Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pi excitation of the t-J model   In this paper, we present analytical and numerical calculations of the pi
resonance in the t-J model. We show in detail how the pi resonance in the
particle-particle channel couples to and appears in the dynamical spin
correlation function in a superconducting state. The contribution of the pi
resonance to the spin excitation spectrum can be estimated from general
model-independent sum rules, and it agrees with our detailed calculations. The
results are in overall agreement with the exact diagonalization studies of the
t-J model. Earlier calculations predicted the correct doping dependence of the
neutron resonance peak in the YBCO superconductor, and in this paper detailed
energy and momentum dependence of the spin correlation function is presented.
The microscopic equations of motion obtained within current formalism agree
with that of the SO(5) nonlinear sigma model, where the pi resonance is
interpreted as a pseudo Goldstone mode of the spontaneous SO(5) symmetry
breaking.

17
The categories of this paper are: q-fin
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ
3
The categories of this paper are: physics
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph