Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 3+1 dimensional topological field theory as the effective action of
  neutral fermions   We proposed an action of neutral fermions interacting with external
electromagnetic fields to construct a 3+1 dimensional topological field theory
as the effective action attained by integrating out the fermionic fields in the
related path integral. These neutral quasiparticles are assumed to emerge from
the collective behavior of the original physical particles and holes
(antiparticles). Although our construction is general it is particularly useful
to formulate effective actions of the time reversal invariant topological
insulators.

23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph