**Cosmology in nonlinear massive gravity**

**A. Emir Gümrükçüoğlu**

**Kavli IPMU, University of Tokyo**

**06-09-2012 Perşembe/Thursday 15:00**

Özet/Abstract : General theory of relativity, in which the interactions have an infinite range, is in agreement with current experimental and observational data. On the other hand, from a theorist’s point of view, it is an interesting question whether the range of gravity can be consistently made to be finite, or equivalently, whether graviton can have a non-zero mass. This has been one of the most persistent 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 avoids the complications encountered before. 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 background have an interesting behaviour: 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.

Yer : MSGSÜ Bomonti Binası, Fizik Bölümü.

Tarih : 6 Eylül 2012 Perşembe, 15:00