# Théorie

# Detecting gravitational waves: from kilo-Hz to nano-Hz

I will describe three major world-wide efforts to detect gravitational waves in three frequency bands. In the kilo-Hz band we use ground-based detectors (LIGO/Virgo), the milli-Hz band is accessible from space, I will describe LISA project, and, in the nano-Hz band we use millisecond pulsars (pulsar timing array). I'll briefly describe the GW sources and detection techniques in each band.

# Strong first-order phase transitions: Vorticity, droplets and gravitational waves

# Gauge theories at boundaries and corners

# No-Go theorems for ekpyrosis from string theory, and the swampland

In this talk, we present whether the new ekpyrotic scenario can be embedded into ten-dimensional supergravity. We use that the scalar potential obtained from flux compactifications of type II supergravity with sources has a universal scaling with respect to the dilaton and the volume mode. Similar to the investigation of inflationary models, we find very strong constraints ruling out ekpyrosis from analyzing the fast-roll conditions. We conclude that flux compactifications tend to provide potentials that are neither too flat and positive

# Cosmological Frontiers in Fundamental Physics 2021

The workshop is explorative in nature. It focuses on novel frontiers for the theoretical understanding of gravity and other interactions and their interface with observational cosmology and astrophysics. The goal is to understand how observations can shed light to the fundamental questions in understanding the Universe.

**Program Committee** **:**

# Amplitudes, Positivity, Modified Gravity, and Weak Gravity Conjecture

I will discuss new positivity bounds for scattering amplitudes in theories with a massless graviton in the spectrum in four spacetime dimensions.

# Hairy rotating black holes in the cubic Galileon theory

The gravitational wave detection GW170817 and its electromagnetic counterpart GRB170817A tightly constrained the speed of gravitational waves, and hence many modified theories of gravity. Among the Horndeski's scalar-tensor theories compatible with this observation, the cubic Galileon was known to admit static black holes different from the Schwarzschild solution.

# From classical to quantum models: the regularising role of integrals, symmetry and probabilities

*In physics, when a mathematical model becomes really inoperative in regard with correct predictions, one is forced to replace it with a new one. It is precisely what happened with the emergence of quantum physics. Classical models were (progressively) superseded by quantum ones through quantization prescriptions. These procedures appear often as ad hoc recipes. I will describe well defined quantizations, based on integral calculus and Weyl-Heisenberg symmetry. They are described in simple terms through one of the most basic examples of mechanics.*