Théorie

Non-Fierz-Pauli bimetric theory from quadratic curvature gravity on Einstein manifolds

I will show that, in four-dimensional spacetimes with an arbitrary
Einstein metric, with and without a cosmological constant, perturbative dynamical degrees of freedom in generic quadratic-curvature gravity can be decoupled into massless and massive parts. The massive part has the structure iden-ical to, modulo the

Stability properties in mimetic gravity theories

Motivated as a possible unified description for dark matter and dark
energy, we analyze the cosmological applications and the stability
conditions of Mimetic Gravity models. In connection to the fact that
these models have been recently shown to be plagued by instabilities, we
show that for the original mimetic matter model the ghost/tachyon instability
for perturbations around the FLRW background can be interpreted as the
standard Jeans instability of dust.
Proposed as a solution for the instability problems, we discuss mimetic

Stochastic inflation in the phase space

Inflation is currently the leading paradigm describing the physical conditions that prevail in the very early universe. During this epoch, quantum fluctuations are extracted out of the vacuum and amplified to cosmological perturbations at astronomical scales, later seeded CMB anisotropies and large-scale structures. As inflation proceeds, this inflow of super-horizon perturbations may impact on the large-scale dynamics of the universe, potentially perturbing the inflationary trajectory.

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

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