Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Neutron-proton mass difference in nuclear matter   Isospin-breaking effects in nuclear matter are studied in the framework of a
medium-modified Skyrme model. The proposed effective Lagrangian incorporates
both the medium influence of the surrounding nuclear environment on the single
nucleon properties and an explicit isospin-breaking effect in the mesonic
sector. The approach predicts that the neutron-proton mass difference decreases
in isospin-symmetric nuclear matter but by a very small amount only.

8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc