Gravitational Imprints of Flavor Hierarchies
  The mass hierarchy among the three generations of quarks and charged leptons
is one of the greatest mysteries in particle physics. In various flavor models,
the origin of this phenomenon is attributed to a series of hierarchical
spontaneous symmetry breakings, most of which are beyond the reach of particle
colliders. We point out that the observation of a multi-peaked stochastic
gravitational wave signal from a series of cosmological phase transitions could
well be a unique probe of the mechanism behind flavor hierarchies. To
illustrate this point, we show how near future ground- and space-based
gravitational wave observatories could detect up to three peaks in the recently
proposed $PS^3$ model.
