NUCLEOSYNTHESIS CONSTRAINTS ON COSMIC STRINGS

We reanalyze the nucleosynthesis predictions in the presence of a background of gravitational radiation from string loop decay. The comparison with light elements abundance provides upper bounds on the dimensionless string mass per unit length G-mu. These bounds are stronger than present bounds coming from the millisecond-pulsar timing stability. For N(v) = 3 the nucleosynthesis bounds are consistent with the values required for galaxy formation, provided that alpha < 10(-3) (where alpha is the ratio of the initial size of the loop relative to the horizon size), and are stronger than present bounds coming from the angular distortions in the microwave background radiation. In the limit alpha --> 0 we find G-mu < [2.6 + 12.9(3-N(v))] X 10(-6).