Constraints on a possible dineutron state from 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 triton–3He binding energy difference and neutron–deuteron elastic scattering. Due to the appearance of a proton–deuteron 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.