Line-intensity mapping, dark matter, and dark energy

I will review line-intensity mapping, a new and rapidly evolving avenue to study large-scale structure. I will then discuss some applications to cosmology, the search for dark matter, and the study of dark energy and the Hubble tension.

Friday, 16 July 2021, ore 14:30 — Zoom seminar

B-physics anomalies and the flavor problem

Recent data in B-meson decays indicate a coherent pattern of deviations from the Standard Model predictions. I critically review these data and discuss their interpretation. I will discuss, in particular, how present data points toward new dynamics not far from the TeV scale, possibly by linked to the origin of the mass hierarchies observed in the Standard Model spectrum. Implications for future measurements both at low and high-energies are also briefly discussed.

Friday, 18 June 2021, ore 14:30 — Zoom seminar

Wormholes and the information paradox

Black hole evaporation seems to create too much entropy, violating unitarity. This is the essence of Hawking's black hole information paradox. I will describe recent progress on this problem involving spacetime wormholes in the gravitational path integral. This leads to a new result for the entropy of Hawking radiation that is compatible with unitarity, and has general consequences for how we interpret black holes in quantum gravity. It also leaves many open questions that I will highlight in this talk.

Friday, 28 May 2021, ore 14:30 — Zoom seminar

The Modern Amplitudes Program: Supercolliders, Fluid Dynamics, and Black Holes

Scattering amplitudes are fundamental observables encoding the dynamics of interacting particles. In this talk I describe how to systematically construct these objects without reference to a Lagrangian. The physics of real-world particles like gravitons, gluons, and pions are thus derived from the properties of amplitudes rather than vice versa. Remarkably, the expressions gleaned from this line of attack are marvelously simple, revealing new structures long hidden in plain sight. In particular, I describe how gravity serves as the "mother of all theories" whose amplitudes secretly unify, among others, all gluon and pion amplitudes. This fact has far-reaching theoretical and phenomenological connections, e.g. to fluid mechanics and to new approaches to the black hole binary inspiral problem.

Friday, 8 May 2021, ore 17:00 — Zoom seminar

Quantum Simulation of Abelian and non-Abelian Gauge Theories

Besides lattice QCD in particle physics, strongly coupled gauge theories arise, for example, in the condensed matter physics of spin liquids, or in the quantum information theory of Kitaev's toric code, which is a Z(2) lattice gauge theory. Numerical simulations of gauge theories on classical computers, in particular, at high fermion density or in out-of-equilibrium situations, suffer from severe sign problems that prevent the importance sampling underlying Monte Carlo calculations. Quantum simulators are accurately controllable quantum devices that mimic other quantum systems. They do not suffer from sign problems, because their hardware is intrinsically quantum mechanical. Recently, trapped ions, following a laser-driven stroboscopic discrete time evolution through a sequence of quantum gate operations, have been used as a digital quantum simulator for particle-anti-particle pair creation in the Schwinger model. Analog quantum simulators, on the other hand, follow the continuous time-evolution of a tunable model Hamiltonian. Using ultra-cold atoms in optical lattices, analog quantum simulators have been designed for Abelian and non-Abelian lattice gauge theories. Their experimental realization is a challenge for the foreseeable future, which holds the promise to access the real-time dynamics of string breaking, the out-of-equilibrium decay of a false vacuum, or the evolution of a chiral condensate after a quench, from first principles. Quantum link models which realize gauge theories including QCD not with classical fields but with discrete quantum degrees of freedom, are ideally suited for implementation in quantum matter. For example, alkaline-earth atoms, whose nuclear spin represents an SU(N) degree of freedom, naturally embody fermionic rishon constituents of gluons. CP(N-1) models, which are toy models for QCD, can be quantum simulated in a similar way via SU(N) quantum spin ladders.

Friday, 16 April 2021, ore 14:30 — Zoom seminar

Understanding the Higgs mass in string theory

Almost all existing calculations that concern the Higgs mass are performed within the framework of an effective field theory. While sufficient for certain purposes, such calculations throw up problems to do with fine-tuning and naturalness in particular the famous hierarchy problem. This makes attempts within field theory to understand the Higgs mass futile. Even calculations done within string theory fail to respect the full string symmetries that are responsible for many of the remarkable finiteness properties for which string theory is famous. Chief among these symmetries is worldsheet modular invariance, which is an exact symmetry of all perturturbative closed-string vacua. And yet if the UV is tamed by this symmetry then it should be exact even today. In this talk I discuss what can be learned from a fully consistent treatment within a modular invariant theory. Using our framework, I describe how a gravitational modular anomaly generically relates the Higgs mass to the one-loop cosmological constant, thereby yielding a string-theoretic connection between the two fundamental quantities which are known to suffer from hierarchy problems in the absence of spacetime supersymmetry. I also discuss a number of critical issues involving the use and interpretation of regulators in UV/IR-mixed theories such as string theory. Finally, I show how the Higgs mass in closed string theories can be recast as a supertrace over only those string states which are physical (i.e., level-matched), thereby al- lowing us to identify a generic “stringy” Coleman-Weinberg potential for the Higgs fields in such theories.

Friday, 12 March 2021, ore 14:30 — Zoom seminar

Cosmology with Gravitational Waves

Gravitational Waves (GWs) will become the most powerful tool to explore our Universe from its early epoch until nowadays. The LIGO-Virgo detection of several GW signals has greatly boosted the astrophysical understanding of compact objects, and, at the same time, has given strong constraints on modified-gravity models. The upcoming surge of GW detections by future space-based (LISA, DECIGO, BBO) and ground-based (ET, Cosmic Explorer, LIGO India) will clearly promote GWs at the same level of the Cosmic Microwave Background (CMB) and Large Scale Structures (LSS) as a tracer to study our Universe. Therefore the detection of GWs propagating through cosmic structures can provide invaluable information on the geometry and content of our Universe. After a brief introduction of the properties of GWs, I will investigate the effect of including perturbations in the estimate of luminosity distances as inferred from gravitational wave observations. Then I will discuss tools and techniques to characterise the Stochastic Gravitational Wave Background (SGWB), both of cosmological (e.g inflation, phase transition) and astrophysical origin that might be detected by next generation ground and space-based interferometers.

Friday, 26 February 2021, ore 14:30 — Zoom seminar

Muon Colliders: a challenging opportunity

A multi-TeV muon collider is a discovery machine and an invaluable tool for many precision measurements such as the shape of the Higgs boson potential. The update of the European Strategy for Particle Physics recognized the unique opportunity of a muon collider to reach the energy frontier, despite the challenges to produce intense cooled muon beams. A 3 TeV and a 10+ TeV collider option is the main focus of the forming international collaboration, strengthen and revived during the ongoing US Snowmass process. The Design Study will identify the key issues and risks, the R&D priority plan and will provide a baseline concept for a muon collider facility (machine, experiment and machine detector interface) with well-supported performance expectations to ensure the overwhelming scientific merits. The status of the project, future plans and synergies will be discussed.

Friday, 29 January 2021, ore 14:30 — Zoom seminar

Accidental Dark Matter

The Standard Model of Particle Physics gives an extremely accurate and successful description of all the experiments performed in laboratories, but it fails to reproduce some of the most fundamental properties of our Universe and its cosmological evolution. The abundance of Dark Matter is one of them. In this talk I will review the idea that Dark Matter is in the form of a particle whose stability is the consequence of an accidental symmetry. Accidental stability is already realized in Nature by the proton, whose stability follows from baryon number conservation. I will discuss the implications of the Accidental Dark Matter paradigm and analyze some of the theories that have been proposed to realize it.

Friday, 11 December 2020, ore 14:30 — Webex seminar

Temperature dependence of the axion mass: a case for master-field simulations

The axion is a hypothetical particle associated with the resolution of the so-called strong CP problem through the Peccei-Quinn mechanism. As dark-matter candidate, the axion is a rather special case in view of the fact that its mass is generated by the chiral anomaly in QCD and thus rapidly goes to zero at high temperatures.

The effect is an entirely non-perturbative one, which can, in principle, be studied quantitatively in lattice QCD. In this talk, the difficulties met in such computations are briefly exposed and it is shown that they can be overcome using master-field simulations. A sample computation is then presented, confirming the feasibility of such simulations and the rapid decay of the axion mass at temperatures above the deconfinement temperature.

Friday, 20 November 2020, ore 14:30 — Webex seminar