Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coupling between superfluid neutrons and superfluid protons in the
  elementary excitations of neutron star matter   Several phenomena occurring in neutron stars are affected by the elementary
excitations that characterize the stellar matter. In particular, low-energy
excitations can play a major role in the emission and propagation of neutrinos,
neutron star cooling and transport processes. In this paper, we consider the
elementary modes in the star region where both proton and neutron components
are superfluid.
  We study the overall spectral functions of protons, neutrons and electrons on
the basis of the Coulomb and nuclear interactions.
  This study is performed in the framework of the Random Phase Approximation,
generalized to superfluid systems. The formalism we use ensures that the
Generalized Ward's Identities are satisfied. We focus on the coupling between
neutrons and protons. On one hand this coupling results in collective modes
that involve simultaneously neutrons and protons, on the other hand it produces
a damping of the excitations. Both effects are especially visible in the
spectral functions of the different components of the matter. At high density
while the neutrons and protons tend to develop independent excitations, as
indicated by the spectral functions, the neutron-proton coupling still produces
a strong damping of the modes.

8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th