From a Gap in the Lyapunov Spectrum to Dominated Splittings

Let $A$ be an $\alpha$-Hölder cocycle over a transitive two-sided subshift of finite type, and assume that $A$ is strongly bunched. We prove that if there exist $k\in \{1,\dots ,d-1\}$ and $c>0$ such that $${\lambda }_k(p)-{\lambda }_{k+1}(p)\ge c$$ for every periodic point $p$, then $A$ admits a dominated splitting of index $k$. Thus, under strong bunching, a uniform asymptotic gap in the Lyapunov spectrum of periodic measures implies a uniform geometric splitting along all orbit segments. This extends the periodic-gap criterion of Kassel–Potrie from locally constant cocycles to Hölder cocycles in arbitrary dimension, and extends the two-dimensional fiber-bunched result of Velozo to higher dimensions under the stronger bunching assumption.