Parity violation in atoms and radiative corrections to the nuclear weak charge caused by the strong nuclear electric field.

Large atomic measurements of the so-called nuclear weak charge provide an important test of the standard electroweak model and impose constraints on new physics beyond the model. We have found a previously unknown mechanism for correction to the weak charge at the level of 0.5 - 1%. This can substantially influence the comparison between the model and the experiment.

There are now experiments measuring atomic parity violation in bismuth, lead, thallium, and cesium. Analysis of this data provides an important test of the standard electroweak model and impose constraints on new physics beyond the model. It is believed now that the model agrees with the experiment data with an accuracy of about 0.5%. This is a combined experimental and theoretical uncertainty. Many-body theory plays a crucial role in this analysis: it relates the observable values to the fundamental constant, weak charge.

In standard theoretical analysis the effect arises due to the Z-boson exchange between electron and nucleus.

There are also so-called radiative corrections that arise when the Z-boson on its way from the electron to the nucleus virtually excites g - quantum as well as quark-antiquark or lepton-antilepton pairs from the vacuum.

These radiative corrections were taken into account in previous analyses, but they were calculated without account of the nucleus Coulomb field. However the field is very strong, for example at the surface of a cesium nucleus it is about 3 10²¹V/m. We have shown that the field modifies the radiative corrections substantially. The estimate for the modification is about 0.5 - 1% of the observable effect. This modification requires an accurate calculation, but it is already clear that it can substantially influence interpretation of the experimental data.