@article{Li2023, 
author = {Yanyan Li and Han Lu and Siyuan Lu},
title = {A Liouville Theorem for Möbius Invariant Equations},
year = {2023},
journal = {Peking Mathematical Journal},
volume = {6},
number = {2},
pages = {609-634},
keywords = {Liouville theorem, Möbius invariant, Fully nonlinear elliptic equations},
url = {https://www.sciopen.com/article/10.1007/s42543-021-00043-9},
doi = {10.1007/s42543-021-00043-9},
abstract = {In this paper, we classify Möbius invariant differential operators of second order in two-dimensional Euclidean space, and establish a Liouville type theorem for general Möbius invariant elliptic equations. The equations are naturally associated with a continuous family of convex cones  Γp in  R2, with parameter  p∈[1,2], joining the half plane  Γ1:={(λ1,λ2):λ1+λ2>0} and the first quadrant  Γ2:={(λ1,λ2):λ1,λ2>0}. Chen and C. M. Li established in 1991 a Liouville type theorem corresponding to  Γ1 under an integrability assumption on the solution. The uniqueness result does not hold without this assumption. The Liouville type theorem we establish in this paper for  Γp,  1<p≤2, does not require any additional assumption on the solution as for  Γ1. This is reminiscent of the Liouville type theorems in dimensions  n≥3 established by Caffarelli, Gidas and Spruck in 1989 and by A. B. Li and Y. Y. Li in 2003–2005, where no additional assumption was needed either. On the other hand, there is a striking new phenomena in dimension  n=2 that  Γp for  p=1 is a sharp dividing line for such uniqueness result to hold without any further assumption on the solution. In dimensions  n≥3, there is no such dividing line.}
}