Théorie

Consistency relations of the large scale structure and how to break them

Upcoming cosmological experiments intend to exploit the large scale structure of the Universe to get a better understanding of the observed cosmic acceleration. By measuring the power spectrum, one can constrain the equation of state of dark energy, and galaxy surveys promise great improvement over the current constraints. Galaxy surveys can also be used to gather cosmological information beyond cosmic acceleration. For example, one can derive consistency relations that can relate the bispectrum to the power spectrum for example.

Dark energy without dark energy: Observational tests and theoretical challenges

I will give an overview of the timescape cosmology. It is assumed that inhomogeneities - voids, walls and filaments - modify the average background geometry of the universe, which is no longer a simple solution of Einstein's equations with homogeneous dust. To obtain a viable phenomenology without dark energy, I provide a framework for interpreting Buchert's backreaction formalism, by revisiting fundamental issues relating to the definition of gravitational energy in a complex geometry. Cosmic acceleration is realized as an apparent effect due both to backreaction

Anisotropy of the astrophysical gravitational wave background: analytic expression of the angular power spectrum and correlation with cosmological observations

Unresolved sources of gravitational waves are at the origin of the existence of a stochastic gravitational wave background. While the computation of is mean density as a function of frequency in a homogeneous and isotropy universe is standard lore, the computation of its anisotropies requires to understand the coarse graining from local systems, to galactic scales and then to cosmology.  We derive an expression of the gravitational wave energy density valid in any general spacetime.

Long lived light scalar in the minimal left-right symmetric model

In the minimal left-right symmetric model which could accommodate the tiny neutrino masses via TeV seesaw mechanism, the neutral scalar from the right-handed symmetry breaking sector could be much lighter than the electroweak scale. We discuss the constraints on this particle from low-energy flavor observables, e.g. meson oscillations and rare decays, and find that such a light particle is necessarily long-lived, and can be searched for at the LHC via displaced signals of a collimated photon jet, if its mass is of order GeV scale.

Stueckelberg massive electromagnetism in de Sitter and anti-de Sitter spacetimes: Two-point functions and renormalized stress-energy tensors

 We discuss Stueckelberg massive electromagnetism on an arbitrary four-dimensional curved spacetime. By considering Hadamard vacuum states, we construct the two-point functions associated with Stueckelberg massive electromagnetism in de Sitter and anti-de Sitter spacetimes. We present the Hadamard renormalization of the expectation value of the stress-energy-tensor operator, and we provide its explicit expression for the Stueckelberg theory.

Chiral electrodynamics in astrophysics and cosmology

An asymmetry between left- and right-chiral lepton states can induce

additional contributions to the electromagnetic current in the presence

of magnetic fields or vortical fluid flows. In contrast to the usual Ohmic

current these chiral currents are dissipationless. They can lead to instabilities

such as the chiral magnetic effect in which magnetic fields can undergo an

exponential growth phase, similar to the dynamo effect. We discuss astrophysical

and cosmological contexts in which such effects may play a role, such as

New Directions in Dark Matter Direct Detection

Sub-GeV dark matter is a theoretically motivated but largely unexplored paradigm of dark matter. In this talk, I will discuss recent work on the direct detection of sub-GeV dark matter through dark matter-electron scattering. I will present some motivated models that can be probed with these techniques as well as projections for current and near-term noble liquid, semiconductor, and scintillator experiments. Finally, I will discuss some new techniques that may allow us to more robustly discriminate between dark matter signatures and background.

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