Existence of expanding harmonic map flows to hemispheres

Abstract

We show the existence of non-trivial self-expanding harmonic map flows starting from non-energy-minimizing 0-homogeneous maps to a regular ball or a closed hemisphere. In particular, given a non-minimizing but stationary 0-homogeneous harmonic map $u_0$ to a closed hemisphere, we construct infinitely many different weak solutions to harmonic map flow starting from $u_0$, all of which satisfy the parabolic monotonicity formula. We also use a concatenation argument to solve a non-trivial smooth harmonic map flow starting from a given non-minimizing regular 0-homogeneous harmonic map, thereby yielding the non-uniqueness of harmonic map flow with monotonicity formula. This answers a question of Struwe.

arXiv commentThe second version adds the non-uniqueness of harmonic map flow on bounded domains(Corollary 1.2). 18 pages. Comments are welcome!