Nucleon form factors and moments of generalized parton distributions usingNf=2+1+1twisted mass fermions

Abstract

We present results on the axial and the electromagnetic form factors of the nucleon, as well as, on the first moments of the nucleon generalized parton distributions using maximally twisted mass fermions. We analyze two N f =2+1+1 ensembles having pion masses of 213 MeV and 373 MeV each at a different value of the lattice spacing. The lattice scale is determined using the nucleon mass computed on a total of 17 N f =2+1+1 ensembles generated at three values of the lattice spacing, a. The renormalization constants are evaluated non-perturbatively with a perturbative subtraction of O(a 2 )-terms. The moments of the generalized parton distributions are given in the MS scheme at a scale of µ = 2 GeV. We compare with recent results obtained using different discretization schemes. The implications on the spin content of the nucleon are also discussed.

Stochastic method with low mode substitution for nucleon isovector matrix elements

“…This value is similar to those from most lattice calculations [3,7,[13][14][15] and is larger than the experimental value. However, the O(a 2 ) error has not been considered.…”

“…Most attempts have resulted in values ∼10% below the experimental number for the axial-vector coupling [1][2][3][4][5][6][7][8], while a few claim that their results could be consistent with experiment [9][10][11][12]. For the quark momentum fraction x u−d , overestimation by ∼20 -30% is common in most of the calculations [3,7,[13][14][15] except [8].…”

“…In Sec. V, the results of isovector matrix elements of the nucleon for the axialvector g 3 A , the scalar coupling g 3 S and the quark momentum fraction x u−d are provided. A short summary and outlook are presented in Sec.…”

“…For the quark momentum fraction x u−d , overestimation by ∼20 -30% is common in most of the calculations [3,7,[13][14][15] except [8].…”

Disconnected contributions to the spin of the nucleon

“…For recent numerical investigations of the nucleon spin, and related matrix elements, see Refs. [8][9][10][11][12][13][14][15][16].…”