Probing a superlight gravitino in photon-photon collisions.

Abstract

A superlight (of mass \ensuremath{\sim}${M}_{W}^{2}$${M}_{\mathrm{Pl}{}^{\mathrm{\ensuremath{-}}1}}$) gravitino may have observable consequences for high-energy reactions at the teraelectronvolt scale. Tree-level unitarity is shown to break down there for two-photon production of a pair of longitudinally polarized gravitinos. The cross section rises fast with energy and should be measurable at around 100 GeV. A double-tag search for e\ifmmode \bar{e}\else \={e}\fi{}\ensuremath{\rightarrow}e\ifmmode \bar{e}\else \={e}\fi{}+``nothing'' will push up the lower bound on the gravitino mass or detect a superlight gravitino.