Spectra and semigroup smoothing for non-elliptic quadratic operators
Spectra and semigroup smoothing for non-elliptic quadratic operators
We study non-elliptic quadratic differential operators. Quadratic differential operators are non-selfadjoint operators defined in the Weyl quantization by complex-valued quadratic symbols. When the real part of their Weyl symbols is a non-positive quadratic form, we point out the existence of a particular linear subspace in the phase space intrinsically associated …