Modified Gravity via Spontaneous Symmetry Breaking

We construct effective field theories in which gravity is modified viaspontaneous breaking of local Lorentz invariance. This is a gravitationalanalogue of the Higgs mechanism. These theories possess additional gravitonmodes and modified dispersion relations. They are manifestly well-behaved inthe UV and free of discontinuities of the van Dam-Veltman-Zakharov type,ensuring compatibility with standard tests of gravity. They may have importantphenomenological effects on large distance scales, offering an alternative todark energy. For the case in which the symmetry is broken by a vector fieldwith the wrong sign mass term, we identify four massless graviton modes (allwith positive-definite norm for a suitable choice of a parameter) and show theabsence of the discontinuity.Comment: 5 pages; revised versio