Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Axially Symmetric Null dust Spacetime, Naked Singularity and Cosmic Time
  Machine   In this article, we present a gravitational collapse null dust solution of
the Einstein field equations. The spacetime is regular everywhere except on the
symmetry axis where it possesses a naked curvature singularity, and admits one
parameter isometry group, a generator of axial symmetry along the cylinder
which has closed orbits. The space- time admits closed timelike curves (CTCs)
which develop at some particular moment in a causally well-behaved manner and
may represent a Cosmic Time Machine. The radial geodesics near to the
singularity, and the gravitational Lensing (GL) will be discussed. The physical
interpretation of this solution, based on the study of the equation of the
geodesic deviation, will be presented. It was demonstrated that, this solution
depends on the local gravitational field consisting of two components with
amplitude $\Psi_2$, $\Psi_4$.

23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
19
The categories of this paper are: eess
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
2
The categories of this paper are: math