  We compute the hadronic matrix elements of the four-quark operators needed
for the study of neutral kaon mixing beyond the Standard Model (SM). We use
nf=2+1 flavours of domain-wall fermions (DWF) which exhibit good chiral-flavour
symmetry. The renormalization is performed non-perturbatively through the
RI-MOM scheme and our results are converted perturbatively to MSbar. The
computation is performed on a single lattice spacing a=0.086 fm with a lightest
unitary pion mass of 290 MeV. The various systematic errors, including the
discretisation effects, are estimated and discussed. Our results confirm a
previous quenched study, where large ratios of non-SM to SM matrix elements
were obtained.
