Is perturbative study of ground-state correlations valid?

TL;DR

This paper examines the validity of perturbative methods for ground-state correlations using a solvable model, revealing cases where they remain accurate even with strong interactions.

Contribution

It demonstrates that perturbative approaches can be valid beyond their traditional perturbative regime through comparison with exact solutions.

Findings

Perturbative methods can be accurate even with strong interactions.

Comparison with exact solutions validates the approach in certain regimes.

The study highlights limitations and conditions for perturbative validity.

Abstract

Perturbative approaches have often been used to include the effects of ground-state correlations in extended theories of the random-phase approximation. Validity of such approaches is investigated for a solvable model where comparison with exact solutions can be made. It is pointed out that there is a case where perturbative approaches give good results in spite of the fact that interaction strength is far beyond a perturbative region.