Physics Letters B 779 (2018) 430–435
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
New class of two-loop neutrino mass models with distinguishable
phenomenology
Qing-Hong Cao
a,b,c,∗
, Shao-Long Chen
d,c,∗
, Ernest Ma
e
, Bin Yan
a
, Dong-Ming Zhang
a,∗
a
Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China
b
Collaborative Innovation Center of Quantum Matter, Beijing, 100871, China
c
Center for High Energy Physics, Peking University, Beijing 100871, China
d
Key Laboratory of Quark and Lepton Physics (MoE) and Institute of Particle Physics, Central China Normal University, Wuhan 430079, China
e
Physics & Astronomy Department and Graduate Division, University of California, Riverside, CA 92521, USA
a r t i c l e i n f o a b s t r a c t
Article history:
Received
13 October 2017
Received
in revised form 26 January 2018
Accepted
16 February 2018
Available
online 21 February 2018
Editor:
M. Cveti
ˇ
c
We discuss a new class of neutrino mass models generated in two loops, and explore specifically three
new physics scenarios: (A) doubly charged scalar, (B) dark matter, and (C) leptoquark and diquark, which
are verifiable at the 14 TeV LHC Run-II. We point out how the different Higgs insertions will distinguish
our two-loop topology with others if the new particles in the loop are in the simplest representations of
the SM gauge group.
© 2018 Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
The minimal particle content of the standard model (SM) of
quarks and leptons does not allow a nonzero neutrino mass at the
level of a renormalizable Lagrangian. However, it has long been
known [1] that an effective dimension-five operator exists for ob-
taining
a nonzero Majorana neutrino mass, i.e.
L
5
=−
κ
ij
(
ν
i
φ
0
−l
i
φ
+
)(ν
j
φ
0
−l
j
φ
+
) + H.c., (1)
where (ν
i
, l
i
), i = 1, 2, 3are the three left-handed lepton dou-
blets
of the SM and (φ
+
, φ
0
) is the one Higgs scalar doublet. As
φ
0
acquires a nonzero vacuum expectation value φ
0
= v/
√
2 =
174 GeV, the neutrino mass matrix is given by
M
ν
ij
=
κ
ij
v
2
.
(2)
Tree-level [2–6] and one-loop realizations [7–12]of this operator
have been discussed extensively in the literature, as well as some
two-loop [12–22] and three-loop [23–25]examples. The two-loop
*
Corresponding authors.
E-mail
addresses: qinghongcao @pku .edu .cn (Q.-H. Cao), chensl @mail .ccnu .edu .cn
(S.-L. Chen),
ma @phyun8 .ucr.edu (E. Ma), binyan @pku .edu .cn (B. Yan),
zhangdongming @pku .edu .cn (D.-M. Zhang).
Fig. 1. Two-loop skeleton diagrams for neutrino mass before the Higgs insertions.
case is particularly inviting because the smallness of the neu-
trino
mass, i.e. of order 0.1 eV, agrees well with a mass scale
of O(1) TeV for the heavy particles in the loops, without unduly
small and large Yukawa and scalar couplings, as would be the case
with one-loop and three-loop realizations.
Generic
structures of the two-loop diagrams involving fermions
and scalars are shown in Fig. 1, where the external Higgs lines are
yet to be inserted [21]. To minimize the particle content inside the
loops, we assume that the topology of each diagram exhibits a left-
right
or central symmetry. Under such a condition, Figs. 1(a)–(d)
may very well have a singlet Majorana fermion that could it-
self
generate a neutrino mass at tree level. The only exception is
https://doi.org/10.1016/j.physletb.2018.02.038
0370-2693/
© 2018 Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.