Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Boson expansion methods applied to a two-level model in the study of
  multiple giant resonances   We apply boson expansion methods to an extended Lipkin-Meshkov-Glick model
including anharmonicities in analogy with previous microscopic calculations. We
study the effects of different approximations present in these calculations,
among which the truncation of the hamiltonian and of the space, in connection
with the study of the properties of two-phonon and three-phonon states. By
comparing the approximate results on the spectrum with the exact ones we
conclude that the approximations made in the microscopic calculations on
two-phonon states are well justified. We find also that a good agreement with
the exact results for the three-phonon state is obtained by using a bosonic
hamiltonian truncated at the fourth order. This result makes us confident that
such approximation can be used in realistic calculations, thus allowing a
theoretical study of triple excitations of giant resonances.

6
The categories of this paper are: astro-ph
29
The categories of this paper are: funct-an
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
28
The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol