mardi 14 juin à 16h30, salle 114
Tajron Jurić (Ruder Boković 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.