Séminaire

Probing inflation at small scales with the stochastic gravitational wave background

Departures of inflation from the single-field slow-roll paradigm, also known as “features”, are common in ultraviolet completions of inflation. These departures can be significant at small scales where Cosmic Microwave Background data is not constraining. I will explain how such features during inflation can be tested through their gravitational wave signal. In particular, I will show that features lead to a characteristic oscillation in the stochastic gravitational wave background.

Cosmological observables and their combinatorial origin

QFT in nearly dS space-times and, more generally, in FRW backgrounds allows us to describe correlations at the end of inflation. However, how to extract fundamental physics out of them is still a challange: we do not even know how fundamental pillars such as causality and unitarity of time evolution constrain them. In this talk I will report on a recent program that aims to construct quantum mechanical observables in cosmology directly from first principles without making any reference to time evolution.

Results and open questions on two coasting cosmological models

The ΛCDM Model accurately reproduces most cosmological observations, including primordial nucleosynthesis, the cosmic microwave background radiation, and baryonic acoustic oscillations. However, standard baryonic matter constitutes only 5% of the total content of the ΛCDM universe, while the dominant components – cold dark matter (≈25%) and dark energy (≈70%) – are yet unobserved.

Spinning black holes fall in Love

The open question of whether a black hole can become tidally deformed by an external gravitational field has profound implications for fundamental physics, astrophysics and gravitational-wave astronomy. Love tensors characterize the tidal deformability of compact objects such as astrophysical (Kerr) black holes under an external static tidal field. We prove that all Love tensors vanish identically for a Kerr black hole in the nonspinning limit or for an axisymmetric tidal perturbation. In contrast to this result, we show that Love tensors are generically nonzero for a spinning black hole.

Gravitational Bremsstrahlung in the Post-Minkowskian expansion

I will discuss the scattering of two compact objects interacting via gravity, using the so-called world-line Effective Field Theory approach in the post-Minkowskian expansion (i.e. expanding in the Newton's constant G but not in the velocities). In particular, I will focus on the computation of classical observables such as the total emitted momentum. This is obtained by phase-space integration of the graviton momentum weighted by the modulo squared of the radiation amplitude.

Effective field theory approach to thermal bubble nucleation

The possibility of observing a stochastic gravitational wave background originating from a cosmological first-order phase transition elicits interest in studying the transitions. Currently, a limiting factor in accurately determining the gravitational wave spectrum from an underlying microphysical model is the calculation of the nucleation rate. I will discuss recent work in which we have proposed a new effective field theory (EFT) framework for determining the thermal nucleation rate in high-temperature QFTs.

Pages

S'abonner à RSS - Séminaire