Théorie

Vacuum stability without Supersymmetry: Brane dynamics, bubbles and holography

n this talk I will present some recent results on instabilities of anti-de Sitter flux compactifications in effective field theories arising from non-supersymmetric string models, namely the USp(32) and U(32) orientifold models and the SO(16) x SO(16) heterotic string. We focus on non-perturbative instabilities, framing the vacua in terms of brane stacks, analyzing their back-reacted geometry and reproducing AdS its near-horizon limit.

D-brane model building and phenomenology

I will present a review on D-brane realizations of the Standard Model and their phenomenological consequences. 
First, I will provide the basic ingredients of D-brane (open string) models which are useful for model building. 
Next, I will use them in order to embed the Standard Model in open string vacua. 
Finally, I will discuss new gauge fields and new matter particles which are predictions of the D-brane realizations of the Standard Model described above.
 

Miniworkshop on Holographic QCD at high densities, neutron stars and gravitational waves

This one-day workshop will bring together theorists working on the AdS/CFT correspondence, nuclear physics, and General Relativity for an interdisciplinarly exchange aimed at developing a consistent holographic picture of QCD matter at high density, from model building to the description of compact objects and observation via gravitational wave signals. Invited speakers include: Umut Gursoy (Utrecht U); Matti Jarvinen (Utrecht U. and Tel Aviv U.); Niko Jokela (Helsinki U.); Micaela Oertel (LUTH); Eric Gourgoulhon (LUTH). 

Programme:

Singularity avoidance, clocks and primordial power spectrum 

There are ways to cure the singularity problem in cosmology
by means of quantum effects. In the process, one encounters
the question of time, which can for instance be addressed by
using an internal degree of freedom. Applying such a method
to an anisotropic Bianchi I model where the shear serves as a
clock, I show that some generic features can be obtained for
the trajectory of the average scale factor, all avoiding the
singularity and reaching similar asymptotic states, deemed
semi-classical. Using a trajectory approach yields similar

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.

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