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.

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

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 Classical models were (progressively) superseded by quantum ones through quantization prescriptions.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.

Dark energy and fundamental physics: the landscape, the swampland, and all that

While theoretical efforts continue to explore possible explanations for the late-time cosmic acceleration, as well as the problem of the cosmological constant, we expect future cosmological surveys to judge against or for many of the proposed theories. In this talk, I will first review the status of models of dark energy provided by fundamental physics (supergravity and string theory) by presenting, as an example, a recently discovered class of $\alpha$-attractor models of quintessential inflation which combine dark energy and inflation in a unified framework.

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