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, $\eta$. In particular, superheavy gauge strings with $\eta \sim {10}^{16}\mathrm{GeV}$ are ruled out unless the dilaton mass $m_{\phi }\gtrsim 100\mathrm{TeV}$, while the currently popular value $m_{\phi }\sim 1\mathrm{TeV}$ imposes the bound $\eta \lesssim 3\times {10}^{11}\mathrm{GeV}$. Some nonstandard cosmological scenarios which can avoid these constraints are pointed out.