  A low-background inclusive search for new physics in events with same-sign
dileptons is presented. The search uses proton-proton collisions corresponding
to 20.3 fb$^{-1}$ of integrated luminosity taken in 2012 at a centre-of-mass
energy of 8 TeV with the ATLAS detector at the LHC. Pairs of isolated leptons
with the same electric charge and large transverse momenta of the type
$e^{\pm}e^{\pm}, e^{\pm}\mu^{\pm}$, and $\mu^{\pm}\mu^{\pm}$ are selected and
their invariant mass distribution is examined. No excess of events above the
expected level of Standard Model background is found. The results are used to
set upper limits on the cross-sections for processes beyond the Standard Model.
Limits are placed as a function of the dilepton invariant mass within a
fiducial region corresponding to the signal event selection criteria. Exclusion
limits are also derived for a specific model of doubly charged Higgs boson
production.
