Spectral properties of non-selfadjoint extensions of the Calogero   Hamiltonian
  We describe all extensions of the Calogero Hamiltonian \[L=-\frac{d^2}{dr^2}+\frac{b}{r^2} \quad \text{in}\ L^2(\mathbb{R}_+), \quad b <-\frac{1}{4}\] having non empty resolvent and generating an analytic semigroup in $L^2(\mathbb{R}_+)$. 
G. Metafune and M. Sobajima
math.AP