Antimatter and Gravitation

GBAR project

Our group is part of the international collaboration GBAR (Gravitational Behavior of Antihydrogen at Rest), whose aim is to measure the effect of gravity on antihydrogen atoms in the gravitational field of the Earth. The GBAR experiment is currently being constructed at CERN. The production of antihydrogen goes through a series of steps involving the creation, trapping, and cooling of positrons and antiprotons, as well as the formation of positronium atoms. Our group contributes to the study of the cross-sections of antiproton-positronium reactions, the cooling and trapping of antimatter plasmas, and the investigation of exotic states of antimatter under extreme conditions. We also explore the cosmological consequences of the possible discovery of negative mass for antimatter particles.


Evolution of the power spectra for the cases Dirac-Milne (top panel) and ΛCDM (bottom panel), for different cosmological redshifts z. The thick lines correspond to the present epoch (z=0).

The presence of complex hierarchical gravitational structures is one of the main features of the observed universe. Here, structure formation is studied both for the standard (ΛCDM) cosmological model and for the Dirac-Milne universe, a matter-antimatter symmetric universe that was recently proposed as an alternative “coasting” cosmological scenario. One-dimensional numerical simulations reveal the analogies and differences between the two models. Although structure formation is faster in the Dirac-Milne universe, both models predict that it ends shortly before the present epoch, at cosmological red-shift z ≈ 3 for the Dirac-Milne cosmology, and at z ≈ 0.5 for the ΛCDM universe. The present results suggest that the matter power spectrum observed by the Sloan Digital Sky Survey might be entirely due to the nonlinear
evolution of matter and antimatter domains of relatively small initial dimensions, of the order of a few tens of parsecs comoving at cosmological redshift z = 1080.

Selected publications