First-Principles Determination of the Proton-Proton Fusion Matrix Element from Lattice QCD
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arXiv
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| Autori principali: | , , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2026
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| _version_ | 1866911517390143488 |
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| author | Wang, Zi-Yu Feng, Xu Jian, Bo-Hao Jin, Lu-Chang Liu, Chuan |
| author_facet | Wang, Zi-Yu Feng, Xu Jian, Bo-Hao Jin, Lu-Chang Liu, Chuan |
| contents | Proton-proton fusion is the fundamental weak reaction initiating stellar energy production, and a first-principles determination of its matrix element remains a long-standing goal of nuclear theory. We present a lattice QCD calculation of the pp fusion matrix element at m_pi~432 MeV. We implement Lellouch-Luscher (LL) finite-volume (FV) corrections within a 2+J->2 framework, accounting for two-nucleon (2N) rescattering, to relate FV matrix elements to infinite-volume counterparts. Excited-state contamination is suppressed using bi-local nucleon-nucleon interpolating operators and a variational analysis with three lowest momenta. This enables determination of 2N energy spectrum and scattering parameters via Luscher's FV formalism. Before including rescattering effects in the LL factor, we obtain <d|J|pp>/g_A = 0.984(10), where g_A is the axial charge. The deviation from unity indicates a small nonvanishing 2-body current contribution. Our analysis shows that rescattering effects in LL factors substantially modify the 2-body contribution, while large uncertainties in 2N scattering parameters propagate strongly into FV corrections. Thus, precise determination of the 2-body low-energy constant L_{1,A} remains highly challenging with current lattice inputs. Despite the large uncertainty, L_{1,A}=6.0(7.1) fm^3 is compatible, at the level of naturalness, with phenomenological extractions. This work demonstrates feasibility and intrinsic challenges of ab initio lattice QCD calculations of weak 2N reactions, and establishes a foundation for future studies at or near the physical pion mass. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_09554 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | First-Principles Determination of the Proton-Proton Fusion Matrix Element from Lattice QCD Wang, Zi-Yu Feng, Xu Jian, Bo-Hao Jin, Lu-Chang Liu, Chuan High Energy Physics - Lattice Proton-proton fusion is the fundamental weak reaction initiating stellar energy production, and a first-principles determination of its matrix element remains a long-standing goal of nuclear theory. We present a lattice QCD calculation of the pp fusion matrix element at m_pi~432 MeV. We implement Lellouch-Luscher (LL) finite-volume (FV) corrections within a 2+J->2 framework, accounting for two-nucleon (2N) rescattering, to relate FV matrix elements to infinite-volume counterparts. Excited-state contamination is suppressed using bi-local nucleon-nucleon interpolating operators and a variational analysis with three lowest momenta. This enables determination of 2N energy spectrum and scattering parameters via Luscher's FV formalism. Before including rescattering effects in the LL factor, we obtain <d|J|pp>/g_A = 0.984(10), where g_A is the axial charge. The deviation from unity indicates a small nonvanishing 2-body current contribution. Our analysis shows that rescattering effects in LL factors substantially modify the 2-body contribution, while large uncertainties in 2N scattering parameters propagate strongly into FV corrections. Thus, precise determination of the 2-body low-energy constant L_{1,A} remains highly challenging with current lattice inputs. Despite the large uncertainty, L_{1,A}=6.0(7.1) fm^3 is compatible, at the level of naturalness, with phenomenological extractions. This work demonstrates feasibility and intrinsic challenges of ab initio lattice QCD calculations of weak 2N reactions, and establishes a foundation for future studies at or near the physical pion mass. |
| title | First-Principles Determination of the Proton-Proton Fusion Matrix Element from Lattice QCD |
| topic | High Energy Physics - Lattice |
| url | https://arxiv.org/abs/2603.09554 |