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Axial vector form factors from lattice QCD that satisfy the PCAC relation
Physical Review Letters ( IF 9.227 ) Pub Date : 
Yong-Chull Jang, Rajan Gupta, Boram Yoon, and Tanmoy Bhattacharya

Previous lattice QCD calculations of axial vector and pseudoscalar form factors show significant deviation from the partially conserved axial current (PCAC) relation between them. Since the original correlation functions satisfy PCAC, the observed deviations from the operator identity cast doubt on whether all the systematics in the extraction of form factors from the correlation functions are under control. We identify the problematic systematic as a missed excited state, whose energy as a function of the momentum transfer squared, Q2, is determined from the analysis of the 3-point functions themselves. Its energy is much smaller than those of the excited states previously considered and including it impacts the extraction of all the ground state matrix elements. The form factors extracted using these mass/energy gaps satisfy PCAC and another consistency condition, and validate the pion-pole dominance hypothesis. We also show that the extraction of the axial charge gA is very sensitive to the value of the mass gaps of the excited states used and current lattice data do not provide an unambiguous determination of these, unlike the Q2≠0 case. To highlight the differences and improvement between the conventional versus the new analysis strategy, we present a comparison of results obtained on a physical pion mass ensemble at a≈0.0871~fm. With the new strategy, we find gA=1.30(6) and axial charge radius $r_A = 0.74(6) $~fm, both extracted using the z-expansion to parameterize the Q2 behavior of GA(Q2), and gP*=8.06(44) obtained using the pion pole-dominance ansatz to fit the Q2 behavior of the induced pseudoscalar form factor G̃P(Q2). These results are consistent with current phenomenological values.
更新日期:2020-01-14

 

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