Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Partial mass-degeneracy and spontaneous CP violation in the lepton
  sector   Inspired by the small mass-squared difference measured in the solar neutrino
oscillation experiments and by the testability, we suggest that a limit of the
partial mass degeneracy, in which masses of the first two generation fermions
are degenerate, may be a good starting point for understanding the observed
fermion mass spectra and mixing patterns. The limit indicates the existence of
a two-dimensional rotation symmetry, such as $O(2)$, $D_N$ and so on, in flavor
space of the first two generations. We propose simple models for the lepton
sector based on $D_N$ and show that the models can successfully reproduce the
experimental data without imposing unnatural hierarchies among dimensionless
couplings, although at least $10\%$ tuning is necessary in order to explain a
large atmospheric mixing. It is especially found that the $Z_2$ subgroup of the
$D_N$ symmetry plays an important role in understanding the smallness of the
electron mass and $\theta_{13}^{\rm PMNS}$. We also discuss testability of the
models by the future neutrinoless-double-beta-decay experiments and
cosmological observations.

27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc