We present recent progress in the understanding of the spectral and subelliptic properties of non-elliptic quadratic operators with application to the study of return to equilibrium for some systems of chains of oscillators. We then explain how these results allow to describe the spectral properties and to give sharp resolvent estimates for some classes of non-selfadjoint pseudodi erential oper...

It is shown that on every finite network with at least one circuit there exist second order differential operators having an infinite number of nonreal eigenvalues. The presence of nonreal eigenvalues implies that these operators cannot be selfadjoint with respect to any metric. These eigenvalues reveal also the existence of oscillatory solutions for the corresponding time–dependent partial dif...

A note is made on the connection between Cliiord analysis and the Weyl functional calculus for an n-tuple of bounded selfadjoint operators which do not necessarily commute with each other.

Motivated by the problem of analytic hypoellipticity, we show that a special family of compact non selfadjoint operators has a non zero eigenvalue. We recover old results obtained by ordinary differential equations techniques and show how it can be applied to the higher dimensional case. This gives in particular a new class of hypoelliptic, but not analytic hypoelliptic operators.

We introduce and study the variational problem to maximize the determinant of a random selfadjoint operators obtained from discrete abelian or nonabelian lattice gauge elds. We prove the existence of minima and give rough estimates of the functional for multi-particle operators.

Distinguished selfadjoint extension of Dirac operators are constructed for a class of potentials including Coulombic ones up to the critical case, −|x|. The method uses Hardy-Dirac inequalities and quadratic form techniques.

A family of selfadjoint operators of the Friedrichs model is considered. These symmetric type operators have one singular point, zero of order m. For every m > 3/2, we construct a rank 1 perturbation from the class Lip1 such that the corresponding operator has a sequence of eigenvalues converging to zero. Thus, near the singular point, there is no singular spectrum finiteness condition in terms...