  We explore possible signatures for charged lepton flavour violation (LFV),
sparticle discovery at the LHC and dark matter (DM) searches in grand unified
theories (GUTs) based on SU(5), flipped SU(5) (FSU(5)) and SU(4)$_c \times
$SU(2)$_L \times $SU(2)$_R$ (4-2-2). We assume that soft supersymmetry-breaking
terms preserve the group symmetry at some high input scale, and focus on the
non-universal effects on different matter representations generated by gauge
interactions at lower scales, as well as the charged LFV induced in Type-1
see-saw models of neutrino masses. We identify the different mechanisms that
control the relic DM density in the various GUT models, and contrast their LFV
and LHC signatures. The SU(5) and 4-2-2 models offer good detection prospects
both at the LHC and in LFV searches, though with different LSP compositions,
and the SU(5) and FSU(5) models offer LFV within the current reach. The 4-2-2
model allows chargino and gluino coannihilations with neutralinos, and the
former offer good detection prospects for both the LHC and LFV, while gluino
coannihilations lead to lower LFV rates. Our results indicate that LFV is a
powerful tool that complements LHC and DM searches, providing significant
insights into the sparticle spectra and neutrino mass parameters in different
models.
