The subtraction contribution to the muonic-hydrogen Lamb shift: a point for lattice QCD calculations of the polarizability effect

Understand

The proton-polarizability contribution to the muonic-hydrogen Lamb shift is a major source of theoretical uncertainty in the extraction of the proton charge radius.

• An empirical evaluation of this effect, based on the proton structure functions, requires a systematically improvable calculation of the "subtraction function", possibly using lattice QCD.
• We consider a different subtraction point, with the aim of accessing the subtraction function directly in lattice calculations.
• A useful feature of this subtraction point is that the corresponding contribution of the structure functions to the Lamb shift is suppressed.