Cédric Deffayet, Physicist

Former CNRS Research Director at IHES (2017-2020)

Cédric Deffayet works on theoretical physics, at the interface between cosmology, gravitation (general relativity and its extensions) and high energy theoretical physics, particularly superstring theory.

Recently, Cédric Deffayet continued his research on massive gravity and field theories with actions containing derivative interactions and/or superior derivatives. For the first time, he thus obtained the formulation of a theory of a massive graviton propagating over an arbitrary space-time. He was able to deduce the existence of partially zero-mass gravitons (called PM) on non-Einstein space-time.

Cédric Deffayet also studied the question of the construction of coherent interactions for a multiplet of PM gravitons on Anti-de Sitter spaces, proving a uniqueness theorem for a cubic interaction. Continuing this work, a consistent and completely non-linear theory was obtained for the first time for two or more PM gravitons.

Cédric Deffayet also studied the coupling to matter in certain scalar-tensor theories of the type “beyond the Horndeski theories” and has been able to characterize different cases depending on whether or not this coupling changes the counting of degrees of freedom. Finally, domain walls of a new type (unsupported by a potential) have been highlighted in scalar theories of the “k-essence” type.

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