On slant helices in Minkowski space $E_1^3$

We consider a curve $\alpha=\alpha(s)$ in Minkowski 3-space $E_1^3$ and denote by \{T,N,B} the Frenet frame of $\alpha$. We say that $\alpha$ is a slant helix if there exists a fixed direction $U$ of $E_1^3$ such that the function $<N(s),U>$ is constant. In this work we give characterizations of slant helices in terms of the curvature and torsion of $\alpha$.