Monophoton signals at e+e− colliders in a simplified E6SSM

Abstract

The mono-photon signature emerging in an ${\mathrm{E}}_{6}$ supersymmetric standard model (${\mathrm{E}}_{6}\mathrm{SSM}$) from inert Higgsino dark matter (DM) is analyzed at future ${e}^{+}{e}^{\ensuremath{-}}$ colliders. As the inert neutral and charged Higgsinos are nearly degenerate, the inert chargino is a rather long lived particle and the charged particle associated with its decay to the inert Higgsino is quite soft. We show that the pair production of inert charginos at a 500 GeV electron-positron collider with an initial or final state photon is the most promising channel for probing the inert Higgsino as one DM candidate within the ${\mathrm{E}}_{6}\mathrm{SSM}$. We also emphasize that this signal has no chance of being observed at the Large Hadron Collider (LHC) with higher energy and/or luminosity. Finally, we remark that, combined with a DM signal produced in direct detection (DD) experiments involving an active Higgsino state as the second DM candidate, this dual evidence could point to a two-component DM version of the ${\mathrm{E}}_{6}\mathrm{SSM}$.