Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Spectrum of a Model Operator in Fock Space   A model operator $H$ associated to a system describing four particles in
interaction, without conservation of the number of particles, is considered. We
describe the essential spectrum of $H$ by the spectrum of the channel operators
and prove the Hunziker-van Winter-Zhislin (HWZ) theorem for the operator $H.$
We also give some variational principles for boundaries of the essential
spectrum and interior eigenvalues.

6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex