Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Derivation of Transport Equations using the Time-Dependent Projection
  Operator Method   We develop a formalism to carry out coarse-grainings in quantum field
theoretical systems by using a time-dependent projection operator in the
Heisenberg picture. A systematic perturbative expansion with respect to the
interaction part of the Hamiltonian is given, and a Langevin-type equation
without a time-convolution integral term is obtained. This method is applied to
a quantum field theoretical model, and coupled transport equations are derived.

33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ