We discuss asymptotic behavior of the eigenvalue distribution of the
differential form Laplacian on a Riemannian foliated manifold when the metric
on the ambient manifold is blown up in directions normal to the leaves (in the
adiabatic limit). Motivated by analogies with semiclassical spectral
asymptotics, we use ideas and notions of noncommutative geometry to suggest a
conjectural formula for the eigenvalue distribution in the adiabatic limit,
which we call noncommutative Weyl formula. We review known results and discuss
the correctness of the noncommutative Weyl formula in each case.
We prove an asymptotic formula for the number of integer points in a family
of bounded domains in the Euclidean space with smooth boundary, which remain
unchanged along some linear subspace and stretch out in the directions,
orthogonal to this subspace. A more precise estimate for the remainder is
obtained in the case when the domains are strictly convex.
We consider a magnetic Schr\"odinger operator $H^h$, depending on the
semiclassical parameter $h>0$, on a two-dimensional Riemannian manifold. We
assume that there is no electric field. We suppose that the minimal value $b_0$
of the magnetic field $b$ is strictly positive, and there exists a unique
minimum point of $b$, which is non-degenerate. The main result of the paper is
a complete asymptotic expansion for the low-lying eigenvalues of the operator
$H^h$ in the semiclassical limit.
First, we survey some results on classical and quantum dynamical systems
associated with transverse Dirac operators on Riemannian foliations. Then we
illustrate these results by two examples of Riemannian foliations: a foliation
given by the fibers of a fibration and a linear foliation on the
two-dimensional torus.
First, we review the notion of a Poisson structure on a noncommutative
algebra due to Block-Getzler and Xu and introduce a notion of a Hamiltonian
vector field on a noncommutative Poisson algebra. Then we describe a Poisson
structure on a noncommutative algebra associated with a transversely symplectic
foliation and construct a class of Hamiltonian vector fields associated with
this Poisson structure.
This paper gives a survey of the index theory of tangentially elliptic and
transversally elliptic operators on foliated manifolds as well as of related
notions and results in non-commutative geometry.