Informal Pizza Seminar

Binary Pulsar Spin-Down Constraints on Massive Gravity

Claudia de Rham

Perimeter Institute

In models of massive gravity, the additional helicity states of the graviton give rise to light scalar degrees of freedom that evade fifth force experiments due to strong coupling. The gradient of the additional fields being generically very small, it gives rise to a force that is greatly suppressed relative to the usual Newtonian one, hence making predictions which are consistent with solar system tests of gravity. One can show however that, contrary to previous expectations, binary pulsar spin-down observations provide very strong constraints on theories of massive gravity. This is because the energy flux of the zero helicity degrees of freedom of the graviton can be significant even in the region in which these scalars are strongly coupled and forced to have small amplitude. Furthermore, for highly eccentric binary pulsars, the dominant radiation is monopole radiation which enhances its contribution relative to the quadrupole gravitational flux.