Volume 430 - The 39th International Symposium on Lattice Field Theory (LATTICE2022) - Hadron Structure
Nucleon form factors and the pion-nucleon sigma term
R. Gupta*, T. Bhattacharya, V. Cirigliano, M. Hoferichter, Y.C. Jang, B. Joo, E. Mereghetti, S. Mondal, S. Park, F. Winter and B. Yoon
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Abstract
This talk summarizes the progress made since Lattice 2021 in
understanding and controlling the contributions of towers of multihadron excited states with mass gaps starting lower than of radial excitations, and in increasing our confidence in the extraction of ground state nucleon matrix elements. The most clear evidence for multihadron excited state contributions (ESC) is in axial/pseudoscalar form factors that are required to satisfy the PCAC relation between them. The talk examines the broader question--which and how many of the theoretically allowed positive parity states $N(\textbf p)\pi(-\textbf p)$, $N(\textbf 0)\pi(\textbf 0)\pi(\textbf 0)$, $N(\textbf p)\pi(\textbf 0)$, $N(\textbf 0)\pi(\textbf p),\ \ldots$ make significant contributions to a given matrix element? New data for the axial, electric and magnetic form factors are presented. They continue to show trends observed in Ref.[1]. The N${}^2$LO $\chi$PT analysis of the ESC to the pion-nucleon sigma term, $\sigma_{\pi N}$, has been extended to include the $\Delta$ as an explicit degree of freedom [2]. The conclusion reached in Ref.[3] that $N \pi$ and $N \pi \pi$ states each contribute about 10 MeV to $\sigma_{\pi N}$, and the consistency between the lattice result with $N \pi$ state included and the phenomenological estimate is not changed with this improvement.
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