Millisecond-pulsar constraint on cosmic strings

We study the gravity-wave background produced by a network of cosmic strings using high-resolution numerical simulations of string evolution. Our simulations show that the spectrum of loops produced by the network is dominated by the smallest loops that we can resolve. This reduces the amplitude of the gravity-wave background compared to previous estimates. Reasonable assumptions about how the string network will behave on scales that we cannot resolve indicate that strings with a mass per unit length of μ<4×10^-6c²/G are consistent with the most recent limits on the gravity-wave background that come from millisecond-pulsar timing measurements.