Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational arcs as a perturbation of the perfect ring   The image of a point situated at the center of a circularly symmetric
potential is a perfect circle. The perturbative effect of non-symmetrical
potential terms is to displace and break the perfect circle. These 2 effects,
displacement and breaking are directly related to the Taylor expansion of the
perturbation at first order on the circle. The numerical accuracy of this
perturbative approach is tested in the case of an elliptical potential with a
core radius. The contour of the images and the caustics lines are well
re-produced by the perturbative approach. These results suggests that the
modeling of arcs, and in particular of tangential arcs may be simplified by
using a general perturbative representation on the circle. An interesting
feature of the perturbative approach, is that the equation of the caustic line
depends only on the values on the circle of the lens displacement field along
the $\theta$ direction.

27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol