Next-to-Next-to-Leading-Order QCD Corrections to Pion Electromagnetic Form Factors.

We calculate the next-to-next-to-leading-order (NNLO) QCD radiative correction to the pion electromagnetic form factor with large momentum transfer. We explicitly verify the validity of the collinear factorization to two-loop order for this observable and obtain the respective IR-finite two-loop hard-scattering kernel in the closed form. The NNLO QCD correction turns out to be positive and significant. Incorporating this new ingredient of correction, we then make a comprehensive comparison between the finest theoretical predictions and numerous data for both space- and timelike pion form factors. Our phenomenological analysis provides a strong constraint on the second Gegenbauer moment of the pion light-cone distribution amplitude obtained from recent lattice QCD studies.

Next-to-Next-to-Leading Order Calculation of Quasiparton Distribution Functions.

We present the next-to-next-to-leading order (NNLO) calculation of quark quasiparton distribution functions (PDFs) in the large momentum effective theory. The nontrivial factorization at this order is established explicitly and the full analytic matching coefficients between the quasidistribution and the light-cone distribution are derived. We demonstrate that the NNLO numerical contributions can improve the behavior of the extracted PDFs sizably. With the unprecedented precision study of nucleon tomography at the planned electron-ion collider, high precision lattice QCD simulations with our NNLO results implemented will enable to test the QCD theory and more precise results on the PDFs of nucleons will be obtained.

Effects of forest gap disturbance on forest ecosystem.

Forest gap disturbance has important consequences on plant species assemblage, stand structure and ecosystem functions of forests via changing micro-scale heterogeneity and community succession. Here, we reviwed research progress in the effects of forest gap disturbance on forest ecosystem. The effects of forest gap disturbance on plant species assemblage was analyzed based on the intrinsic biological characteristics and external environmental factors. The effects of forest gap disturbance on stand structure was discussed from the perspectives of texture and architecture of plant community. Forest gap disturbance effect on forest ecosystem functions was reviewed. After analyzing the theoretical shortcomings and the key bottleneck of forest ecosystem management practices, the following research directions were proposed, including the methods of determining threshold of forest gap, the mechanism of canopy closure, the effect of forest gap disturbance on forest ecosystem processes, and the relationship between forest gap disturbance and forest productivity. The advantage of forest gap disturbance in accelerating plant species regeneration and structure complexities could provide scientific evidence for enhancing the quality of low yield and low function plantations in China.