Julien Lesgourgues

Julien Lesgourgues is a French theoretical cosmologist known for contributions to computational cosmology and public scientific software. He is notable for co-developing Boltzmann solvers used in studies of the cosmic microwave background, large-scale structure, and neutrino physics, and for collaborations with international projects and research groups across Europe and North America.

Early life and education

Lesgourgues completed his studies in France and pursued graduate research in theoretical physics at institutions linked to École Normale Supérieure, University of Paris, and research laboratories associated with Centre National de la Recherche Scientifique and the Institut d'Astrophysique de Paris. During his doctoral and postdoctoral training he engaged with research communities connected to the Institut des Hautes Études Scientifiques, CERN, Max Planck Institute for Astrophysics, and the European Southern Observatory, interacting with researchers from groups working on cosmic inflation, Big Bang nucleosynthesis, neutrino oscillation phenomenology, and computational methods in perturbation theory.

Research career

Lesgourgues held positions at research centers including the University of Geneva and collaborated with teams at Institute for Theoretical Physics (EPFL), Laboratoire de Physique Théorique, and international consortia tied to missions such as Planck (spacecraft), Wilkinson Microwave Anisotropy Probe, and projects like Euclid (spacecraft). His career spans interactions with scientists associated with Princeton University, Institute for Advanced Study, Harvard University, California Institute of Technology, Stanford University, Fermilab, Brookhaven National Laboratory, and national agencies including NASA, European Space Agency, CNES, and IN2P3. He has participated in workshops and conferences organized by International Astronomical Union, American Physical Society, European Physical Society, and the Royal Society.

Contributions to cosmology

Lesgourgues co-developed public Boltzmann codes integral to analyses of the cosmic microwave background, matter power spectrum, and cosmological parameter estimation used by collaborations such as Planck (spacecraft), Atacama Cosmology Telescope, South Pole Telescope, and surveys like Sloan Digital Sky Survey, Dark Energy Survey, and Baryon Oscillation Spectroscopic Survey. His work addresses theoretical foundations tied to cosmological perturbation theory, scalar field dynamics in inflation, treatment of massive neutrinos in cosmological evolution, and modeling of reionization impacts on anisotropy measurements. Lesgourgues's codes and analyses have been adopted in pipelines alongside tools developed at institutions including Institut d'Astrophysique de Paris, Max Planck Institute for Astrophysics, University of Cambridge, Oxford University, Imperial College London, Kavli Institute for Cosmological Physics, and Perimeter Institute for Theoretical Physics for parameter inference in frameworks related to Lambda-CDM model, alternatives such as dark radiation scenarios, and extensions involving modified gravity and sterile neutrino hypotheses examined by collaborations like IceCube Collaboration and experiments such as Daya Bay and KATRIN.

Awards and recognition

Lesgourgues has been acknowledged by academic institutions and collaborations for software and scholarly contributions, receiving invitations to speak at major meetings organized by International Conference on High Energy Physics, Cosmology and Particle Astrophysics (CosPA), and symposia hosted by European Space Agency and National Academy of Sciences. His contributions feature in collaborative results produced by Planck Collaboration, BOSS Collaboration, and review volumes published with contributors from University of California, Berkeley, University of Chicago, Columbia University, Yale University, University of Tokyo, and Kyoto University.

Selected publications

- Lesgourgues, J.; co-authors. Papers on Boltzmann solver development used in analyses by Planck Collaboration and cited in work from Sloan Digital Sky Survey and Dark Energy Survey. - Lesgourgues, J.; review chapters on massive neutrinos and cosmology appearing in compilations with contributors from Max Planck Institute for Astrophysics, Institute for Advanced Study, and Perimeter Institute for Theoretical Physics. - Lesgourgues, J.; technical articles on cosmological perturbations and numerical methods referenced by teams at Harvard University, Princeton University, Stanford University, Caltech, and Imperial College London.

Category:French cosmologists Category:Theoretical physicists