Testing Super-Heavy Dark Matter from Primordial Black Holes with Gravitational Waves

Understand

Ultra-light primordial black holes with masses $M_{BH}<10^9$~g evaporate before big-bang nucleosynthesis producing all matter fields, including dark matter, in particular super-heavy dark matter: $M_{DM}\gtrsim 10^{10}$ GeV.

• If the dark matter gets its mass via $U(1)$ symmetry-breaking, the phase transition that gives a mass to the dark matter also produces cosmic strings which radiate gravitational waves.
• Because the symmetry-breaking scale $\Lambda_{CS}$ is of the same order as $M_{DM}$, the gravitational waves radiated by the cosmic strings have a large enough amplitude to be detectable across all frequencies accessible with current and planned experimental facilities.
• Moreover, an epoch of early primordial black hole domination introduces a unique spectral break in the gravitational wave spectrum whose frequency is related to the super-heavy dark matter mass.