Constraints on a possible dineutron state from pionless EFT

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– 3 He binding energy difference and neutron–deuteron elastic scattering. Due to the appearance of a proton–deuteron three-body counterterm at this order, the triton– 3 He 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