# Théorie

# 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.

# TBA

# 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.

# Stochastic inflation in a general field space

Inflationary models in non-trivial field spaces encoded by their non-canonical kinetic terms have attracted attentions recently. We have then extended the so-called stochastic formalism to such a general case. This formalism investigates the fluctuation of inflatons treating them as Brownian motions. This work highlights the involved problem of this formalism, related with the mathematical uncertainty of the definition of noise integral. Comparing the correlation functions in the stochastic formalism and quantum field theory, we clarify that this uncertainty cannot be rem

# The Matter-Gravity Entanglement Hypothesis

I discuss my `matter-gravity entanglement hypothesis' which,

amongst other things, offers a solution to the black-hole information

loss puzzle.

Reference: B.S. Kay, The matter-gravity entanglement hypothesis,

Foundations of Physics (available online at 10.1007/s10701-018-0150-7

[8]) [arXiv:1802.03635]

# Constructing degenerate higher-order theories

Scalar-tensor theories serve models for inflation and dark energy. Many efforts have been made recently for constructing the most general scalar-tensor theories with higher-order derivatives in their Lagrangian. Since higher-derivative theories are typically associated with Ostrogradsky ghost which causes unbounded Hamiltonian, it is important to clarify how to evade it.

# Perturbative dynamics of massive gluons

Lattice simulations of Yang-Mills theories and QCD in the Landau gauge have

demonstrated that the gluon propagator saturates at vanishing momentum. This can

be modeled by a massive deformation of the corresponding Faddeev-Popov

Lagrangian known as the Curci-Ferrari model. The latter does not modify the known

ultraviolet regime of the theory and provides a successful perturbative description of

essential aspects of the non-Abelian dynamics in the infrared regime, where, in

# Fermion masses, quark mixing and Flavor Changing Neutral Currents from a gauged SU(3)_F family symmetry

Within a broken local gauge vector-like $SU(3)_F$ family symmetry, we address the problem of quark masses and mixing, and study some rare flavor violating processes induced by the new gauge bosons, which can generate transitions between different families and so introduce "Flavor Changing Neutral Currents"(FCNC) couplings at tree level. We find out that some of the most dangerous FCNC processes, like for instance;