  In arXiv:1501.03019 [hep-th], the areas of certain complex extremal surfaces
in de Sitter space were found to have resemblance with entanglement entropy in
appropriate dual Euclidean non-unitary CFTs, with the area being real and
negative in $dS_4$. In this paper, we study some toy models of 2-dim ghost
conformal field theories with negative central charge with a view to exploring
this further from the CFT point of view. In particular we consider $bc$-ghost
systems with central charge $c=-2$ and study the replica formulation for
entanglement entropy for a single interval, and associated issues arising in
this case, notably pertaining to (i) the $SL(2)$ vacuum coinciding with the
ghost ground state, and (ii) the background charge inherent in these systems
which leads to particular forms for the norms of states (involving zero modes).
This eventually gives rise to negative entanglement entropy. We also discuss a
(logarithmic) CFT of anti-commuting scalars, with similarities in some
features. Finally we discuss a simple toy model of two "ghost-spins" which
mimics some of these features.
