I want to apply a theorem that describes the eigenfunctions of the Laplacian on a Riemannian manifold:
- This theorem assumes that the geodesic flow of $M$ is ergodic with respect to the Liouville measure.
- What is exactly the definition of the Liouville measure ?: Is it defined on $M$ or $TM$ ?.
- In another reference, I saw that this measure is expressed as
$$
\frac{{\rm d}x \wedge {\rm d}\xi}{{\rm d}\left\vert\,\xi\,\right\vert}
$$
- Could someone please explain this definition ?.
I could not find it in any textbook.
- Could someone please explain this definition ?.