Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Proper weak-coupling approach to the periodic s-d(f) exchange model   The periodic s-d(f) exchange model is characterized by a wide variety of
interesting applications, a simple mathematical structure and a limited number
of reliable approximations which take care of the quantum nature of the
participating spins. We suggest the use of a projection-operator method for
getting information perturbationally, which are not accessible via diagrammatic
approaches. In this paper we present in particular results beyond perturbation
theory, which are obtained such that almost all exactly known limiting cases
are incorporated correctly. We discuss a variety of possible methods and
evaluate their consequences for one-particle properties. These considerations
serve as a guideline for a more effective approach to the model.

30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom