Showing 1–2 of 2 results for author: Schar, T

Gross-Llewellyn Smith sum rule from lattice QCD

Authors: K. Utku Can, Joshua A. Crawford, Roger Horsley, Paul E. L. Rakow, Thomas G. Schar, Gerrit Schierholz, Hinnerk Stüben, Ross D. Young, James M. Zanotti

Abstract: We compute the Gross-Llewellyn Smith sum rule, i.e. the lowest odd moment of the parity-violating structure function, $F_3$, of the nucleon from a lattice QCD calculation of the Compton amplitude. Our calculations are performed on $48^3 \times 96$ lattices at the $SU(3)$ symmetric point for two lattice spacings. We extract the moments for several values of the current momenta in the range… ▽ More We compute the Gross-Llewellyn Smith sum rule, i.e. the lowest odd moment of the parity-violating structure function, $F_3$, of the nucleon from a lattice QCD calculation of the Compton amplitude. Our calculations are performed on $48^3 \times 96$ lattices at the $SU(3)$ symmetric point for two lattice spacings. We extract the moments for several values of the current momenta in the range $0.5 \lesssim Q^2 \lesssim 10 \; {\rm GeV}^2$, covering both the nonperturbative and perturbative regimes. We compare our moments to the Gross-Llewellyn Smith sum rule and discuss the implications for higher-twist effects, a determination of $α_s(Q^2)$ from a hadronic quantity complementing the phenomenological and other lattice approaches, and electroweak box contributions crucial for Cabibbo-Kobayashi-Maskawa matrix unitarity studies. △ Less

Submitted 11 June, 2025; v1 submitted 26 February, 2025; originally announced February 2025.

Comments: 16 pages, 12 figures

Report number: ADP-25-6/T1268, DESY-25-019, LTH 1394

Journal ref: Phys.Rev.D 111 (2025) 11, 114505

Lattice QCD calculation of the Compton amplitude subtraction function

Authors: K. U. Can, A. Hannaford-Gunn, R. Horsley, P. E. L. Rakow, T. Schar, G. Schierholz, H. Stüben, R. D. Young, J. M. Zanotti

Abstract: The Compton amplitude subtraction function is an essential component in work concerning both the proton radius puzzle and the proton-neutron mass difference. However, owing to the difficulty in determining the subtraction function, it remains a key source of uncertainty in these two contexts. Here, we use the Feynman-Hellmann method to determine this subtraction function directly from lattice QCD.… ▽ More The Compton amplitude subtraction function is an essential component in work concerning both the proton radius puzzle and the proton-neutron mass difference. However, owing to the difficulty in determining the subtraction function, it remains a key source of uncertainty in these two contexts. Here, we use the Feynman-Hellmann method to determine this subtraction function directly from lattice QCD. Furthermore, we demonstrate how to control dominant discretisation artefacts for this calculation, eliminating a major source of systematic error. This calculation is performed for a range of hard momentum scales, and three different sets of gauge configurations for pion masses about 400 MeV. Our results show good agreement with continuum OPE expectations. As such, this work paves the way for model-independent and precise determinations of the subtraction function over a wide range of kinematics. △ Less

Submitted 21 May, 2025; v1 submitted 15 January, 2025; originally announced January 2025.

Comments: 15 pages, 8 figures. Version accepted for publication in Phys. Rev. D

Report number: ADP-24-23/T1262, DESY-24-221, Liverpool LTH 1390

Journal ref: Phys. Rev. D. 111, 094513 (2025)