Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Weak interactions in a background of a uniform magnetic field. A
  mathematical model for the inverse beta decay.I   In this paper we consider a mathematical model for the inverse beta decay in
a uniform magnetic field. With this model we associate a Hamiltonian with
cutoffs in an appropriate Fock space. No infrared regularization is assumed.
The Hamiltonian is selfadjoint and has a ground state. We study its essential
spectrum and determine its spectrum. Conditions for uniqueness of ground state
are given. The coupling constant is supposed suffciently small.

10
The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
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The categories of this paper are: eess
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys