New limits on cosmic strings from gravitational wave observation

Understand

We combine new analysis of the stochastic gravitational wave background to be expected from cosmic strings with the latest pulsar timing array (PTA) limits to give an upper bound on the energy scale of the possible cosmic string network, $G\mu < 1.5\times 10^{-11}$ at the 95% confidence level.

• We also show bounds from LIGO and to be expected from LISA and BBO.
• Current estimates for the gravitational wave background from supermassive black hole binaries are at the level where a PTA detection is expected.
• But if PTAs do observe a background soon, it will be difficult in the short term to distinguish black holes from cosmic strings as the source, because the spectral indices from the two sources happen to be quite similar.