Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: N-quantum approach to quantum field theory at finite T and $\mu$: the
  NJL model   We extend the N-quantum approach to quantum field theory to finite
temperature ($T$) and chemical potential ($\mu$) and apply it to the NJL model.
In this approach the Heisenberg fields are expressed using the Haag expansion
while temperature and chemical potential are introduced simultaneously through
a generalized Bogoliubov transformation. Known mean field results are recovered
using only the first term in the Haag expansion. In addition, we find that at
finite T and in the broken symmetry phase of the model the mean field
approximation can not diagonalize the Hamiltonian. Inclusion of scalar and
axial vector diquark channels in the SU(2)$_{rm f}$ $otimes$ SU(3)$_{\rm c}$
version of the model can lead to a lowering of the vacuum energy density. We
discuss how to go beyond the mean field approximation by including higher order
terms in the Haag expansion.

11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph