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

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; 

Galileon p-form theories

I will discuss the generalization to p-forms of the Galileon idea: to
construct the most general theory of an (abelian gauge invariant) p-form
with (strictly) second order field equations. Such theory have recently be
fully classified for space-time dimension strictly smaller than 12. The
covariantization of these theories will also be discussed.

Conformal symmetry in the Standard Model and Gravity

I will discuss prospects of formulating simple extensions of the standard model and gravity that exhibit local Weyl symmetry in the ultraviolet. The principal advantage of such constructions is that they naturally address the gauge and gravitational hierarchy problem. Furthermore,  I will argue that Cartan-Einstein gravity provides a natural framework for conformal symmetry, as this theory contains torsion vector which can be interpreted as the Weyl vector.

Hidden symmetries and Goldstone bosons from higher dimensions?

Free massless scalars have a shift symmetry. This is usually broken by interactions, such that quantum corrections induce a quadratically divergent mass term. In the Standard Model this leads to the hierarchy problem, the question why the Higgs mass is so much smaller than the Planck mass. We present an example where a large scalar mass term is avoided by coupling the scalar to an infinite tower of massive states, obtained from a six-dimensional theory compactified on a torus with magnetic flux.

Chern-Weil theorem, Lovelock Lagrangians in critical dimensions and boundary terms in gravity actions

We show how to translate into tensorial language the Chern-Weil theorem for the Lorentz symmetry, which equates the difference of the Euler densities of two manifolds to the exterior derivative of a transgression form. For doing so we need to introduce an auxiliary, hybrid, manifold whose geometry we construct explicitely. This allows us to find the vector density, constructed out of spacetime quantities only, whose divergence is the exterior derivative of the transgression form.


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