New Graduate Phd : Dr. Vivien Bonvin

The expansion rate of the Universe, also called the Hubble constant - or H0 - is one of the most sought-after prizes in modern cosmology. The currently best model to explain our observations of the Universe is called LambdaCDM, and postulates notably the existence of dark matter and dark energy as the main components of the Universe. A change in the nature of dark energy would produce a change in the predicted value of H0, that is to be compared with direct measurement.

Time-delay cosmography is a simple and elegant technique allowing a direct measurement of H0. Known since the second half of the 20th century, this technique is blossoming only now thanks to the hard work of the H0LiCOW collaboration. At its heart are the time-delay measurements between the multiple images of a background source strongly lensed by a foreground galaxy. Over the course of my PhD, I developed curve-shifting algorithms to tackle this problem, successfully demonstrating both their excellent accuracy and precision. Along with other long-term effort from my collaborators, I turned my time-delay estimates into cosmological constraints, making time-delay cosmography one of the current most precise direct probe of the Universe expansion rate.