Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two-proton radioactivity   In the first part of the present review paper, experimental results which
lead to the discovery of two-proton radioactivity are reviewed. Beyond
two-proton emission from nuclear ground states, we also discuss experimental
studies of two-proton emission from excited states populated either by nuclear
beta decay or by inelastic reactions. In the second part, we review the modern
theory of two-proton radioactivity. An outlook to future experimental studies
and theoretical developments will conclude this review.

16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph