Graviton decay via excitation of nonlinear vacuum fluctuations
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Gravitons relate to gravitational waves as photons to electromagnetic waves, but with the important difference that Einstein gravity is intrinsically nonlinear. This could lead in principle to the decay of a graviton into many collinear gravitons of smaller frequency, but such a process is found to have a very small probability. Another possibility is the decay of gravitons by interaction with a class of vacuum fluctuations made of weakly-bound couples of virtual masses. In this case the final state is a continuum of excited and Lorentz-boosted bound states. We estimate the decay probability by evaluating the relevant matrix elements and phase space volume, with a suitable cut-off. The calculation also leads to further insights into the properties of these vacuum fluctuations. We find that the probability of this decay process is also very small, and compatible with the existence of gravitational waves with very long propagation range.