Constraints on the gravity-wave background generated by cosmic strings

We investigate the limits that can be placed on a cosmic-string-generated stochastic gravity-wave background by timing of the millisecond pulsar and by primordial nucleosynthesis. These limits on the gravity-wave background are used to generate limits on the mass per unit length of the cosmic string, μ. The limit due to the millisecond-pulsar constraint is μ<4×10^-5 c²/G while the nucleosynthesis limit ranges from μ<6×10^-6 c²/G to μ<2×10^-5 c²/G depending on the history of the Universe at temperatures above 1 TeV and the details of the QCD phase transition. These limits are significantly weaker than the best limit obtained from observations of the microwave background (μ<5×10^-6 c²/G) and are well above the value of μ that seems to be favored by the string-seeded galaxy-formation scenario.