Théorie

An effective holographic approach to QCD 

In this seminar I will describe a holographic approach to QCD where 
conformal symmetry is broken explicitly in the UV by a relevant operator 
O. This operator maps to a five dimensional scalar field, the dilaton, 
with a massive term. Implementing also the IR constraint found by 
Gursoy, Kiritsis and Nitti, an approximate linear glueball spectrum is 
obtained which is consistent with lattice data. Finally, I will describe 
the evolution of the model parameters with the conformal dimension of O. 
This will suggest a map between the QCD anomaly and the trace anomaly of

The Linde problem on R2 x S1 x S1

Thermal field theory provides the natural framework to describe the thermodynamic properties and to study phase transitions of systems described by quantum field theories, in particular, the quark-gluon plasma. However, its the perturbative realization faces important technical difficulties whenever massless bosons are considered, due to divergences in the IR sector.

Holographic solids

What is the holographic dual of an ordinary solid? Using insight from effective field theory (EFT), I will argue that an answer is provided by an SO(d) magnetic monopole in (d+1)-dimensional AdS space. We call such field configuration “solidon”. The low-energy spectrum of the boundary theory can be derived analytically from the gravity dual, and the result confirms that the effective theory consists of a set of phonons having dispersion relations that match those expected from EFT.

Radiative decay of keV-mass sterile neutrinos in a strongly magnetized plasma

The radiative decay of sterile neutrinos with typical masses of 10 keV 

is investigated in the presence of a strong magnetic field and degenerate

electron plasma. The modification of the photon dispersion relation by 

the active external medium is taken into account. The limiting cases 

of relativistic and non-relativistic plasma are analyzed. The decay rate 

in a strongly magnetized plasma as a function of the plasma electron number 

density is compared with the unmagnetized case. It Was found that the strong 

Invitation to Random Tensors

Random matrices are ubiquitous in modern theoretical physics and provide insights on a wealth of phenomena, from the spectra of heavy nuclei to the theory of strong interactions or random two dimensional surfaces. The backbone of all the analytical results in matrix models is their 1/N expansion (where N is the size of the matrix). Despite early attempts in the '90, the generalization of this 1/N expansion to higher dimensional random tensor models has proven very challenging.

Solving the flatness problem with an anisotropic instanton in Horava-Lifshitz gravity

The first half of this talk reviews the basic construction and some
known cosmological implications of a renormalizable theory of
gravitation called Horava-Lishitz gravity. In particular, I will
explain that (i) the anisotropic scaling with the dynamical critical
exponent z=3 renders a field theory of gravity renormalizable, that
(ii) the same anisotropic scaling solves the horizon problem and leads
to scale-invariant cosmological perturbations even without inflation
and that (iii) the infrared instability of the so-called projectable

Intergalactic magnetic fields

I will review the status of observations  and modelling of intergalactic magnetic fields (IGMF), with an update on recent results from gamma-ray searches. These fields, present in the voids of the Large Scale Structure (LSS) are either relics from the Early Universe or are produced in result of the star formation feedback on the LSS. I will put the observational results in the context of to possible mechanisms of generation and evolution of the IGMF.

Testing gravity with relativistic effects in large-scale structure

The distribution of galaxies provides a powerful way to probe the properties of our universe. In order to exploit this observable properly it is necessary to understand what we are really measuring when we look at the large-scale structure. Since our universe is not completely homogeneous and isotropic, we only see a distorted picture of our sky. In this talk, I will discuss the various relativistic effects that distort our observations.

Infrared QCD: perturbative or non perturbative?

A model suited for calculating correlation functions in QCD from the ultraviolet to the infrared is reviewed. The model consist in standard Faddeev-Popov Lagrangian for Landau gauge with an extra mass term for gluons. It is shown that once this mass term is included, two and three point correlation functions can be calculated with good precision at one-loop order even at very low momenta in the quenched approximation. After that, the inclusion of quarks is analyzed.

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