Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discussing the U(1)-Problem of QED_2 without Instantons   We construct QED_2 with mass and flavor and an extra Thirring term. The
vacuum expectation values are carefully decomposed into clustering states using
the U(1)-axial symmetry of the considered operators and a limiting procedure.
The properties of the emerging expectation functional are compared to the
proposed theta-vacuum of QCD. The massive theory is bosonized to a generalized
Sine-Gordon model (GSG). The structure of the vacuum of QED_2 manifests itself
in symmetry properties of the GSG. We study the U(1)-problem and derive a
Witten-Veneziano-type formula for the masses of the pseudoscalars determined
from a semiclassical approximation.

29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio