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, $\mu$. The limit due to the millisecond-pulsar constraint is $\mu <4\mathrm{}\times {10}^{-5\mathrm{}}$ ${\mathit{c}}^2$/G while the nucleosynthesis limit ranges from $\mu <6\mathrm{}\times {10}^{-6\mathrm{}}$ ${\mathit{c}}^2$/G to $\mu <2\mathrm{}\times {10}^{-5\mathrm{}}$ ${\mathit{c}}^2$/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 ($\mu <5\mathrm{}\times {10}^{-6\mathrm{}}$ ${\mathit{c}}^2$/G) and are well above the value of $\mu$ that seems to be favored by the string-seeded galaxy-formation scenario.