J. Barbe, ASYMPTOTICS OF EIGENVALUES FOR HYPOELLIPT IC HAMILTONIANS WITHOUT HOMOGENEITY ASSUMPTION, Comptes rendus de l'Academie des sciences. Serie 1, Mathematique, 326(1), 1998, pp. 31-36
We study here the asymptotic distribution when lambda --> 0(+) of the
eigenvalues less than -lambda of global operators such as p(x, D) - b(
x, D)(-1). We extend classical results for the Schrodinger operator -D
elta - V with potential decaying at infinity.