Cosmic Strings and the String Dilaton

Abstract

The existence of a dilaton (or moduli) with gravitational-strength coupling to matter imposes stringent constraints on the allowed energy scale of cosmic strings, $\ensuremath{\eta}$. In particular, superheavy gauge strings with $\ensuremath{\eta}\ensuremath{\sim}{10}^{16}\mathrm{GeV}$ are ruled out unless the dilaton mass ${m}_{\ensuremath{\varphi}}\ensuremath{\gtrsim}100\mathrm{TeV}$, while the currently popular value ${m}_{\ensuremath{\varphi}}\ensuremath{\sim}1\mathrm{TeV}$ imposes the bound $\ensuremath{\eta}\ensuremath{\lesssim}3\ifmmode\times\else\texttimes\fi{}{10}^{11}\mathrm{GeV}$. Some nonstandard cosmological scenarios which can avoid these constraints are pointed out.