Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Schwinger Model and the Physical Projector: a Nonperturbative
  Quantization without Gauge Fixing   Based on the physical projector approach, a nonpertubative quantization of
the massless Schwinger model is considered which does not require any gauge
fixing. The spectrum of physical states, readily identified following a
diagonalization of the operator algebra, is that of a massive pseudoscalar
field, namely the electric field having acquired a mass proportional to the
gauge coupling constant. The physical spectrum need not be identified with
confined bound fermion-antifermion pairs, an interpretation which one is
otherwise led to given whatever gauge fixing procedure but which is not void of
gauge fixing artefacts.

28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex