Nucleosynthesis and the Time Dependence of Fundamental Couplings
  We consider the effects of the time dependence of couplings due to their dependence on a dilaton field, as occurs in superstring theory, as well as in gravity theories of the Jordan-Brans-Dicke type. Because the scale parameters of couplings set by dimensional transmutation depend exponentially on the dilaton vev, we may obtain stringent limits on the shift of the dilaton from the requirement that the induced shift in the couplings not vitiate the successful calculations of element abundances for big-bang nucleosynthesis. These limits can be substantially stronger than those obtained directly from the dilaton-induced change in the gravitational coupling. 
Bruce A. Campbell and Keith A. Olive