Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Neutrino Mass Hierarchy   The neutrino mass hierarchy, i.e., whether the $\nu_3$ neutrino mass
eigenstate is heavier or lighter than the $\nu_1$ and $\nu_2$ mass eigenstates,
is one of the remaining undetermined fundamental features of the neutrino
Standard Model. Its determination would represent an important step in the
formulation of the generalized model, and would have a profound impact on the
quest of the nature of neutrinos (Dirac or Majorana) and the search for a
theory of flavor. In this review, we summarize the status of experimental and
theoretical work in this field and explore the future opportunities that emerge
in light of the recently discovered non-zero and relatively large third
neutrino mixing angle $\theta_{13}$.

24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
17
The categories of this paper are: q-fin