Cosmic Strings and the String Dilaton

The existence of a dilaton (or moduli) with gravitational-strength coupling to matter imposes stringent constraints on the allowed energy scale of cosmic strings, η. In particular, superheavy gauge strings with η~10¹⁶GeV are ruled out unless the dilaton mass m_φ100TeV, while the currently popular value m_φ~1TeV imposes the bound η3×10¹¹GeV. Some nonstandard cosmological scenarios which can avoid these constraints are pointed out.