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Théorie

Black holes in higher-derivative scalar-tensor theories

Orateur: 
B. Goutéraux (APC)
Lieu: 
454A - Luc Valentin
Horaire: 
Tuesday, 3. July 2012 - 14:00

We consider classes of higher-derivative scalar-tensor theories, relevant for applications to modified theories of gravity (Galileons). They can be obtained from dimensional reduction and admit exact analytical black hole solutions. We describe their properties, in particular the presence of geometric horizons which dress otherwise naked singularities. If time permits, we will discuss some applications to holography.

Gauss-Bonnet braneworld redux: A novel scenario for the bouncing universe

Orateur: 
H. Maeda (CECs, Chile)
Lieu: 
454A - Luc Valentin
Horaire: 
Tuesday, 17. July 2012 - 14:00

We propose a new scenario for the bouncing universe in a simple five-dimensional braneworld model in the framework of Einstein-Gauss-Bonnet gravity, which works even with ordinary matter on the brane. In this scenario, the so-called branch singularity located at a finite physical radius in the bulk spacetime plays an essential role. We show that a three-brane moving in the bulk may reach and safely pass through it in spite that it is a curvature singularity. From the bulk point of view, this process is the collision of the three-brane with the shell of branch singularity.

Brane interactions: space dimensionality, inflation, cosmic superstrings

Orateur: 
Mairi Sakellariadou (King's College, London)
Lieu: 
734A-Gris (UNUSUAL ROOM)
Horaire: 
Monday, 11. June 2012 - 14:00

I will discuss various aspects of  brane cosmology.
I will first highlight how brane interactions can lead to our three-dimensional universe.
I will then investigate brane inflationary models and their consistency with supergravity constraints.
I will finally discuss some aspects of cosmic superstrings, formed at the end of brane inflation,  whose rich phenomenology
may offer a window to test string theory.

Supersymmetric hybrid inflation along waterfall trajectories

Orateur: 
Sebastien Clesse (DAMTP, Cambridge)
Lieu: 
366A - Klimt (UNUSUAL ROOM)
Horaire: 
Tuesday, 12. June 2012 - 14:00

I will identify a new inflationary regime for which more than 60 e-folds are generated classically during the waterfall phase occuring after the usual hybrid inflation. By performing a bayesian Monte-Carlo-Markov-Chain analysis, this scenario can be shown to take place in a large part of the parameter space of the model. When this occurs, the observable perturbation modes leave the Hubble radius during waterfall inflation.

A statistical Approach to Multifield Inflation: Many-field perturbations beyond Slow Roll

Orateur: 
Sebastien Renaux-Petel (DAMTP, Cambridge)
Lieu: 
454A - Valentin
Horaire: 
Tuesday, 5. June 2012 - 14:00

We develop a numerical statistical method to study linear cosmological fluctuations in inflationary scenarios with multiple fields, and apply it to an ensemble of six-field inflection-point models in string theory corresponding to a D3-brane moving in a conifold region. The latter are concrete microphysical realizations of quasi-single field inflation, in which scalar masses are of order the Hubble parameter and an adiabatic limit is reached before the end of inflation. We find that slow-roll violations, bending trajectories and ``many-field'' effec

Higher order Post-Newtonian corrections via Effective Field Theory

Orateur: 
Michele Levi (Ben-Gurion U. and Weizmann Institute)
Lieu: 
454A - Valentin
Horaire: 
Tuesday, 22. May 2012 - 14:00

Over the last decade considerable worldwide efforts have been invested in order to detect gravitational radiation. Inspiralling binary systems of black holes, which can be described analytically by the post-Newtonian (PN) approximation of GR, are promising candidate sources of gravitational waves signals. For a successful detection of such signals, PN corrections are required to high orders.

Black holes, fluids and the Gregory-Laflamme instability

Orateur: 
Marco Caldarelli (LPT Orsay)
Lieu: 
454A - Valentin
Horaire: 
Tuesday, 15. May 2012 - 14:00

In dimensions higher than four, black holes exhibit a much richer dynamics, and qualitatively new phenomena emerge. I will review their properties and show how deviations from the familiar four-dimensional behavior can be traced back to the emergence of widely separated scales in the system. We will see that those are the regimes in which instabilities can arise and the black hole behaves effectively as a fluid that lives on a dynamical world volume.

The first law of binary black hole mechanics

Orateur: 
Alexandre Le Tiec (Maryland U.)
Lieu: 
454A - Valentin/Klee
Horaire: 
Tuesday, 17. April 2012 - 14:00

First laws of black hole mechanics, or thermodynamics, come in a variety of different forms. We establish a first law of mechanics for binary systems of point masses moving along circular orbits. This relation is derived from first principles in General Relativity, and is explicitly shown to hold up to very high orders in the post-Newtonian approximation. Analogies are drawn with the single and binary black hole cases, revealing intriguing formal relations between point masses and black holes.

How to Solve a CFT in D > 2: The Resurgent Bootstrap and the 3D Ising Model

Orateur: 
Sheer El-Showk
Home Institute: 
Ipht (CEA)
Lieu: 
646A - Mondrian
Horaire: 
Tuesday, 10. April 2012 - 14:00
In recent years the conformal bootstrap has emerged as a surprisingly powerful tool to study CFTs in dimensions greater than two.  In this talk I will explain how crossing symmetry of the four-point function of scalar operators can be used to extract very non-trivial constraints on the spectrum of a putative CFT in arbitrary spacetime dimension. Applying these techniques in D=3 we will find that the 3D Ising model lies at a special point in the space of CFTs.

A new window on primordial non-Gaussianity

Orateur: 
Enrico Pajer (Princeton U.)
Lieu: 
454A - Valentin
Horaire: 
Monday, 2. April 2012 - 14:00

We know very little about primordial curvature perturbations on scales smaller than about a Mpc. I review how mu-type distortion of the Cosmic Microwave Background spectrum provides the unique opportunity to probe these scales over the unexplored range from 50 to $10^4 Mpc^-1$.

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