Revisiting the Twist-3 Distribution Amplitudes of $K$ Meson within the QCD Background Field Approach

Abstract

In the present paper, we investigate the kaon twist-3 distribution amplitudes (DAs) $ϕ_{p,σ}^K$ within the QCD background field approach. The $SU_f(3)$-breaking effects are studied in detail under a systematical way, especially the sum rules for the moments of $ϕ_{p,σ}^K$ are obtained by keeping all the mass terms in the $s$-quark propagator consistently. After adding all the uncertainties in quadrature, the first two Gegenbauler moments of $ϕ_{p,σ}^K$ are $a^1_{K,p}(1 {\rm GeV}) = -0.376^{+0.103}_{-0.148}$, $a^2_{K,p}(1 {\rm GeV}) = 0.701^{+0.481}_{-0.491}$, $a^1_{K,σ}(1 {\rm GeV}) = -0.160^{+0.051}_{-0.074}$ and $a^2_{K,σ}(1 {\rm GeV}) = 0.369^{+0.163}_{-0.149}$, respectively. Their normalization parameters $μ_K^p |_{1\rm GeV} = 1.188^{+0.039}_{-0.043}$ GeV and $μ_K^σ|_{1\rm GeV} = 1.021^{+0.036}_{-0.055}$ GeV. A detailed discussion on the properties of $ϕ^K_{p,σ}$ moments shows that the higher-order $s$-quark mass terms can indeed provide sizable contributions. Furthermore, based on the newly obtained moments, a model for the kaon twist-3 wavefunction $Ψ_{p,σ}^K(x,\mathbf{k}_\perp)$ with a better end-point behavior is constructed, which shall be useful for perturbative QCD calculations. As a byproduct, we make a discussion on the properties of the pion twist-3 DAs.