Injectivity of non-singular planar maps with disconnecting curves in the eigenvalues space

Abstract

Fessler and Gutierrez \cite{Fe,Gu} proved that if a non-singular planar map has Jacobian matrix without eigenvalues in $(0,+\infty )$, then it is injective. We prove that the same holds replacing $(0,+\infty )$ with any unbounded curve disconnecting the upper (lower) complex half-plane. Additionally we prove that a Jacobian map $(P,Q)$ is injective if $P_x+Q_y$ is not a surjective function.