A stable supermassive charged gravitino?

Abstract: Some time ago it was suggested that dark matter may consist in part of an extremely dilute gas of supermassive gravitinos with fractional charge 2$e$/3 \cite{MeissnerNicolai2019}. This scheme makes the definite (and falsifiable) prediction that massive gravitinos are the {\em only} new fermionic degrees of freedom beyond the known three generations of quarks and leptons of the Standard Model of Particle Physics. In this note we re-examine one special outlier event reported and subsequently discarded by the MACRO collaboration \cite{MACRO1} in the light of this proposal and point out the possibility of an alternative interpretation of this event supporting the above hypothesis, whose confirmation (or refutation) would, however, require an independent dedicated experimental effort.