Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Physical and Stable Closed Timelike Curves   We construct a class of closed timelike curves (CTCs) using a compactified
extra dimension $u$. A nonzero metric element $g_{tu}(u)$ enables particles to
travel backwards in global time $t$. The compactified dimension guarantees that
the geodesic curve closes in $u$. The effective 2D ($t$ and $u$) nature of the
metric ensures that spacetime is flat, therein satisfying all the classical
stability conditions as expressed by the energy conditions. Finally,
stationarity of the metric guarantees that a particle's energy is conserved.
The pathologies that plague many hypothesized metrics admitting CTCs, e.g. an
infinite cylinder of matter, a negative energy-distribution, particle
acceleration/blue-shifting along the CTC, do not occur within our metric class.

27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
2
The categories of this paper are: math
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph