Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Violation of Unitarity in Gravitational Subregions   This essay contends that in quantum gravity, some spatial regions do not
admit a unitary Hilbert space. Because the gravitational path integral
spontaneously breaks CPT symmetry, "states" with negative probability can be
identified on either side of trapped surfaces. I argue that these negative norm
states are tolerable, by analogy to quantum mechanics. This viewpoint suggests
a resolution of the firewall paradox, similar to black hole complementarity.
Implications for cosmology are briefly discussed.

37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs
24
The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex