One-quasihomomorphisms from the integers into symmetric matrices

Abstract

A function $f$ from $\mathbb{Z}$ to the symmetric matrices over an arbitrary field $K$ of characteristic $0$ is a $1$-quasihomomorphism if the matrix $f(x+y)-f(x)-f(y)$ has rank at most $1$ for all $x,y\in \mathbb{Z}$. We show that any such $1$-quasihomomorphism has distance at most $2$ from an actual group homomorphism. This gives a positive answer to a special case of a problem posed by Kazhdan and Ziegler.

6 pages, 4 figures, comments welcome