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

TL;DR

This paper presents a novel lattice QCD method to calculate the two-photon exchange contribution to the muonic-hydrogen Lamb shift, successfully demonstrating its feasibility with results consistent with previous theoretical estimates.

Contribution

It introduces a new lattice QCD approach for computing the two-photon exchange contribution to the Lamb shift in muonic hydrogen, including the first such calculation at near-physical pion mass.

Findings

Calculated the two-photon exchange contribution as approximately 37.4 μeV.

Demonstrated the feasibility of lattice QCD for this calculation.

Results agree with previous theoretical estimates within uncertainties.

Abstract

We develop a method for lattice QCD calculation of the two-photon exchange contribution to the muonic-hydrogen Lamb shift. To demonstrate its feasibility, we present the first lattice calculation with a gauge ensemble at $m_\pi = 142$ MeV. By adopting the infinite-volume reconstruction method along with an optimized subtraction scheme, we obtain $\Delta E_{\text{TPE}} = -28.9(4.9)~\mu\text{eV} + 93.72~\mu\text{eV}/\text{fm}^2 \cdot\langle r_p^2 \rangle$, or $\Delta E_{\text{TPE}} = 37.4(4.9)~\mu$eV, which is consistent with the previous theoretical results in a range of 20-50 $\mu$eV.