Séminaires

Parameter estimation in Cosmology with Cobaya and Machine-Learning
Jesus Torrado (Padova University)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

I will briefly present Cobaya, an inference framework aimed at model pipelines with complex interdependencies between parameters and intermediate quantities, and use it to illustrate some aspects of classic Bayesian inference in Cosmology. Next, I will discuss the effort by me and my collaborators towards a no-pre-training, drop-in replacement for classical parameter inference on very slow posteriors, using a Gaussian Process surrogate model that actively learns the posterior distribution and converges in O(100) fewer evaluations.

Probing gravity and its fundamental properties with radio pulsars
Paulo Freire (Max-Planck-Institut für Radioastronomie, Bonn, Germany)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

Over the last few years, a set of new results from pulsar timing has not only introduced some of the most precise tests of general relativity (GR) done to date, but have also introduced much tighter constraints on violations of a fundamental principle, the strong equivalence principle (SEP), which is embodied by GR. This was done via a direct verification of the universality of free fall for a pulsar in a triple star system and with tests of the nature of gravitational waves, in particular a search for dipolar gravitational wave emission in a variety of binary pulsars with different masses. No deviations from the SEP have been detected in our experiments. These results introduce some of the most stringent tests of GR, which introduce the tightest constraints on several classes of alternative theories of gravity and complement recent results from the ground-based gravitational wave detectors.