# 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 2020

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 Classical models were (progressively) superseded by quantum ones through quantization prescriptions.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

# 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.

# Teleparallel gravity (TEGR) as a gauge theory: Translation or Cartan connection?

We question the status of TEGR, the Teleparallel Equivalent of General Relativity,
as a gauge theory of translations. We observe that TEGR (in its usual translation-gauge view) does not seem to realize the generally admitted requirements for a gauge theory for some symmetry group G: namely it does not present
a mathematical structure underlying the theory which relates to a principal G-bundle and the choice of a connection on it (the gauge field). We point out that, while it is usually presented as absent, the gauging of the