Prominence: A discriminator of gravitational wave signals

The concept of prominence is familiar to signal engineers, topographers and mountaineers. We introduce Prominence $\mathcal P$ as a discriminator of gravitational wave (GW) signals. We treat black hole and neutron star binaries as astrophysical background sources, and show how $\mathcal P$ can be used to distinguish between GW spectra produced by first-order phase transitions, domain walls and cosmic strings, and combinations thereof. Prominence can also be used to discriminate between these and off-piste sources of GWs. The uncertainty in the measured energy density in GWs at Pulsar Timing Arrays needs to be smaller than $\sim 4\%$ for $\mathcal{P}$ to achieve discrimination at 3$\sigma$. LISA and ET data are expected to have sufficiently small uncertainties that Prominence can play a central role in their analysis.