We argue that massive quantum fields source low-frequency long-wavelength metric fluctuations through the quantum fluctuations of their stress-energy , given reasonable assumptions about the analytic structure of its correlators .
This can be traced back to the non-local nature of the gauge symmetry in General Relativity , which prevents an efficient screening of UV scales ( what we call the cosmological non-constant problem ) .
We define a covariant and gauge-invariant observable which probes line-of-sight spacetime curvature fluctuations on an observer ’ s past lightcone , and show that current pulsar timing data constrains any massive particle to m \lesssim 600 GeV .
This astrophysical bound severely limits the possibilities for physics beyond the standard model below the scale of quantum gravity .