Khronometric theories of modified Newtonian dynamics

In 2011 Blanchet and Marsat suggested a fully relativistic version of Milgrom’s modified Newtonian dynamics (MOND) in which the dynamical degrees of freedom consist of the spacetime metric and a foliation of spacetime, the khronon field. This theory is simpler than the alternative relativsitic formulations. We show that the theory has a consistent non-relativistic or slow motion limit. Blanchet and Marsat showed that in the slow motion limit the theory reproduces stationary solutions of modified Newtonian dynamics. We show that these solutions are stable to khronon perturbations in the low acceleration regime, for the cases of spherical, cylindrical and planar symmetry. For non-stationary systems in the low acceleration regime we show that the khronon field generally gives an order unity correction to the modified Newtonian dynamics.