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Theorique d'Orsay

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Agenda > Séminaires / Seminars > Jeunes Dernier ajout : mardi 18 avril 2017.

Séminaire 2015-2016

-  mardi 14 juin à 16h30, salle 114

Tajron Jurić (Ruder Bošković Institute) : Noncommutative geometry and physics,

I will give a short introduction of noncommutative geometry and an overview of its applications in physics. The most interesting ones are : 1) The reformulation of the Standard Model of particle physics 2) Non-commutative quantum field theory as a gate to quantum gravity. I will keep this talk non-technical and explain the main ideas for introducing noncommutative geometry and how we can use it in physics.

-  mercredi 6 avril à 16h30, salle 114

Lais Schunk (CEA/IPhT) : Analytic control of jet substructure

This presentation has two main goals. The first one is to present a short introduction to the concept of boosted jets and jet substructure at the LHC. The second one is to make a comparison between techniques that discriminate two-pronged signals from QCD background using constraints on energy flow within boosted jets. To that aim, I focus on three commonly-used jet shapes : N-subjettiness, the mass-drop parameter and energy-correlation functions. For each of these shapes, I show that we can understand their performance from first-principle QCD calculations. I also compare our findings with Monte-Carlo simulations.

-  mercredi 30 mars à 16h30, salle 114

Luca Lionni (LPT Orsay) : About matrix models, random geometry and 2D quantum gravity

I will discuss the link between 2D-quantum gravity and random triangulations of 2D surfaces, which was developed in the late 70’s and 80’s. Expressing the sum over geometries as a sum over random triangulations, one obtains a discrete equivalent to the Einstein-Hilbert partition function of pure gravity, which can be expressed as the perturbative expansion of some hermitian matrix models. In the continuum limit, the results of computations agree with those of 2D-gravity coupled to a conformal field theory obtained from continuous Liouville theory.

-  mercredi 17 février à 16h30, salle 114

Olcyr Sumensari (LPT Orsay) : New Physics and Lepton Flavour Violation

Lepton flavor is an accidental symmetry of the Standard Model (SM) which is broken, since neutrinos are massive and oscillate between different flavors. Nonetheless, the smallness of neutrino masses ensures that all decays with lepton flavor violation (LFV), such as ? ? e  ?,remain highly suppressed and basically not observable. These processes are therefore very clean probes of physics beyond the Standard Model (BSM). After an introduction to the SM and our main motivations to invoke physics BSM, I will discuss the role of LFV searches in the quest for New Physics. Finally, I will briefly comment on some recent anomalies recently observed at LHCb and the possible connection with LFV.

-  mercredi 2 décembre à 16h30, salle 114

Tetiana Moskalets : Liouville mode in Gauge/Gravity Duality

We establish solutions corresponding to AdS static charged black holes with inhomogeneous 2D horizon surfaces. The inhomogeneity is encoded in a distribution function, entering the internal horizon metric ansatz, which depends on horizon coordinates and satisfies the elliptic Liouville equation. Using the obtained solution we calculate transport coefficients in strongly coupled dual media (e.g. quark-gluon plasma) in the hydrodynamic limit of Gauge/Gravity duality. One can see that presence of nonuniformity on black hole horizon results in the exponential suppression in the charge diffusion coefficient and in the shear viscosity-per-entropy density ( ?/s) ratio. We discuss subtleties of the developed approach for a planar black hole with inhomogeneous horizon in more detail and find, among others, a trial inhomogeneity distribution function, which fits all the range of experimentally measured at RHIC and at the LHC values of  ?/s ratio. Generalization to higher-dimensional AdS space reveals two different charge diffusion coefficients (and, hence, DC conductivities) in higher-dimensional effective strongly coupled dual media. We formulate conditions under which the appropriate ratio of different conductivities is qualitatively the same as that of observed in anisotropic strongly coupled fluid.

-  mercredi 25 novembre à 16h30, salle 114

Julien Baur (CEA-Irfu/SPP) : Measuring the mass of neutrinos using a pierced aluminium plate

As near massless particles, neutrinos behave like an additional radiation component in the early Universe and thus hinder structure formation and growth. Perturbations on sub-galactic scales are exponentially damped. The matter power spectrum on these relevant scales is constructed from absorption features imprinted in the spectra of distant quasars, which encode neutral Hydrogen regions along the quasar line-of-sight. The large sky coverage and completeness of the Sloan Digital Sky Survey (SDSS) enables the construction of the distribution of neutral Hydrogen densities in the intergalactic medium, from the quasar spectra taken by one of its four surveys : the Baryon Oscillations Spectroscopic Survey (BOSS). Contrast between the transmitted flux in the Lyman-alpha forest and the power spectrum obtained by hydrodynamics simulations issues the tightest bounds on the sum of neutrino masses to date. The scales probed by BOSS spectra also issue the tightest constraints on the mass of warm dark matter particles, including a hypothetical sterile neutrino.