Excited states and precision results for nucleon charges and form factors

Rajan Gupta, Tanmoy Bhattacharya, Vincenzo Cirigliano, Martin Hoferichter, Yong Chull Jang, Balint Joo, Emanuele Mereghetti, Santanu Mondal, Sungwoo Park, Frank Winter, Boram Yoon

Research output: Contribution to journalConference articlepeer-review

Abstract

The exponentially falling signal-to-noise ratio in all nucleon correlation functions, and the presence of towers of multihadron excited states with relatively small mass gaps makes extraction of matrix elements of various operators within the ground state nucleon challenging. Theoretically, the allowed positive parity states with the smallest mass gaps are the N(p)π(− p), N(0)π(0)π(0), N(p)π(0), N(0)π(p),..., states. A priori, the contribution of these states arises at one loop in chiral perturbation theory (χPT), however, in many cases the contributions are enhanced. In this talk, I will review four such cases: the correlation functions from which the axial form factors, electric and magnetic form factors, the Θ-term contribution to neutron electric dipole moment (nEDM), and the pion-nucleon sigma term are extracted. Including appropriate multihadron states in the analysis can lead to significantly different results compared to standard analyses with the mass gaps taken from fits to 2-point functions. The χPT case for Nπ states is the most clear in the axial/pseudoscalar form factors which need to satisfy the PCAC relation between them. Our analyses, supported by χPT, suggests similarly large effects in the calculations of the Θ-term and the pion-nucleon sigma term that have significant phenomenological implications.

Original languageEnglish
Article number478
JournalProceedings of Science
Volume396
StatePublished - Jul 8 2022
Event38th International Symposium on Lattice Field Theory, LATTICE 2021 - Virtual, Online, United States
Duration: Jul 26 2021Jul 30 2021

Funding

The calculations presented are based on two sets of ensembles: the 2 + 1 + 1-flavor HISQ ensembles generated by the MILC collaboration and the 2 + 1-flavor Wilson-clover ensembles generated by the JLAB/W&M/LANL/MIT collaborations. The calculations used the Chroma software suite [27]. We gratefully acknowledge computing resources provided by NERSC, OLCF at Oak Ridge, USQCD and LANL Institutional Computing. Support for this work was provided the U.S. DOE Office of Science HEP and NP, the SNSF, and by the LANL LDRD program.

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