Probing New Physics with Isotope Shift Spectroscopy

We investigate the potential to probe physics beyond the Standard Model withisotope shift measurements of optical atomic clock transitions. We first derivethe reach for generic new physics above the GeV scale at the effective fieldtheory level, as well as estimate the limits on possible new spin-independentforces mediated by sub-GeV states coupled to electrons and neutrons. We alsostudy the weak force and show that isotope shifts could provide strongconstraints on the $Z^0$ couplings to valence quarks, which complementprecision observables at LEP and atomic parity violation experiments. Finally,motivated by recent experimental hints of a new 750 GeV resonance in diphotons,we also consider the potential to probe its parity-preserving couplings toelectrons, quarks and gluons with this method. In particular, combining thediphoton signal with indirect constraints from $g_e-2$ and isotope shifts inYtterbium allows to probe the resonance coupling to electrons withunprecedented precision