Many-party correlations between measurement outcomes in general probabilistic
theories are given by conditional probability distributions obeying the
non-signalling condition. We show that any such distribution can be obtained
from classical or quantum theory, by relaxing positivity constraints on either
the mixed state shared by the parties, or the local functions which generate
measurement outcomes. Our results apply to generic non-signalling correlations,
but in particular they yield two distinct quasi-classical models for quantum
correlations.Comment: 6 page
