QED Theory of the Nuclear Recoil with Finite Size

We investigate the modification of the transverse electromagnetic interaction between two pointlike particles when one particle acquires a finite size. It is shown that the correct treatment of such interaction cannot be accomplished within the Breit approximation but should be addressed within the QED. The complete QED formula is derived for the finite-size nuclear recoil, exact in the coupling strength parameter Z alpha. Numerical calculations are carried out for a wide range of Z and verified against the oZ alpha thorn 5 contribution. The comparison with the Z alpha expansion identifies the contribution of order oZ alpha thorn 6, which is linear in the nuclear radius and numerically dominates over the lower-order oZ alpha thorn 5 term.

Automated summary

This study examines how the transverse electromagnetic interaction between two pointlike particles is modified when one of the particles has a finite size. It is found that the traditional Breit approximation is not sufficient, and the interaction should be treated within the framework of Quantum Electrodynamics (QED). The complete QED formula for the finite-size nuclear recoil is derived, taking into account the coupling strength parameter Z alpha. Numerical calculations are performed for a range of Z values and validated against the oZ alpha thorn 5 contribution. Comparison with the Z alpha expansion reveals the significance of the oZ alpha thorn 6 term, which is linear in the nuclear radius and numerically dominates over the lower-order oZ alpha thorn 5 term.