Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: N-particle sector of quantum field theory as a quantum open system   We give an exposition of a technique, based on the Zwanzig projection
formalism, to construct the evolution equation for the reduced density matrix
corresponding to the n-particle sector of a field theory. We consider the case
of a scalar field with a $g \phi^3$ interaction as an example and construct the
master equation at the lowest non-zero order in perturbation theory.

27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph