“The Cosmic Neutrino Background” with Julien Lesgourgues (RWTH Aachen, Germany)

Since neutrinos are known to be very light and elusive, they are often thought to play a very small part in the history of the universe. This is all but true. A numerous population of neutrinos, known as the Cosmic Neutrino Background, was produced in the early universe and has been staying around since then. Neutrinos have actually been the second most numerous particle in the universe for billions of years, and they were the second contributor to the total energy budget of the universe over most of the initial 50 000 years. These neutrinos are very difficult to measure directly, but we have several indirect (although very clear) indications of their presence. The next generation of cosmological observations will probe this component in more detail, in order to test neutrino properties and weigh their masses.

Julien Lesgourgues is a professor at RWTH Aachen University, Germany, since 2015. He graduated in France at Ecole Polytechnique and received his PhD from the University of Tours. He has occupied various postdoc and junior staff positions at SISSA (Trieste), LAPTh (Annecy), CERN (Geneva) and EPFL (Lausanne). Julien Lesgourgues is a theoretical cosmologist, specialised in the comparison of cosmological models with observations. He is a leading developer of numerical codes simulating the evolution of the whole universe on the largest scales, from the beginning of inflation until today. As a member of the Planck satellite collaboration, he shared the Gruber Cosmology Prize 2018. He is currently a member of the Euclid satellite collaboration. Julien Lesgourgues co-authored more than two hundred publications and a couple of textbooks including one on Neutrino Cosmology (CUP 2013).

Webinar was recorded on September 22, 2022