Structure formation simulations with scattering between dark energy and baryons

Our Universe is full of unknowns, among them one of the most mysterious is, no doubt, dark energy (DE), the entity responsible for cosmic acceleration. We still do not even know its intrinsic nature, and in investigating its properties we can not exclude the possibility of an interaction between DE and the other components of the Universe. In recent times, a new class of interacting DE models have been proposed in the literature. These assume that the interaction between DE and matter could be well approximated by a pure momentum exchange. The efficiency of the process is then described by the interaction cross section. These models have been investigated via N-body simulations in the case of scattering between DE and dark matter, discovering that the nonlinear effects can be stronger than the linear ones. More recently such scenario has been extended to a scattering between DE and baryons, asking whether it would be possible to detect its effects through cosmological observations. A linear analysis lead to the conclusion that, even for extremely large values of the cross section, the impact of DE-baryon scattering on the CMB power spectrum and the matter power spectrum would be undetectable. Therefore, the only yet unexplored field that leaves an opportunity to put cosmological constraints on such interaction is the nonlinear regime of structure formation, which can be properly studied only through N-body simulations. In this work we modify the GADGET3 code in order to perform, for the first time in the literature, structure formation simulations which implement DE-baryon scattering. We focus on the effects of such interaction on major cosmological observables: the power spectrum, the mass function, the halo density profiles and the halo baryon fraction profiles. We find that the nonlinear effects of DE-baryon scattering can significantly affect these observables, thus paving the way to the future constraining of this interaction with cosmological observations.