Abstract
In this paper, we show the Yau’s gradient estimate for harmonic maps into a metric space (X, dX) with curvature bounded above by a constant κ (κ ⩾ 0) in the sense of Alexandrov. As a direct application, it gives some Liouville theorems for such harmonic maps. This extends the works of Cheng (1980) and Choi (1982) to harmonic maps into singular spaces.
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Acknowledgements
The first and third authors were supported by National Natural Science Foundation of China (Grant No. 11521101). The first author was also supported by National Natural Science Foundation of China (Grant No. 11571374) and National Program for Support of Top-Notch Young Professionals. The second author was supported by the Academy of Finland. Part of the work was done when the first author visited the Department of Mathematics and Statistics, University of Jyväskylä for one month in 2016. The first author thanks the department for the hospitality.
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Dedicated to Professor Lo Yang on the Occasion of His 80th Birthday
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Zhang, HC., Zhong, X. & Zhu, XP. Quantitative gradient estimates for harmonic maps into singular spaces. Sci. China Math. 62, 2371–2400 (2019). https://doi.org/10.1007/s11425-018-9493-1
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DOI: https://doi.org/10.1007/s11425-018-9493-1