What is the explicit formula for a fundamental solution of the wave operator, where the space variable is in $\mathbb{R}^n$ with $n>1$? Thanks.
The operator I'm talking about is $$L=\partial_{tt}-\Delta_x$$ and for fundamental solution I mean a distribution $E$ (temperate) which satisfies $LE=\delta$ where $\delta$ is the Dirac distribution.
For $n=1$ one of such $E$ is $E(x,t)=(1/2)H(t)H(t^2-x^2)$ where $H$ is the Heaviside function.
I'm looking for expressions in higher dimensions.