Lattice QCD Calculation of the Subtraction Function in Forward Compton Amplitude

Journal Article · 19 February 2025 · Physical Review Letters

DOI: https://doi.org/10.1103/physrevlett.134.071903 · OSTI ID:2526227

Fu, Yang  ^[1]; Feng, Xu  ^[2]; Jin, Lu-Chang  ^[3]; Liu, Chuan  ^[2]; Wen, Shi-Da ^[4]

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1. Massachusetts Institute of Technology, Cambridge, MA (United States); Peking University, Beijing (China)
2. Peking University, Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)
3. University of Connecticut, Storrs, CT (United States)
4. Peking University, Beijing (China)

The subtraction function plays a pivotal role in calculations involving the forward Compton amplitude, which is crucial for predicting the Lamb shift in muonic atoms, as well as the proton-neutron mass difference. In this Letter, we present a lattice QCD calculation of the subtraction function using two domain wall fermion gauge ensembles near the physical pion mass. We utilize a recently proposed subtraction point, demonstrating its advantage in mitigating statistical and systematic uncertainties by eliminating the need for ground-state subtraction. Our results reveal significant contributions from N⁢π intermediate states to the subtraction function. Incorporating these contributions, we compute the proton, neutron, and nucleon isovector subtraction functions at photon momentum transfer Q²ϵ[0,2] GeV². For the proton subtraction function, we compare our lattice results with chiral perturbation theory prediction at low Q² and with the results from the perturbative operator-product expansion at high Q². Finally, using these subtraction functions as input, we determine their contribution to two-photon exchange effects in the Lamb shift and isovector nucleon electromagnetic self-energy.

• Research Organization: Massachusetts Institute of Technology, Cambridge, MA (United States)
• Sponsoring Organization: NSFC of China; USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: SC0010339; SC0011090; SC0021147
• OSTI ID: 2526227
• Journal Information: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 7 Vol. 134; ISSN 0031-9007
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English