Can the graviton have non-zero mass?

by Gregory GABADADZE (University of Minnesota)

Thursday 27 Sept 2001, 14:00 → 15:00 Europe/Zurich

TH Auditorium (CERN)

I will address the question whether a graviton could have a small non-zero mass. The issue is subtle for two reasons: first, there is a discontinuity in the mass in the lowest tree-level approximation which implies that the graviton cannot be massive. Second, the non-linear four-dimensional theory of a massive graviton is not defined unambiguously. However, I shall argue that for a vanishing graviton mass the lowest tree-level approximation breaks down. Moreover, non-perturbative solutions are smooth and continuous in the graviton mass. I will discuss a non-linear, generally covariant model which possesses all the crucial properties of massive gravity. The exact cosmological solutions of the model are continuous in the mass, yet the perturbative expansion has a discontinuity in the leading order. The extra helicity-zero graviton state which is responsible for the perturbative discontinuity decouples in the limit of vanishing graviton mass in the full classical theory.