Retraction methods and fixed point free maps with null minimal displacements on unit balls

TL;DR

This paper investigates the existence of fixed-point free Lipschitz and Hölder maps on the unit ball of Banach spaces, providing new constructions and answering open questions in the field.

Contribution

It constructs fixed-point free Lipschitz and Hölder maps on Banach space unit balls, especially when the space has a spreading Schauder basis, and extends results to more general settings.

Findings

Existence of fixed-point free Lipschitz maps on spaces with spreading Schauder basis.

Construction of Hölder maps with controlled displacements using recent geometric methods.

Answering an open question about fixed-point free maps with null minimal displacements.

Abstract

In this paper we consider the class of Lipschitz maps on the unit ball $B_X$ of a Banach space $X$, and the question we deal with is whether for any $\lambda>1$ there exists a $\lambda$-Lipschitz fixed-point free mapping $T\colon B_X\to B_X$ with $\mathrm{d}(T,B_X)=0$. We also consider its H\"older version. New related results are obtained. We show that if $X$ has a spreading Schauder basis then such mappings can always be built, answering a question posed by the first author in \cite{Bar}. In the general case, using a recent approach of R. Medina \cite{M} concerning H\"older retractions of $(r_n)$-flat closed convex sets, we show that for any decreasing null sequence $(r_n)\subset \mathbb{R}$ and $\alpha\in (0,1)$, there exists a fixed-point free mapping $T$ on $B_X$ so that $\|T^nx - T^n y\|\leq r_n(\| x - y\|^\alpha +1)$ for all $x, y\in B_X$ and $n\in\mathbb{N}$.