Fermion-Selective Tests of New Physics with the Bound-Electron g Factor

The use of high-precision measurements of the g factor of single-electron ions is considered as a detailed probe for physics beyond the standard model. The contribution of the exchange of a hypothetical force-carrying scalar boson to the g factor is calculated for the ground state of H-like ions and used to derive bounds on the parameters of that force. Similarly to the isotope shift, we employ the nuclide shift, i.e., the difference for elements with different proton and/or neutron numbers, in order to increase the experimental sensitivity to the new physics contribution. In particular we find, combining available measurements with current precision with different ions, that the coupling constant for the interaction between an electron and a proton can be constrained up to 3 orders of magnitude better than with the best current atomic data and theory.