Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A new time-machine model with compact vacuum core   We present a class of curved-spacetime vacuum solutions which develope closed
timelike curves at some particular moment. We then use these vacuum solutions
to construct a time-machine model. The causality violation occurs inside an
empty torus, which constitutes the time-machine core. The matter field
surrounding this empty torus satisfies the weak, dominant, and strong energy
conditions. The model is regular, asymptotically-flat, and
topologically-trivial. Stability remains the main open question.

19
The categories of this paper are: eess
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph