The two-body potential of Vainshtein screened theories
  Adding a light scalar degree of freedom to General Relativity often induces a
fifth force whose magnitude is strongly constrained by laboratory experiments
and solar system tests. The Vainshtein screening mechanism ensures that the
effects of this supplementary force are suppressed in dense environments.
However, the field solution of theories exhibiting Vainshtein screening is only
known in spherically symmetric situations. In this article we examine in
different configurations the two-body potential energy of pointlike particles
in a specific $P(X)$ theory with Vainshtein screening. We use ideas borrowed
from the Effective One-Body approach of Buonanno and Damour in order to
restrict the form of the solution. Our results indicate that, even if
Vainshtein screening is also fully active in the equal-mass case, the nonlinear
dependance of the two-body energy on the mass ratio implies a violation of the
Equivalence Principle. We compute the contribution of this effect to the Moon
orbit for generic theories equipped with Vainshtein screening.
