Speaker
Description
Precision measurements of atomic parity violation and parity-violating electron scattering provide sensitive tests of the Standard Model at low energies. In this work, we show that exchange of two neutrinos, together with analogous fermion-loop contributions, generates a parity-violating dispersion interaction between atomic electrons and quarks. Although the long-range potential scales as $G_F^2/r^5$, its singular short-distance behaviour produces a finite correction of order $G_F^2M_Z^2\sim \alpha G_F$, comparable to conventional electroweak radiative corrections.
We calculate the resulting modification of nuclear weak charges and show that loops of neutrinos, charged leptons, and quarks lighter than the $Z$ boson give a significant enhancement. For medium and heavy atoms the correction is approximately −0.8%. In cesium, this shift is larger than the present experimental uncertainty and brings the Standard Model prediction for the parity-violating amplitude into agreement with experiment. The same mechanism also produces a few-percent correction to the proton weak charge, relevant for parity-violating electron–proton scattering.
These results show that neutrino-mediated dispersion parity violation is an important Standard Model effect for interpreting precision weak-charge measurements and for constraining possible new physics.