The existence of stable clusters of four neutrons called tetraneutrons has been hypothesised by a team led by Francisco-Miguel Marqués at the CNRS Laboratory for Nuclear Physics based on observations of the disintegration of beryllium-14 nuclei.
This is a potentially significant discovery because current theory suggests that these clusters should not be stable, and thus should not exist. Therefore, if the existence of stable tetraneutrons can be independently confirmed, adjustments will have to be made to current physical theories.
