On the Third Gap for Proper Holomorphic Maps between Balls

In this paper, we study the gap rigidity phenomenon for proper holomorphic maps between balls of different dimension. We show that any $F\in prop_3({\mathbb{B}}^n, {\mathbb{B}} ^N)$, with $3n<N\leq 4n-7$ and $n\geq 7$, is equivalent to a map of the form $(G,0)$ with $G\in Rat ({\mathbb{B}}^n,{\mathbb{B}}^{3n})$. The main ingredients for the proof of our main theorem are the normal form obtained by Huang-Ji-Xu and a lemma of the first author.