English

Drazin invertible $(m,P)$-expansive operators

Functional Analysis 2020-12-15 v2

Abstract

A Hilbert space operator TBT\in B is (m,P)(m,P)-expansive, for some positive integer mm and operator PBP\in B, if j=0m(1)j(mj)TjPTj0\sum_{j=0}^m{(-1)^j\left(\begin{array}{clcr}m\\j\end{array}\right)T^{*j}PT^j}\leq 0. No Drazin invertible operator TT can be (m,I)(m,I)-expansive, and if TT is (m,P)(m,P)-expansive for some positive operator PP, then necessarily PP has a decomposition P=P110P=P_{11}\oplus 0. If TT is (m,Tn2)(m,|T^n|^2)-expansive for some positive integer nn, then TnT^n has a decomposition Tn=(U1P1X00)T^n=\left(\begin{array}{clcr}U_1P_1 & X\\0 & 0\end{array}\right); if also (I1XXXX)I\left(\begin{array}{clcr}I_1 & X\\X^* & X^*X\end{array}\right)\geq I, then (P1U1P1X00)\left(\begin{array}{clcr}P_1U_1 & P_1X\\0 & 0\end{array}\right) is (m,I)(m,I)-expansive and (P112U1P112P112X00)\left(\begin{array}{clcr}P^{\frac{1}{2}}_1U_1P^{\frac{1}{2}}_1 & P_1^{\frac{1}{2}}X\\0 & 0\end{array}\right) is (m,I)(m,I)-expansive in an equivalent norm on HH.

Keywords

Cite

@article{arxiv.2010.15480,
  title  = {Drazin invertible $(m,P)$-expansive operators},
  author = {B. P. Duggal and I. H. Kim},
  journal= {arXiv preprint arXiv:2010.15480},
  year   = {2020}
}
R2 v1 2026-06-23T19:44:26.125Z