Speaker
Description
We study the effect of an ultra-light primordial black hole (PBH) dominated phase on the
gravitational wave (GW) spectrum generated by a cosmic string (CS) network formed as a result
of a high-scale U(1) symmetry breaking. A PBH-dominated phase leads to tilts in the spectrum
via entropy dilution and generates a new GW spectrum from PBH density fluctuations, detectable
at ongoing and planned near-future GW detectors. The combined spectrum has a unique shape
with a plateau, a sharp tilted peak over the plateau, and a characteristic fall-off, which can be
distinguished from the one generated in the combination of CS and any other matter domination
or new exotic physics. We discuss how ongoing and planned future experiments can probe such
a unique spectrum for different values of U(1) breaking scale and PBH parameters such as initial
mass and energy fraction.
