Couplings of a Light Dilaton and Violations of the Equivalence Principle

Experimental discovery of the dilaton would provide strong evidence for string theory. A light dilaton could show up in current tests of the inverse square law for gravity at sub-millimeter distances. In the large extra dimension scenario, Kaluza-Klein excitations of the dilaton can also contribute to the cooling of supernovae. In order to quantify these effects we compute the couplings of a low energy dilaton to matter. These predominantly arise from the fundamental dilaton coupling to the gluon field strength, which receives a sizable enhancement from QCD scaling. We show that detection of the dilaton will give a direct measurement of the QCD coupling constant at the string scale. Particular attention is paid to the size of equivalence principle violating dilaton couplings.