Séminaire

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.

On the perturbative expansion at high temperature and implications for cosmological phase transitions

A first-order phase transition in the early universe would have given rise to a stochastic gravitational wave background which may be observable today. In this talk, I will focus on the crucial problem of making reliable predictions of the thermodynamics of such phase transitions in the face of infrared Bose enhancements at high temperature. Such enhancements lead to large theoretical uncertainties in perturbation theory at low orders. I will unravel the structure of the perturbative expansion in this context, and of the misalignment between loop and coupling expansions.

Gravitational waves from the early-universe turbulent sources

A space-based laser interferometer, pioneered by NASA's LISA concept and now a ESA cornerstone mission, will enable direct detection of gravitational waves at lower frequencies than LIGO, without being limited by seismic noise. Perhaps the most intriguing source for LISA is the stochastic gravitational wave background produced by turbulent plasma motions in an early-universe, particularly at the electroweak energy scale.

Two recent topics in gravitational-wave cosmology: Binary resonance searches and nonlinear memory from cosmic strings

In the first half of this talk, I will discuss how binary systems can be used as dynamical detectors of gravitational waves (GWs). Since the passage of GWs through a binary perturbs the trajectories of the two bodies, we can infer the presence of a GW signal by searching for changes in the binary's orbital parameters. In the presence of a stochastic GW background (SGWB) these changes accumulate over time, causing the binary orbit to execute a random walk through parameter space.

The astrophysics of black hole binaries in the era of gravitational wave astronomy

Black holes (BHs) cover a wide range of mass: from the stellar BH binaries detected with LIGO / Virgo to the massive BHs residing at the center of galaxies. Both these populations will be detectable in future by LISA at low-frequency. In this talk, I will provide a general overview of the current detections from LIGO / Virgo, describing the current state-of-the-art and I will highlight the potential of the LISA mission.

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