Nucleon form factors in dispersively improved chiral effective field theory: Scalar form factor
We propose a method for calculating the nucleon form factors (FFs) of $G$parityeven operators by combining Chiral Effective Field Theory ($$\chi$$EFT) and dispersion analysis. The FFs are expressed as dispersive integrals over the twopion cut at $$t > 4 M_\pi^2$$. The spectral functions are obtained from the elastic unitarity condition and expressed as products of the complex $$\pi\pi \rightarrow N\bar N$$ partialwave amplitudes and the timelike pion FF. $$\chi$$EFT is used to calculate the ratio of the partialwave amplitudes and the pion FF, which is real and free of $$\pi\pi$$ rescattering in the $t$channel ($N/D$ method). The rescattering effects are then incorporated by multiplying with the squared modulus of the empirical pion FF. The procedure results in a marked improvement compared to conventional $$\chi$$EFT calculations of the spectral functions. We apply the method to the nucleon scalar FF and compute the scalar spectral function, the scalar radius, the $t$dependent FF, and the ChengDashen discrepancy. Higherorder chiral corrections are estimated through the $$\pi N$$ lowenergy constants. Results are in excellent agreement with dispersiontheoretical calculations. We elaborate several other interesting aspects of our method. The results show proper scaling behavior in the large$$N_c$$ limit of QCD because the $$\chi$$EFT includes $N$ and $$\Delta$$ intermediate states. The squared modulus of the timelike pion FF required by our method can be extracted from Lattice QCD calculations of vacuum correlation functions of the operator at large Euclidean distances. Our method can be applied to the nucleon FFs of other operators of interest, such as the isovectorvector current, the energymomentum tensor, and twist2 QCD operators (moments of generalized parton distributions).
 Authors:

^{[1]};
^{[1]}
 Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
 Publication Date:
 Report Number(s):
 JLABTHY172525; DOE/OR/231774275; arXiv:1707.07682
Journal ID: ISSN 24699985; PRVCAN
 Grant/Contract Number:
 AC0506OR23177; FPA201677313P
 Type:
 Accepted Manuscript
 Journal Name:
 Physical Review C
 Additional Journal Information:
 Journal Volume: 96; Journal Issue: 5; Journal ID: ISSN 24699985
 Publisher:
 American Physical Society (APS)
 Research Org:
 Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
 Sponsoring Org:
 USDOE Office of Science (SC), Nuclear Physics (NP) (SC26)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; Form factors; dispersion relations; chiral effective field theory; scalar operators; 1=Nc expansion
 OSTI Identifier:
 1410288
 Alternate Identifier(s):
 OSTI ID: 1409461