Gravitational Waves from First-Order Phase Transitions: LIGO as a Window
  to Unexplored Seesaw Scales
  Within a recently proposed classically conformal model, in which the
generation of neutrino masses is linked to spontaneous scale symmetry breaking,
we investigate the associated phase transition and find it to be of strong
first order with a substantial amount of supercooling. Carefully taking into
account the vacuum energy of the metastable minimum, we demonstrate that a
significant fraction of the model's parameter space can be excluded simply
because the phase transition cannot complete. We argue this to be a powerful
consistency check applicable to general theories based on classical scale
invariance. Finally, we show that all remaining parameter points predict a
sizable gravitational wave signal, so that the model can be fully tested by
future gravitational wave observatories. In particular, most of the parameter
space can already be probed by the upcoming LIGO science run starting in early
2019.
