Orthogonally invariant random vector
= Orthogonally invariant random vector
A random vector $X\in\mathbb R^d$ is orthogonally invariant when $AX$ has the same distribution as $X$ for every $A\in O(d)$. Its characteristic function is radial and real: $\varphi_X(u)=f(\lVert u\rVert^2)$ for a continuous function $f:[0,\infty)\to\mathbb R$.