Non-constancy and multiplicity of half-harmonic maps from intervals into the circle

Ali Hyder; Luca Martinazzi

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arXiv · 2607.20016

Non-constancy and multiplicity of half-harmonic maps from intervals into the circle

Ali Hyder·Luca Martinazzi

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Abstract

We study one-dimensional half-harmonic maps from the real line into the circle with prescribed exterior data. We show that, for every positive integer $k$, if two disjoint intervals are sufficiently close, there exist at least $k$ distinct non-constant half-harmonic maps with constant exterior data. More generally, we establish a multiplicity result for boundary data with energy below the critical threshold $2\pi$ by introducing a local relative degree and proving corresponding degree-jump estimates. Working on a single interval and for boundary data arising as traces of finite Blaschke products, we investigate the existence and non-existence of energy minimizers in prescribed degree classes.

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Ali Hyder, Luca Martinazzi. 2026-07-22. Non-constancy and multiplicity of half-harmonic maps from intervals into the circle. https://arxiv.org/abs/2607.20016

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