Asymptotic analysis and qualitative behavior at the free boundary for Sacks-Uhlenbeck α-harmonic maps
Jürgen Jost, Lei Liu, and Miaomiao Zhu
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Submission date: 24. Oct. 2017 (revised version: June 2019)
Keywords and phrases: harmonic map, $\alpha$-harmonic map, free boundary, blow-up, energy identity, neck analysis
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We investigate the possible blow-up behavior of sequences of Sacks-Uhlenbeck α-harmonic maps from a compact Riemann surface with boundary to a compact Riemannian manifold N with a free boundary on a closed submanifold K ⊂ N. We discover and explore a new phenomenon, that the connection between bubbles, instead of being a geodesic joining them, can be a more general curve that involves the geometry of both N and K. In technical terms, by comparing the blow-up radius with the distance between the blow-up position and the boundary, we deﬁne a new quantity, based on which we show a generalized energy identity for the blow-up sequence and give new length formulas for the necks in the case that there is only one bubble occurring at a boundary blow-up point.