Equivalence principle violations and couplings of a light dilaton

We consider possible violations of the equivalence principle through the exchange of a light “dilaton-like” scalar field. Using recent work on the quark-mass dependence of nuclear binding, we find that the dilaton-quark-mass coupling induces significant equivalence-principle-violating effects varying like the inverse cubic root of the atomic number—$A^{-1/3}$. We provide a general parametrization of the scalar couplings, but argue that two parameters are likely to dominate the equivalence-principle phenomenology. We indicate the implications of this framework for comparing the sensitivities of current and planned experimental tests of the equivalence principle.

Figure 1

The value of the scalar strength ${\eta }_S$ as a function of the pion mass.