Symmetries are fundamental to our understanding of nature. In Quantum Field Theory, they have become the guidelines for the formulation of fundamental theories. In this talk, I will go into the importance of symmetries and the concept of spontaneous symmetry breaking to understand the early Universe. Then, I will discuss gauge symmetries and their fundamental differences with physical symmetries, and the subsequent contradiction in our understanding of the Higgs mechanism as a spontaneously broken gauge symmetry. I will discuss alternative understandings of the Higgs mechanism and the importance of gauge symmetries despite their seemingly redundant nature.
Quantization of general relativity in four dimensions is not straightforward because Newton's constant carries units of (length)^2 which means the theory is non-renormalizable. Up to now, the only quantum-mechanical approach which has allowed the perturbative computation of graviton scattering at all energy scales is superstring theory. Although it might be a long time before experimental tests of quantum gravity will be able to tell us if superstring theory correctly describes our universe, the theory has other interesting properties such as supersymmetry and duality symmetry whose study has been useful for several branches of physics and mathematics.
Foraging is a ubiquitous behavior performed by all animals and human beings as they search for food needed to survive. Foraging theory has been key to understanding a variety of model systems but it still lacks mechanistic insights that relate it to neurobiological and other physiological mechanisms. In this talk, I will present work that aims to develop a quantitative mechanistic framework of foraging with a specific focus on patch foraging either of an individual agent or in a social context. I will also present a learning model that accounts for how agents learn the structure of the environment
The Cosmic Microwave Background (CMB) is the most distant light that we can observe today. Since its emission roughly 380.000 years after the Big Bang it crossed all the Universe while coming to us. During their travel, the photons of the CMB have been deflected by the matter they encountered along their path, an effect called gravitational lensing. This deflection of the CMB is a powerful observable, proportional to the integral of the matter distribution up to the early Universe. I will introduce how we can reconstruct this deflection from observations of the CMB. I will then demonstrate how CMB lensing can put tight constraints on the content of the Universe, on the sum of the neutrino masses, and help us discover cosmic inflation. Lastly, I will introduce a new CMB lensing estimator, which will reconstruct optimally the lensing field for the next generation of CMB surveys.
Addressing Quantum Chromodynamics (QCD) in the infrared is a notoriously difficult task due to the size of the interaction strength. This has instigated the development of non-perturbative approaches based either on the lattice discretization and the statistical evaluation of the QCD functional integral or on its continuum reformulation in terms of infinite hierarchies of equations. Lattice QCD provides an almost exact description of QCD that can however not be used in all situations. As for continuum approaches, even though they can be extended to these situations in principle, they very often rely on uncontrolled truncations that prevent a quantitative estimate of the error.Over the last decades, the lattice simulation of Euclidean QCD correlators in the Landau gauge has revealed unexpected features that shed some light on how the various QCD fields are coupled in the infrared. This allows one to contemplate a "third way" into infrared QCD. In this talk, I review a ten-year effort to put these ideas into solid ground, using the Curci-Ferrari action, a one-parameter model for Landau gauge-fixed QCD in the infrared. In particular, I will discuss how this approach allows one to retrieve the lattice results for the QCD correlation functions and to investigate features of the phase structure that relate to the most fundamental properties of QCD such as confinement or chiral symmetry breaking.
