Standard model O(a) renormalization of gA and its impact on new physics searches

We present an O(a) Standard Model calculation of the inner radiative corrections to Gamow-Teller beta decays. We find that a priori contributions arise from the photonic vertex correction and gamma W box diagram. Upon evaluation most elastic contributions vanish due to crossing symmetry or cancellation between isoscalar and isovector photonic contributions, leaving only the polarized parity-odd contribution, i.e., the Gamow-Teller equivalent of the well-known axial gamma W box contribution for Fermi decays. We show that weak magnetism contributes significantly to the Born amplitude, and consider additional hadronic contributions at low energy using a holomorphic continuation of the polarized Bjorken sum rule constrained by experimental data. We perform the same procedure for the Fermi inner radiative correction through a combination of the running of Bjorken and Gross-Llewellyn Smith sum rules. We discuss heavy flavor, higher-twist, and target mass corrections and find a significant increase at low momentum from the latter. We find Delta(A)(R) = 0.02532(22) and Delta(V)(R) = 0.02473(27) for axial and vector inner radiative corrections, respectively, resulting in Delta(A)(R) - Delta(V)(R) = 0.60(5) x 10(-3), which allows us to extract g(A)(0) for the first time to our knowledge. We discuss consequences for comparing experimental data to lattice calculations in beyond Standard Model fits. Further, we show how some traditional beta decay calculations contain part of this effect but fail to account for cancellations in the full O(a) result. Finally, we correct for a double-counting instance in the isospin T = 1/2 mirror decay extraction of vertical bar V-ud vertical bar, the up-down matrix element of the Cabibbo-Kobayashi-Maskawa matrix element, resolving a long-standing tension and leading to increased precision.

Automated summary

This paper presents an O(a) Standard Model calculation for inner radiative corrections to Gamow-Teller beta decays, discussing various contributions such as weak magnetism, hadronic contributions, and corrections at low energy. Results for axial and vector inner radiative corrections are provided, allowing for the extraction of g(A)(0) for the first time. Additionally, corrections for a double-counting instance in mirror decay extraction and implications for comparing experimental data to lattice calculations are discussed.