Lattice QCD calculation of the two-photon exchange contribution to the muonic-hydrogen Lamb shift

Abstract

We develop a method for lattice QCD calculation of the two-photon exchange (TPE) contribution to the muonic-hydrogen Lamb shift. To demonstrate the feasibility of this method, We also present an exploratory study with a gauge ensemble at 𝑚 𝜋 = 142 MeV. By adopting the infinite-volume reconstruction (IVR) method along with an optimized subtraction scheme, we obtain a preliminary result of the TPE contribution which agrees well with previous calculation using other methods and one magnitude smaller compare to the large ∼ 300 𝜇eV discrepancy for the proton radius puzzle.