Hessian matrix

$\displaystyle H=\left(\begin{array}{cc}\alpha(\alpha-1)x^{\alpha-2}y^{\beta}&\alpha\beta x^{\alpha-1}y^{\beta-1}\\\alpha\beta x^{\alpha-1}\beta^{\beta-1}&\beta(\beta-1)x^{\alpha}y^{\beta-2}\end{array}\right) $

if $\displaystyle det(H)<0 $

what can we say about it?