Galileon as a local modification of gravity

摘要: In the Dvali-Gabadadze-Porrati (DGP) model, "self-accelerating" solution is plagued by a ghost instability, which makes untenable. This fact, as well all interesting departures from general relativity (GR), are fully captured four-dimensional effective Lagrangian, valid at distances smaller than present Hubble scale. The 4D theory involves relativistic scalar pi, universally coupled to matter and with peculiar derivative self-interactions. this paper, we study connection between self-acceleration presence of ghosts for quite generic class theories that modify gravity in infrared. These defined those shorter cosmological, reduce certain generalization DGP theory. We argue infrared modifications GR locally due scalar, our only one allows robust implementation Vainshtein effect-the decoupling gravitationally bound systems-necessary recover agreement solar-system tests. Our an internal Galilean invariance, under pi's gradient shifts constant. symmetry constrains structure pi Lagrangian so much there exist five terms can yield sizable nonlinearities without introducing ghosts. show such fact de Sitter solutions no ghostlike instabilities. compact sources, these support spherically symmetric, Vainshtein-like nonlinear perturbations also stable against small fluctuations. investigate possible completion scales order horizon, larger. There however some features may constitute problem theoretical or phenomenological level: superluminal excitations; extreme subluminality other excitations, quasistatic approximation observables unreliable Cherenkov emission; very low strong-interaction scale scatterings.