Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Geometrical particle models on 3D null curves   The simplest (2+1)-dimensional mechanical systems associated with light-like
curves, already studied by Nersessian and Ramos, are reconsidered. The action
is linear in the curvature of the particle path and the moduli spaces of
solutions are completely exhibited in 3-dimensional Minkowski background, even
when the action is not proportional to the pseudo-arc length of the trajectory.

20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
23
The categories of this paper are: solv-int