An estimate for the number of eigenvalues of a Hilbert--Schmidt operator in a half-plane

Abstract

Let $A$ and $\tilde{A}$ be Hilbert--Schmidt operators. For a constant $r>0$, let $i_+(r, A)$ be the number of the eigenvalues of $A$ taken with their multiplicities lying in the half-plane $\{z\in\mathbb{C}: \Re z>r\}$. We suggest the conditions that provide the equality $i_+(r, \tilde{A})=i_+(r, A)$.