Tetraneutron resonance in the presence of a dineutron

TL;DR

This study investigates the existence of a tetraneutron resonance by solving four-particle equations with various interaction enhancements, finding that previous methods may be misleading and that a true resonance is unlikely under realistic conditions.

Contribution

The paper demonstrates that using uniform interaction enhancement factors leads to virtual states rather than resonances, clarifying previous conflicting results on tetraneutron states.

Findings

A bound tetraneutron can emerge with uniform enhancement but is a virtual state, not a resonance.

Resonant states require selective enhancement of higher partial waves, not uniform enhancement.

Resonance disappears before reaching physical interaction strengths, indicating its unlikely existence.

Abstract

Background: Several previous studies provided contradicting results for the four-neutron system, some claiming the existence of a 0+ near-threshold resonance, others denying presence of any observable resonant states. Purpose: Since most of the studies employed enhanced two-neutron interactions to follow the evolution of an artificially bound state into a continuum one, we examine several enhancement schemes that produce a bound dineutron as well. Methods: We study the four-neutron system by solving exact four-particle equations. By varying the interaction enhancement factor we calculate two-dineutron scattering phase shifts and cross sections. Results: When the same enhancement factor is used in all partial waves, a bound tetraneutron emerges together with a strongly bound dineutron. Furthermore, such a 0+ tetraneutron evolves not into a resonance but into a virtual state. Weak enhancement of S waves together with strongly enhanced higher waves is needed for the emergence of the resonant state. Anyhow the resonant behavior disappears well before reaching the physical interaction strength. Conclusions: The interaction enhancement scheme using the same factor for all waves, employed in several previous works, is misleading for the search of 0+ resonance as only a virtual state can emerge. Evolution of a bound tetraneutron into a resonance via an intermediate virtual state is possible with strong enhancement of higher two-neutron waves.