Holographic estimate of the meson cloud contribution to nucleon axial form factor

We use light-front holography to estimate the valence quark and the meson cloud contributions to the nucleon axial form factor. The free couplings of the holographic model are determined by the empirical data and by the information extracted from lattice QCD. The holographic model provides a good description of the empirical data when we consider a meson cloud mixture of about 30% in the physical nucleon state. The estimate of the valence quark contribution to the nucleon axial form factor compares well with the lattice QCD data for small pion masses. Our estimate of the meson cloud contribution to the nucleon axial form factor has a slower falloff with the square momentum transfer compared to typical estimates from quark models with meson cloud dressing.

Figure 1

Experimental parametrization of the data $G_A^{\exp }$ according to Eq. (2.2), at red, combined with the estimate of the contribution $Z_N{G}_A^{\mathrm{B}}$ extracted from the lattice QCD data, at blue. The short-dashed-line indicates the central value of Eq. (2.2).

Figure 2

Results of the fit of the axial form factor $G_A$ using $g_A^0=1.2$. The solid-line represent the function $G_A$, the dashed-line represent the bare contribution, $c_3{G}_A^{\mathrm{B}}$, and the dotted-line meson cloud contribution, $c_5{G}_M^{\mathrm{MC}}$. The red and blue bands have the same meaning of Fig. 1.

Figure 3

Comparison of the holographic models (full result) with the lattice QCD data [60, 61]. The models are labeled with the value of $g_A^0$ presented in Table 1.

Figure 4

Comparison of $G_A^{\mathrm{B}}$ with the lattice QCD data [60, 61]. The models are labeled with the value of $g_A^0$ presented in Table 1.

Figure 5

Comparison between the relative contributions of the meson cloud in the holographic model and in the spectator model.