Fifth-force search with the bound-electron g factor

The use of high-precision measurements of the g factor of few-electron ions and its isotope shifts is put forward as a probe for physics beyond the Standard Model. The contribution of a hypothetical fifth fundamental force to the g factor is calculated for the ground state of H-like, Li-like and B-like ions, and employed to derive bounds on the parameters of that force. The weighted difference and especially the isotope shift of g factors are used in order to increase the experimental sensitivity to the new physics contribution. It is found that, combining measurements from four different isotopes of H-like, Li-like and B-like calcium ions at accuracy levels projected to be accessible in the near future, experimental results compatible with King planarity would constrain the new physics coupling constant more than one order of magnitude further than the best current atomic data and theory. (C) 2020 The Authors. Published by Elsevier B.V.