Restriction estimates in a conical singular space: wave equation

Abstract

We study the restriction estimates in a class of conical singular space $X=C(Y)=(0,\infty)_r\times Y$ with the metric $g=\mathrm{d}r^2+r^2h$, where the cross section $Y$ is a compact $(n-1)$-dimensional closed Riemannian manifold $(Y,h)$. Let $\Delta_g$ be the Friedrich extension positive Laplacian on $X$, and consider the operator $\mathcal{L}_V=\Delta_g+V$ with $V=V_0r^{-2}$, where $V_0(\theta)\in\mathcal{C}^\infty(Y)$ is a real function such that the operator $\Delta_h+V_0+(n-2)^2/4$ is positive. In the present paper, we prove a type of modified restriction estimates for the solutions of wave equation associated with $\mathcal{L}_V$. The smallest positive eigenvalue of the operator $\Delta_h+V_0+(n-2)^2/4$ plays an important role in the result. As an application, for independent of interests, we prove local energy estimates and Keel-Smith-Sogge estimates for the wave equation in this setting.