Dark Energy: Can the Fifth Force be Screened?

Synopsis

The phenomenology of dark energy may be explained by an extra scalar particle mediating a fifth force at cosmological scales. However, stringent limits on the existence of extra forces have been placed by solar-system experiments: viable models must therefore be able to screen (i.e. suppress) the fifth force in environments where it is known to be small. In the first part of the talk, I will present a theoretical test of Vainsthein screening. Progress in tests of this mechanism has been hindered by the complexity of the field equations involved. I will present a numerical approach based on the finite element method that overcomes this problem, and use it to assess whether Vainsthein screening can effectively take place within the limits of validity of the theories that invoke it. In the second part of the talk, I will present an emulator for the large-scale structure in presence of one extra fundamental force. Characterizing the nonlinear scales of the large-scale structure accurately is essential for the goals of the next generation of surveys. However, doing so requires running expensive N-body simulations whose use is impractical in cosmological statistical analyses. Emulators offer a way out of this impasse, by allowing us to obtain the output of an N-body simulation without running it. This opens the way to using them in statistical analyses of large cosmological datasets.