The Borsuk-Ulam property for homotopy classes on bundles, parametrized braids groups and applications for surfaces bundles

Abstract

Let $M$ and $N$ be fiber bundles over the same base $B$, where $M$ is endowed with a free involution $\tau$ over $B$. A homotopy class $\delta \in [M,N{]}_B$ (over $B$) is said to have the Borsuk-Ulam property with respect to $\tau$ if for every fiber-preserving map $f:M\to N$ over $B$ which represents $\delta$ there exists a point $x\in M$ such that $f(\tau (x))=f(x)$. In the cases that $B$ is a $K(\pi ,1)$-space and the fibers of the projections $M\to B$ and $N\to B$ are $K(\pi ,1)$ closed surfaces $S_M$ and $S_N$, respectively, we show that the problem of decide if a homotopy class of a fiber-preserving map $f:M\to N$ over $B$ has the Borsuk-Ulam property is equivalent of an algebraic problem involving the fundamental groups of $M$, the orbit space of $M$ by $\tau$ and a type of generalized braid groups of $N$ that we call parametrized braid groups. As an application, we determine the homotopy classes of self fiber-preserving maps of some 2-torus bundles over ${\mathbb{S}}^1$ that satisfy the Borsuk-Ulam property with respect to certain involutions $\tau$ over ${\mathbb{S}}^1$.