  A search for single top-quark production via flavour-changing neutral current
processes from gluon plus up- or charm-quark initial states in proton-proton
collisions at the LHC is presented. Data collected with the ATLAS detector in
2012 at a centre-of-mass energy of 8 TeV and corresponding to an integrated
luminosity of 20.3 fb$^{-1}$ are used. Candidate events for a top quark
decaying into a lepton, a neutrino and a jet are selected and classified into
signal- and background-like candidates using a neural network. No signal is
observed and an upper limit on the production cross-section multiplied by the
$t \rightarrow \ell\nu b$ branching fraction is set. The observed 95% CL limit
is $\sigma_{qg \rightarrow t} \times \mathcal{B}(t \rightarrow Wb) \times
\mathcal{B}(W \rightarrow \ell \nu) < 3.4$ pb and the expected 95% CL limit is
$\sigma_{qg \rightarrow t} \times \mathcal{B}(t \rightarrow Wb) \times
\mathcal{B}(W \rightarrow \ell \nu) < 2.9$ pb. The observed limit can be
interpreted as upper limits on the coupling constants of the flavour-changing
neutral current interactions divided by the scale of new physics
$\kappa_{ugt}/\Lambda < 10 \times 10^{-3}$ TeV$^{-1}$ and $\kappa_{cgt}/\Lambda
< 23 \times 10^{-3}$ TeV$^{-1}$ and on the branching fractions $\mathcal{B}(t
\rightarrow ug) < 1.2 \times 10^{-4}$ and $\mathcal{B}(t \rightarrow cg) < 6.4
\times 10^{-4}$.
