# Théorie

# TBA

# AdS_2 holography - Mind the Gap!

Black holes appear to lead to information loss, thus violating one of the fundamental tenets of Quantum Mechanics. Recent Information-Theory-based arguments imply that information loss can only be avoided if at the scale of the black hole horizon there exists a structure (commonly called fuzzball or firewall) that allows information to escape. I will discuss the highly-unusual properties that this structure must have and how these properties emerge in the realization of this structure in String Theory via branes, fluxes and topology.

# The Universe as a Quantum Lab

The early Universe offers exciting possibilities to test the quantum theory in a different regime than the one probed in conventional labs, and learn more about its foundations, applicability, relation to gravity, and potential limits.

# Bayesian measurements of inflation with additional fields

In this talk I will demonstrate how, by introducing additional scalar degrees of freedom, one can measure properties of the inflationary era which may be otherwise inaccessible. Using two explicit examples (the curvaton and a feebly interacting model of dark matter), which introduce new informative priors into the post-inflationary phenomenology, we are able to constrain either the total duration that inflation takes place or its energy scale independently of the tensor-to-scalar ratio.

# Inflation beyond GR

Scalar-tensor theories of gravity have become a very rich framework from which one can construct viable phenomenological models of early- and late-time cosmology. In particular for inflation, previous models constructed using the Horndeski Lagrangian give predictions which are now in tension with CMB data. On the other hand, by trying to fit the observations, one would find instabilities at the level of the quantum perturbations. Furthermore, computing the standard inflationary observables in a semi-analytical way is a nontrivial task.

# The `unitarity problem' of Higgs inflation in the light of collapse dynamics

Higgs Inflation is no doubt one of the most favoured models of inflation in present time. But the huge non-minimal coupling of the Higgs field with gravity required for the model to work often raises concern which is dubbed as the 'unitarity problem' of Higgs inflation. We will show that CSL-like collapse dynamics, otherwise applied to inflationary dynamics in order to explain the quantum-to-classical transition of primordial quantum modes, can bring down the value of non-minimal coupling considerably.

# CFT Entanglement Entropy and Topological Terms in Gravity

In 2006, Ryu and Takayanagi provided a general recipe on how to compute

entanglement entropy of a Conformal Field Theory using gauge/gravity

duality. This holographic prescription, which considers the extension of

the entangling region from the boundary into an Einstein space bulk, has

produced remarkable insight on general properties of strongly correlated

systems. However, this progress has been made on a rather case-by-case

basis, as it requires proper renormalization of the gravity action in

the bulk.

# Observational constraints on inflationary potentials within the quantum collapse framework

The inflationary paradigm is the most successful model for the

generation of primordial perturbations. These perturbations have a

purely quantum origin, while the inhomogeneities and anisotropies

observed today exhibit a classical behavior. The model called Continuous

Spontaneous Localization (CSL) is a proposed mechanism to solve the

measurement problem in quantum mechanics. In this presentation, we will

analyze the theoretical predictions resulting from incorporating the CSL

# Extended Cuscuton: Formulation and Cosmology

Among single-field scalar-tensor theories, there is a special class called "cuscuton,"

which is represented as general relativity with a noncanonical scalar field. This theory

has a remarkable feature that scalar perturbations do not propagate on a cosmological

background. We specify a subclass of the (beyond) Horndeski class having this

property and thus extend the framework of cuscuton. We also discuss the stability of

cosmological perturbations in the extended cuscuton models.