Observing quantum gravity in gravitational waves

Gravity can be embedded into a renormalizable theory by means of adding quadratic in curvature terms.
However, this at first leads to the presence of the Weyl ghost. It is possible to get rid of this ghost if the
locality assumption is weakened and the propagator of the graviton is represented by an entire function
of the d'Alembertian operator without new poles and zeros. Models of this type admit a cosmological
solution describing the R^2, or Starobinsky, inflation. We study graviton production after inflation in

Tests of gravity with DES Year 3 weak lensing

The new weak lensing measurements from the first three years of observation by the Dark Energy Survey offer a unique opportunity to constrain deviations from General Relativity, our theory of gravity. Weak gravitational lensing is indeed a powerful probe of the growth of structures. As such it offers a window on the laws of gravity on cosmological scales. We thus used DES Year 3 weak lensing data to test the validity of General Relativity (GR) to a new regime, and explore modifications to GR as an alternative to dark energy.

Scalar-vector gauge unification and quantum de Sitter geometry

We consider the massless minimally coupled scalar field in the de Sitter ambient space formalism as a gauge potential or connection field. We construct the scalar gauge theory by helping an arbitrary constant five-vector field B analogous to the standard gauge theory. The Lagrangian density of the interaction between the scalar and spinor fields is presented in this framework. The Yukawa potential can be extracted from this Lagrangian density at the null curvature limit by an appropriate choice of a constant five-vector field.

The Boostless Bootstrap in the era of Large-Scale Structure

After an introduction on recent efforts in extracting information about the early Universe from galaxy clustering surveys and on the "Boostless Cosmological Bootstrap" program, I review recent results and developments in this program, especially in light of recent measurements of the four-point function of BOSS galaxies.

Gravitation group Seminar: Rachel Gray - Cosmology with Dark Sirens and Galaxy Catalogues

Dear all,

On Monday, October 17 at 10.00 we will be welcoming Rachel Gray (Queen Mary University of London) for the gravitation group seminar. The seminar will take place online - the zoom link can be found below.

Rachel will talk about cosmological constraints from gravitational wave dark sirens and galaxy catalogs.

Title:
Cosmology with Dark Sirens and Galaxy Catalogues

Abstract:

Local sources of 100 TeV neutrinos

Multi-messenger data of high energy neutrinos by IceCube and gamma-rays by Tibet AS-gamma show new signal at 100 TeV energies outside of Galactic plane but below 20 degrees from it. This mysterious signal challenge conventional cosmic ray models, which predict major Galactic signal from Galactic plane and no significant flux at high galactic latitudes, as seen at GeV energies by Fermi LAT telescope.

Here we show that main assumption of continues distribution of cosmic rays in Galaxy is broken at PeV energies.

Gravitation Group Seminar: Nicola Franchini: Constraining modifications of black hole perturbation potentials near the light ring with quasinormal modes

On Monday, October 3 at 10.00 we will be welcoming Nicola Franchini (APC) for the gravitation group seminar. The seminar will take place in room 631B, (a zoom link can be found below).
Nicola will talk about the constraints from quasinormal modes on black hole perturbation potentials.

Constraining modifications of black hole perturbation potentials near the light ring with quasinormal modes

Abstract

Theory and observational constraints in nonlocal gravity

I will present selected field theoretical aspects and Bayesian model selection studies in a particular class of modified gravity theories, so-called nonlocal gravity theories. In particular, I will focus on three nonlocal gravity models that have been proposed for explaining the late-time acceleration of the expansion of the universe and have been shown to provide a statistically equivalent fit to LCDM given recent cosmological data.

Primordial Black Holes from Inflation

Abstract:
It is now recognized that primordial black holes (PBHs) may be produced in various models of inflation in the early universe. In this talk, I review several different scenarios of PBH formation from inflation, each of which has rather distinct features. Then I discuss how these models may be observationally tested in the not-so-distant future, particularly by gravitational wave observations.

Gravitational lensing for dark matter explorations inside the Milky Way and for cosmological investigations

Abstract. I’ll show the analysis we perform on gravitational microlensing signatures and how we estimate gravitational microlensing parameters to obtain information about several components of the dark matter in our galaxy like free-floating planets, brown dwarfs, primordial black holes, making use of actual and future space-based telescopes: Euclid, THESEUS, Gaia, Roman, etc.

LABORATOIRE

ASTROPARTICULE & COSMOLOGIE

Séminaire