Real polynomials with constrained real divisors. I. Fundamental groups

Gabriel Katz, Boris Shapiro, Volkmar Welker

Published 2019-08-21Version 1

In the late 80s, V.~Arnold and V.~Vassiliev initiated the study of the topology of the space of real univariate polynomials of a given degree d and with no real roots of multiplicity exceeding a given positive integer. Expanding their studies, we consider the spaces of real monic univariate polynomials of degree d whose real divisors avoid sequences of root multiplicities taken from a given poset \Theta of compositions, closed under certain natural combinatorial operations. In this paper, we calculate the fundamental group of these spaces and of some related topological spaces. The mechanism that generates the fundamental groups is similar to the one that produces the braid groups as the fundamental groups of spaces of complex degree d polynomials with no multiple roots. The fundamental groups admit an interpretation as special bordisms of immersions of 1-manifolds into the cylinder S^1 \times \R, immersions whose images avoid the tangency patterns from \Theta with respect to the generators of the cylinder.