The two faces of mimetic Horndeski gravity: disformal transformations and Lagrange multiplier

摘要: We show that very general scalar-tensor theories of gravity (including, e.g., Horndeski models) are generically invariant under disformal transformations. However there is a special subset, when the transformation not invertible, yields new equations motion which generalization so-called "mimetic" dark matter theory recently introduced by Chamsedinne and Mukhanov. These conclusions hold true irrespective whether scalar field in action assumed same or different than involved transformation. The for our mimetic can also be derived from an containing additional Lagrange multiplier field. has number derivatives as original theory. As application we simplest model able to mimic cosmological background flat FLRW with barotropic perfect fluid any constant equation state.