Conjugate Real Classes in General Linear Groups

Abstract

Let $\F$ be a field with a non-trivial involution $c:\alpha \to {\alpha }^c$. An element $g \in {\rm GL}_n(\F)$ is called $c$-real if it is conjugate to $(g^c{)}^{-1}$. We prove that for $n\ge 2$, $g \in {\rm GL}_n(\F)$ is $c$-real if and only if it has a representation in some unitary group of degree $n$ over $\F$.

minor revision. Fixed minor errors