Théorie

A very light dilaton and naturally light Higgs

We study a very light dilaton, arising from a scale-invariant ultraviolet theory of the Higgs sector in the standard model  of particle physics. Imposing the scale symmetry below the ultraviolet scale of the Higgs sector, we alleviate the fine-tuning problem associated with the Higgs mass. When the electroweak symmetry is spontaneously broken radiatively  a la Coleman-Weinberg, the dilaton develops a vacuum expectation value away from the origin to give an extra contribution  to the Higgs potential so that the Higgs mass is around the electroweak scale.

Caustic free completion of k-essence

Both k-essence and the pressureless perfect fluid develop caustic singularities at finite time. We explore the connection between the two and show that they belong to the same class of models, which admits the caustic free completion by means of the canonical complex scalar field. Specifically, the free massive/self-interacting complex scalar reproduces dynamics of pressureless perfect fluid/shift-symmetric k-essence under certain initial conditions in the limit of large mass/sharp self-interacting potential.

Gravitational waves from first-order phase transitions

LISA may be able to detect the gravitational waves from a first order phase transition at the electroweak scale. We present results from a large campaign of simulations studying a model of such phase transitions, and determine the shape of the power spectrum with unparalleled accuracy. We make concrete predictions of the detectability of sound waves from such a scenario, and note that an accurate measurement could place constraints on the underlying phase transition parameters.

Neutron stars: probing ultra dense (and hot) matter

Observed for the first time in 1967 as pulsars, neutron stars
represent the most extreme bodies known in nowadays universe. Relict of the
gravitational collapse and subsequent supernova explosion of a massive
star at the end of its life, they gather a mass of up to twice that of
our sun in a sphere with a radius of about 10 km. Their phenomenology
is very rich and complex. They are not only very compact, but they are
also rotating at frequencies of up to 700 Hz and can have strong

Two-body problem in modified gravities and EOB theory

The effective-one-body (EOB) approach has proven to be a very powerful framework to describe analytically the coalescence of compact binary systems in general relativity (GR).  In this seminar, we address the question of extending it to the frame of modified gravities, focussing on the first building block of the EOB approach; that is, mapping the conservative part of the two-body dynamics to the Hamiltonian of a single test particle in effective external fields.

Stochastic Inflation and Primordial Black Holes

In the inflationary paradigm, the transition from quantum fluctuations to classical but stochastic density perturbations plays an important role. In particular, it implies that the open quantum system comprising the super-Hubble degrees of freedom can be described with a classical stochastic theory, the “stochastic inflation” formalism. In this framework, the short-wavelength quantum fluctuations act as a classical noise on the dynamics of the super-Hubble scales.

Black hole information loss and the measurement problem in quantum theory

We will briefly review the issue of "information loss" during the Hawking evaporation of a black hole, and argue that the quantum dynamical reduction theories, which have been developed to address the  measurement problem in quantum mechanics,  possess the elements to diffuse the ``paradox”  at the qualitative and at the quantitative level, leading to what seems to be an overall coherent picture.

 

Factorization of IR Dynamics: Soft Black Hole Hair as Soft Wigs

Conserved charges associated with large gauge symmetries and Bondi-Metzer-Sachs symmetries of asymptotically Minkowski spacetime have been recently shown to give new "soft hair" for black holes --beyond mass, charge and angular momentum.  In this talk, I will outline a study of the constraint on dynamics due to these new symmetries. I will prove that they only constrain long-time, infrared dynamics, in a way that is completely factorizable. Factorization implies in particular that soft hair does not constrain the ``hard" physical processes that account for black hole microstates.

Post-Newtonian order gravitational radiation

Post-Newtonian theory enables us to predict the waveform of the gravitational waves emitted by a system of two compact objects coalescing in its inspiral phase. State-of-the-art works provide the phase of the expected signal up to 3.5PN (i.e. up to 1/c^7). Comparison with numerical relativity, as well as the promising evolution of gravitational wave detectors incite us to pursue this computation to a higher order. In our current attempt, we are reaching the phase of the signal at the 4.5PN order (i.e. 1/c^9). For this purpose, the flux emitted by such a system has to be known at 4.5PN.

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