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- Homogeneous and Isotropic Universe from Nonlinear Massive Gravity

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12100002

The question of finite range gravity, or equivalently,

whether graviton can have a non-zero mass, has been one of the major challenges

in classical field theory for the last 70 years.

Generically, a massive gravity theory contains an extra

degree in addition to the 5 polarizations of massive graviton, which turns out

to be a ghost. Recently, de Rham, Gabadadze and Tolley constructed a nonlinear

theory of massive gravity, which successfully eliminates the ghost. Moreover,

the theory has also phenomenological relevance, since the graviton mass may

account for the accelerated expansion of the present universe, providing an

alternative to dark energy. I will present self-accelerating cosmological

solutions in the framework of this theory. The cosmological perturbations

around these backgrounds have an interesting behavior: instead of the 5 degrees

of freedom expected from a massive spin-2 field, only the 2 gravity wave

polarizations are dynamical, at linear level. However, nonlinear analysis of

the extra modes reveal the existence of ghost instabilities. This implies that

a consistent universe solution in this theory should be inhomogeneous and/or

anisotropic.

©2012 Perimeter Institute for Theoretical Physics