On the resolvent of $H+A^{*}+A$

TL;DR

This paper provides a concise proof and explicit formulas for the resolvent and self-adjoint domains of Hamiltonians of the form H+A*+A, relevant in quantum field theory, and characterizes their limits via cutoff Hamiltonians with renormalization.

Contribution

It offers a simplified proof and explicit resolvent representations for self-adjoint realizations of H+A*+A Hamiltonians, extending previous results with a clear limit characterization.

Findings

Explicit resolvent formulas derived

Self-adjoint domains explicitly characterized

Limit of cutoff Hamiltonians with renormalization established

Abstract

We present a much shorter and streamlined proof of an improved version of the results previously given in [A. Posilicano: On the Self-Adjointness of $H+A^{*}+A$, Math. Phys. Anal. Geom. (2020)] concerning the self-adjoint realizations of formal QFT-like Hamiltonians of the kind $H+A^{*}+A$, where $H$ and $A$ play the role of the free field Hamiltonian and of the annihilation operator respectively. We give explicit representations of the resolvent and of the self-adjointness domain; the consequent Krein-type resolvent formula leads to a characterization of these self-adjoint realizations as limit (with respect to convergence in norm resolvent sense) of cutoff Hamiltonians of the kind $H+A^{*}_{n}+A_{n}-E_{n}$, the bounded operator $E_{n}$ playing the role of a renormalizing counter term.