A Hilbert-type theorem for spacelike surfaces with constant Gaussian curvature in $\mathbb{H}^2\times\mathbb{R}_1$

There are examples of complete spacelike surfaces in the Lorentzian product $\mathbb{H}^2\times\mathbb{R}_1$ with constant Gaussian curvature $K\leq -1$. In this paper, we show that there exists no complete spacelike surface in $\mathbb{H}^2\times\mathbb{R}_1$ with constant Gaussian curvature $K>-1$.