Light scalar top squark in the minimal supersymmetric grand unified theory

Abstract
We point out that a light scalar top squark with mass as small as mt̃≊20 GeV is still an allowed possibility within the standard, minimal supersymmetry grand unified theory, if the photino exists at mass slightly below the scalar top mass, so that coannihilation efficiently takes place for γ̃γ̃→gg in the early Universe. We show that this case, receiving a number of strong phenomenological constraints, leads to a restricted pattern of the mass spectrum of other supersymmetry particles.