Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On $dS_4$ extremal surfaces and entanglement entropy in some ghost CFTs   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.

29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat