in recent years in various scientific disciplines to take advantage of near-term and future quantum-simulation and quantum-computing hardware to study complex quantum many-body systems, building upon the vision of Richard Feynman for quantum simulation. Such activities have recently started in nuclear and particle physics, hoping to bring new and powerful experimental and computational tools to eventually address a range of challenging problems in strongly interacting quantum field theories and nuclear many-body systems. In this talk, I review a number of important developments, including proposals for simulating strongly interacting field theories with the ultimate goal of studying strong dynamics of quarks and gluons, and of nucleons. Some of the requirements for hardware technologies that are expected to enable both the analog simulations and the digital quantum computations of these problems will be enumerated, and an experiment-theory co-development program will be motivated with an emphasis on trapped-ion platforms.

The DAMIC experiment exploits the exceptional energy and spatial resolution of charge coupled devices (CCDs) to search for dark matter particles. We present the latest results from the 11 kg-day
exposure collected with the DAMIC detector at SNOLAB. We build on previous analyses to distinguish between bulk and surface backgrounds to construct a robust radioactive background model down to energies as low as 50 eV. We compare the observed spectrum of events to the background-model prediction to search for an excess bulk signal, as would be expected from dark matter.

The EDELWEISS direct detection experiment uses cryogenic Ge semiconductor detectors to search for sub-GeV dark matter (DM) particles. With its low gap energy, germanium is an excellent target to explore DM particles interactions with nucleons in the sub-GeV range, and DM-electron interactions in the MeV range, as well as search for the absorption of eV-scale dark photons. The collaboration has recently obtained the first Ge-based constraints on sub-MeV dark DM particles interacting with electrons using a 33.4 g Ge cryogenic detector prototype with a 0.53 electron-hole pair (rms) resolution, operated underground at the Laboratoire Souterrain de Modane.
These results will be presented, as well as the EDELWEISS-SubGeV plans to achieve lower threshold and more efficient particle identification at low energy.

A dark matter candidate lighter than about 30 eV exhibits wave behavior in a typical galactic environment. Examples include the QCD axion as well as other axion-like-particles. We review the particle physics motivations, and discuss experimental and observational implications of the wave dynamics, including interference substructures, vortices, soliton condensation and black hole hair.

Gravitational waves provide a unique way to study the universe. From the initial direct detection of coalescing black holes in 2015, to the ground-breaking multimessenger observations of coalescing neutron stars in 2017, and continuing with the now routine detection of merging stellar remnants, gravitational wave astronomy has quickly matured into a key aspect of modern physics. After briefly discussing what we've begun to learn from the new gravitational-wave transient catalog published by the LIGO, Virgo, and KAGRA collaborations (GWTC-2), I will discuss novel tests of fundamental physics GWs enable. In particular, I will focus on our current understanding of matter effects during the inspiral of compact binaries and matter at supranuclear densities, including possible phase transitions, through tests of neutron star structure. Detailed knowledge of dynamical interactions between coalescing stars, observations of extreme relativistic astrophysical systems, terrestrial experiments, and nuclear theory provide complementary views of fundamental physics. I will show how combining aspects from all these will improve our understanding of dense matter through the example of how we can determine whether newly observed objects are neutron stars or black holes.

Neutrino oscillations have been probed during the last few decades using multiple neutrino sources and experimental set-ups. In recent years, very large volume neutrino telescopes have started contributing to the field. These large and sparsely instrumented detectors observe atmospheric neutrinos for combinations of baselines and energies inaccessible to other experiments. IceCube, the largest neutrino telescope in operation, has used this to measure standard oscillations and place limits on exotic proposals, such as sterile neutrinos. In this talk, I will go over the newest results from IceCube as well as the improvements expected thanks to a new detector upgrade to be deployed in the near future.

A standard account of the measurement chain in quantum mechanics involves a probe (itself a quantum system) coupled temporarily to the system of interest. Once the coupling is removed, the probe is measured and the results are interpreted as the measurement of a system observable. Measurement schemes of this type have been studied extensively in Quantum Measurement Theory, but they are rarely discussed in the context of quantum fields and still less on curved spacetimes. 

In this talk I will describe how measurement schemes may be formulated for quantum fields on curved spacetime within the general setting of algebraic QFT. This allows the discussion of the localisation and properties of the system observable induced by a probe measurement, and the way in which a system state can be updated thereafter. The framework is local and fully covariant, allowing the consistent description of measurements made in spacelike separated regions. Furthermore, specific models can be given in which the framework may be exemplified by concrete calculations.

I will also explain how this framework can shed light on an old problem due to Sorkin concerning "impossible measurements" in which measurement apparently conflicts with causality.

The talk is based on work with Rainer Verch [Leipzig], (Comm. Math. Phys. 378, 851–889(2020), arXiv:1810.06512; see also arXiv:1904.06944 for a summary) and a recent preprint arXiv:2003.04660 with Henning Bostelmann and Maximilian H. Ruep [York].