Theory HEP Seminar

Fate of cosmological solutions in massive gravity

Emir Gumrukcuoglu

IPMU

The construction of a finite-range gravity theory has been one of the major challenges in classical field theory for the last 70 years. Recently, de Rham, Gabadadze and Tolley constructed a nonlinear theory of massive gravity, which successfully removes the unwanted extra degree that contaminated earlier constructions. The theory allows for homogeneous and isotropic solutions with self acceleration, providing an alternative to dark energy. However, the perturbation analysis shows that at linear level, these solutions contain only 2 propagating degrees of freedom, as opposed to 5 expected from a massive spin-2 particle. I will show that at nonlinear order, the additional 3 degrees acquire non-vanishing kinetic terms. For one of these degrees, the sign of the kinetic term is always negative, leading to a ghost instability in the homogeneous and isotropic background. I will conclude by presenting a new anisotropic solution which looks isotropic at the background level. For this solution, the nonlinear ghost which appears in the purely isotropic solution may be evaded.