title: Spontaneous lorentz breaking and massive gravity.
abstract: Theories with an extra spin-two field coupled to gravity admit a massive phase with broken Lorentz symmetry. While the equivalence principle is respected, the Newtonian potentials are in general modified, but they may be protected by a scale symmetry of the coupling term. The gravitational waves phenomenology is quite rich: two gravitons, one massive and one massless, oscillate and propagate with distinct velocities, different from the speed of light. A time of flight difference between gravitons and photons from a common source would provide a clear signal of this theory.
authors.affiliation: Dipartimento di Fisica, Università di L'Aquila and INFN-LNGS, I-67010 L'Aquila, Italy.
authors.forename: Z
authors.initials: Z
authors.lastname: Berezhiani
authors.forename: D
authors.initials: D
authors.lastname: Comelli
authors.forename: F
authors.initials: F
authors.lastname: Nesti
authors.forename: L
authors.initials: L
authors.lastname: Pilo