Constraints on a possible dineutron state from pionless EFT

TL;DR

This paper uses pionless effective field theory to analyze the neutron-neutron scattering length's impact on three-nucleon systems, concluding that a bound dineutron cannot be ruled out at next-to-leading order.

Contribution

It provides a next-to-leading order analysis showing the insensitivity of certain observables to large neutron-neutron scattering lengths, allowing a bound dineutron to remain plausible.

Findings

The triton-3He binding energy difference is consistent with experimental data.

Neutron-deuteron elastic scattering phase shifts are insensitive to neutron-neutron scattering length variations.

A bound dineutron cannot be excluded at next-to-leading order in pionless EFT.

Abstract

We investigate the sensitivity of the three-nucleon system to changes in the neutron-neutron scattering length to next-to-leading order in the pionless effective field theory, focusing on the the triton-3He binding energy difference and neutron-deuteron elastic scattering. Due to the appearance of an electromagnetic three-body counterterm at this order, the triton-3He binding energy difference remains consistent with the experimental value even for large positive neutron-neutron scattering lengths while the elastic neutron-deuteron scattering phase shifts are insensitive. We conclude that a bound dineutron cannot be excluded to next-to-leading order in pionless EFT.