# Théorie

# Generalized Multi-Scalar-Tensor theory in arbitrary dimensions

After a brief introduction on modified gravity, scalar-tensor theories and the Ostrogradski theorem, I will talk about the most-general multi-scalar-tensor theory that is free of Ostrogradski ghosts, i.e., with equations of motion with derivative order up to two [arxiv.org/abs/1210.4026]. I will also touch upon the possible applications of this powerful general framework.

# Could quantum theory explain the origin of the inflationary period?

# Isotropy-breaking in Quantum Cosmology

We present a new perspective in QFT on quantum cosmological space-times. Naively, the semiclassical limit of a quantum space-time can be taken by averaging the gravitational operators on a semiclassical state of the geometry. The result is an effective classical metric (which in general does not obey the Einstein equations).

# How to shape a black hole with matter fields

The main interest of the work exposed in this seminar is to explore new black hole solutions in a more general framework than General Relativity. A first extension will be detailed with the introduction of higher dimensions and p-form fields. These fields constitute the natural generalization of the electromagnetic interaction. We will build in this context new static black hole solutions where p-form fields allow to shape the geometry of the horizon.

# Solving the general cosmological singularity problem

To begin with, we present the big bounce transition of the quantum FRW model in the setting of loop quantum cosmology. We determine the physical self-adjoint Hamiltonian generating the dynamics. It is used to define, via the Stone theorem, an evolution operator of the quantum system. We examine the properties of the expectation values of physical observables in the process of the quantum big bounce transition. The dispersions of observables are studied in the context of the Heisenberg uncertainty principle.

# Higgs-inflation and recent LHC results

`The only fundamental scalar field of the Standard Model of particle ``physics - the Higgs field - can serve also as the inflaton in the ``early Universe, if non-minimal coupling to gravity is switched on. ``We discuss this idea, in particular: similarity to the Starobinsky ``
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`Japan in Paris workshop`

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Orateur:
APC Japanese postdocs and visitors
Lieu:
454A Valentin
Horaire:
Thursday, 25. October 2012 - 14:00
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This is a mini workshop organized to introduce the research of several Japanese new postdocs and visitors at APC. Topics include general relativity (e.g. black hole physics) and cosmology (e.g. theory of cosmological perturbations).

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Orateur:
Masahide Yamaguchi
Home Institute:
Department of Physics, Tokyo Institute of Technology
Lieu:
483A Malevitch
Horaire:
Tuesday, 30. October 2012 - 14:00
Orateur:
Takahisa IGATA (APC)
Lieu:
483A Malevitch
Horaire:
Tuesday, 23. October 2012 - 14:00
Orateur:
George Zahariade (APC)
Lieu:
Salle 483A - Malevitch
Horaire:
Tuesday, 16. October 2012 - 14:00
`

# Supersymmetric DBI inflation

# Stationary Closed Strings in Five-dimensional Flat Spacetime

We discuss stationary rotating closed Nambu-Goto strings in five-dimensional flat spacetime. The stationary string is defined as a worldsheet that is tangent to a timelike Killing vector. The Nambu-Goto equation of motion for the stationary string is reduced to the geodesic equation on the orbit space of the isometry group action generated by the Killing vector. We take a linear combination of a time-translation vector and space-rotation vectors as the Killing vector, and explicitly construct general solutions of stationary rotating closed strings in five-dimensional flat spacetime.

# A new way to count degrees of freedom in dRGT massive gravity

Recently, there has been a lot of progress in the area of non-linear massive gravity. In particular a theory free from the “Boulware-Deser ghost” has been proposed by de Rham, Gabadadze, Tolley (dRGT). We clarify some of its existing formulations, and provide a new and elegant alternative approach to the counting of the number of degrees of freedom of dRGT theory.