Localized stem structures in soliton reconnection of the asymmetric Nizhnik-Novikov-Veselov system

The reconnection processes of 3-solitons with 2-resonance can produce distinct local structures that initially connect two pairs of V-shaped branches, then disappear, and later re-emerge as new forms. We call such local structures as stem structures. In this paper, we investigate the variable-length stem structures during the soliton reconnection of the asymmetric Nizhnik-Novikov-Veselov system. We consider two scenarios: weak 2-resonances (i.e., a12 = a13 = 0, 0 < a23 < +∞) and strong 2-resonances (i.e., a12 = a13 = +∞, 0 < a23 < +∞). We determine the asymptotic forms of the four arms and their corresponding stem structures using two-variable asymptotic analysis method which is involved simultaneously with one space variable y (or x) and one temporal variable t. Different from known studies, our findings reveal that the asymptotic forms of the arms S2 and S3 differ by a phase shift as t → ±∞. Building on these asymptotic forms, we perform a detailed analysis of the trajectories, amplitudes, and velocities of the soliton arms and stem structures. Subsequently, we discuss the localization of the stem structures, focusing on their endpoints, lengths, and extreme points in both weak and strong 2-resonance scenarios.