a1(1260)-meson longitudinal twist-2 distribution amplitude and the D→a1(1260)ℓ+νℓ decay processes.

In the paper, we investigate the moments ⟨ ξ 2 ; a 1 ‖ ; n ⟩ of the axial-vector a 1 (1260) -meson distribution amplitude by using the QCD sum rules approach under the background field theory. By considering the vacuum condensates up to dimension-six and the perturbative part up to next-to-leading order QCD corrections, its first five moments at an initial scale μ 0 = 1 GeV are ⟨ ξ 2 ; a 1 ‖ ; 2 ⟩ | μ 0 = 0.223 ± 0.029 , ⟨ ξ 2 ; a 1 ‖ ; 4 ⟩ | μ 0 = 0.098 ± 0.008 , ⟨ ξ 2 ; a 1 ‖ ; 6 ⟩ | μ 0 = 0.056 ± 0.006 , ⟨ ξ 2 ; a 1 ‖ ; 8 ⟩ | μ 0 = 0.039 ± 0.004 and ⟨ ξ 2 ; a 1 ‖ ; 10 ⟩ | μ 0 = 0.028 ± 0.003 , respectively. We then construct a light-cone harmonic oscillator model for a 1 (1260) -meson longitudinal twist-2 distribution amplitude ϕ 2 ; a 1 ‖ (x , μ) , whose model parameters are fitted by using the least squares method. As an application of ϕ 2 ; a 1 ‖ (x , μ) , we calculate the transition form factors (TFFs) of D → a 1 (1260) in large and intermediate momentum transfers by using the QCD light-cone sum rules approach. At the largest recoil point ( q 2 = 0 ), we obtain A (0) = 0. 130 - 0.013 + 0.015 , V 1 (0) = 1. 898 - 0.121 + 0.128 , V 2 (0) = 0. 228 - 0.021 + 0.020 , and V 0 (0) = 0. 217 - 0.025 + 0.023 . By applying the extrapolated TFFs to the semi-leptonic decay D 0 (+) → a 1 - (0) (1260) ℓ + ν ℓ , we obtain B (D 0 → a 1 - (1260) e + ν e) = (5. 261 - 0.639 + 0.745) × 10 - 5 , B (D + → a 1 0 (1260) e + ν e) = (6. 673 - 0.811 + 0.947) × 10 - 5 , B (D 0 → a 1 - (1260) μ + ν μ) = (4. 732 - 0.590 + 0.685) × 10 - 5 , B (D + → a 1 0 (1260) μ + ν μ) = (6. 002 - 0.748 + 0.796) × 10 - 5 . [ABSTRACT FROM AUTHOR]