Centre de Physique Théorique


Mars 2023

Vendredi 3 mars 14:00-15:00, BU, 0th floor

Cosmology and new physics

Giovanni Cabass (IAS, Princeton)

I review the two main observables that make cosmology one of the main avenues for discovering physics beyond the Standard Model : primordial Gravitational Waves and Large-Scale Structure. Primordial gravitational waves are quantum fluctuations of the metric during the epoch of cosmological inflation and source a peculiar pattern of polarization of the Cosmic Microwave Background, the so-called B modes. LSS observations, instead, probe the structure of the universe on its largest scales by looking at the clustering of galaxies. I discuss how B-mode experiments targeted at measuring primordial Gravitational Waves probe frequencies unaccessible to Earth- and space-based interferometers. They will allow us to answer fundamental questions about inflation, e.g. what was its energy scale, and to distinguish between different models for the potential of the inflaton field that drives the epoch of accelerated expansion. I show how recent developments in the "Cosmological Bootstrap" program have been instrumental in understanding the properties of primordial Gravitational Waves, more precisely their interactions and resulting primordial non-Gaussianity. I then discuss how the modern techniques of the Effective Field Theory of Large-Scale Structure are fundamental in discovering new light degrees of freedom and interactions in the dark sector, learning the composition and properties of dark matter, and constraining modified gravity. I conclude by showing how these techniques applied to the analysis of data from the BOSS galaxy survey allow to learn about the properties (mass, spin, speed of propagation) of light degrees of freedom during inflation.

Vendredi 10 mars 14:00-15:00, BU, 0th floor

Open EFTs : How can we access the quantum information properties of inflationary models ?

Thomas Colas

Despite being created through a fundamentally quantum-mechanical process, cosmological structures have not yet revealed any sign of genuine quantum correlations. Among the obstructions to the direct detection of quantum signatures in cosmology, environmental-induced decoherence is arguably one of the most inevitable. If we want to assess decoherence in cosmology, we need to evaluate the quantum information properties of inflationary models. In this talk, I will present the Open Effective Field Theory program and exhibit situations where the dynamics of cosmological inhomogeneities evade what was known so far in the lab.

Vendredi 10 mars 15:00-16:00, BU salle de séminaires

Modeling Single Cell and Multicellular Systems using the Phase Field Method

Marcos Gouveia, Center for Physics of the University of Coimbra

Abstract :

In the past two decades, the phase field method has been a tool used in mathematical models of biological systems. Its ability to describe systems with complex geometries, using a diffuse interface, avoids the problem of interface tracking and simplifies the boundary conditions in irregularly shaped domains.

We present a single cell model for the dynamics of keratin in the cytoskeleton, where we intend to understand how the spatial distribution of the filament network is affected when the cell expresses mutant keratin. To further understand how the amount of mutated keratin in the cell influences the formation of keratin aggregates and the filament network disruption, we propose that an asymmetric binding of wild-type and mutant keratin is in the genesis of these keratin aggregates.

Furthermore, we show how the phase field method can be coupled to elasticity theory, in order to describe how the mechanical properties of the extracellular matrix can influence endothelial cell migration during the formation of new blood vessels. Our results show that the length of the resulting vessels do not depend linearly on the stiffness of the ECM, and there is an optimal value of rigidity for which cell migration is maximized.

Finally, we present a multi-phase field model to describe a vessel with a tubular structure where each individual cell and the interactions with its vicinity are described using a set of order parameters, one for each cell. We show that endothelial cell polarization is essential to obtain a vessel structure where cell shape is close to what is observed experimentally. We also simulate a sprouting event and observe how the velocity of the cell that leads the formation of the sprout, as well as the proliferative activity of its neighboring cells affects the newly formed vessel structure.

Lundi 13 mars 14:00-15:00, BU

Hadrons, Superconductor Vortices, and Cosmological Constant

Keh-Fei Liu (U. of Kentucky)

We point out that there is an energy-equilibrium correspondence from the gravitational form factors (GFF) of hadrons which reveals that the trace anomaly, emerging from the glue condensate in the vacuum, gives a negative constant pressure which leads to confinement, much like the confinement mechanism for the vortices in type II superconductors. Both the trace anomaly and the cosmological constant in Einstein’s equation for the static Universe are in the metric term of the energy-momentum tensor. Their similarities and differences are discussed. Finally, a lattice calculation of the trace anomaly distribution in the pion resolves a pion mass puzzle and provides a definite evidence that the conformal symmetry breaking and chiral symmetry breaking in QCD are intertwined.

Vendredi 17 mars 14:00-15:00, BU, 0th floor

A symplectic perspective on gauge symmetries, corners, soft charges, memory, and superselection

Aldo Riello

Next year, it will be 50 years since Marsden and Weinstein’s seminal paper on symplectic reduction. Perhaps surprisingly, this classic tool is all the more relevant today, when the interest of theoretical and mathematical physicists shifted towards higher codimensions. In this seminar I will review my recent work on the foundations of a theory of symplectic reduction for gauge theories on a manifold with boundaries and corners, which has numerous physical consequences for our understanding of soft charges and “electric flux superselection” at a null boundary. This work also provides a new perspective on the well-known and widely-used Ashtekar-Streubel phase space.

Vendredi 24 mars 14:00-15:00, BU, 0th floor


Roberto Oliveri

Vendredi 31 mars 14:00-15:00, BU, 0th floor

Corner Symmetries in Gravity

Luca Ciambelli