The recent observations of the Cosmic Microwave Background by the Planck satellite strongly support the standard cosmological model, defined by just a few independent parameters. Two of them in particular still require a theoretical explanation: the small deviation from scale invariance in the power spectrum of the initial density fluctuations, and the level of inflationary gravitational waves, detectable through B-mode polarization in the CMB. Following an introduction to inflationary cosmology, I will describe a recently developed class of inflationary models, motivated by maximal supersymmetry and string theory, that gives specific targets for future B-mode experiments. These models are based on the hyperbolic geometry of the Poincare disk, which is beautifully represented by Escher's picture Circle Limit IV.

Please note: The Colloquium Ehrenfestii takes place on Wednesday evenings starting at 19:30 hours in the main auditorium of the Oort building. Before the Colloquium, there is a common dinner in the canteen located on the ground floor of the  Oort building. The dinner starts at 18:00 hours sharp and is free of charge, under the condition that one attends the colloquium and that one has made a reservation before noon on the Tuesday preceding the colloquium.The registration form is only accessible from within the University (to block spammers); if you would like to register for the dinner from outside the University, please send an email to fran@lorentz.leidenuniv.nl   The revolving doors to the Oort building  are accessible until 9 pm after that they are locked and one should instead use the sliding doors directly adjacent to the Huygens building: these can be opened with an electronic key (seek help from locals).