Uniform stability of linear evolution equations, with applications to parallel transports

Abstract: I prove the bistability of linear evolution equations $x' = A(t)x$ in a Banach space $E$, where the operator-valued function $A$ is of the form $A(t) = f'(t)G(t,f(t))$ for a binary operator-valued function $G$ and a scalar function $f$. The constant that bounds the solutions of the equation is computed explicitly; it is independent of $f$, in a sense. Two geometric applications of the stability result are presented. Firstly, I show that the parallel transport along a curve $\gamma$ in a manifold, with respect to some linear connection, is bounded in terms of the length of the projection of $\gamma$ to a manifold of one dimension lower. Secondly, I prove an extendability result for parallel sections in vector bundles, thereby answering a question by Antonio J. Di Scala.