Constraints on Massive-Graviton Dark Matter from Pulsar Timing and Precision Astrometry

The effect of a narrow-band isotropic stochastic gravitational wave background on pulsar timing and astrometric measurements is studied. Such a background appears in some theories of gravity. We show that the existing millisecond pulsar timing accuracy (similar to 0.2 mu s) strongly constrains possible observational consequences of theory of massive gravity with spontaneous Lorentz braking, essentially ruling out significant contribution of massive gravitons to the local dark halo density. The present-day accuracy of astrometrical measurements (similar to 100 mu arc sec) sets less stringent constraints on this theory.