Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: What are the elementary excitations of the BCS model in the canonical
  ensemble?   We have found the elementary excitations of the exactly solvable BCS model
for a fixed number of particles. These turn out to have a peculiar dispersion
relation, some of them with no counterpart in the Bogoliubov picture, and
unusual counting properties related to an old conjecture made by Gaudin. We
give an algorithm to count the number of excitations for each excited state and
a graphical interpretation in terms of paths and Young diagrams. For large
systems the excitations are described by an effective Gaudin model, which
accounts for the finite size corrections to BCS.

27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn