N.H. Thao et al. / Nuclear Physics B 921 (2017) 159–180 163
Table 1
Couplings
relating with LFVHD in seesaw models. Here, C
ij
=
3
c=1
U
ν
ci
U
ν∗
cj
. The p
0
, p
+
and p
−
are incoming
momenta of h, G
+
W
and G
−
W
, respectively.
Vertex Coupling Vertex Coupling
hW
+μ
W
−ν
igm
W
g
μν
hG
+
W
G
−
W
−
igm
2
h
2m
W
hG
+
W
W
−μ
ig
2
(
p
+
−p
0
)
μ
hG
−
W
W
+μ
ig
2
(
p
0
−p
−
)
μ
n
i
e
a
W
+
μ
ig
√
2
U
ν
ai
γ
μ
P
L
e
a
n
i
W
−
μ
ig
√
2
U
ν∗
ai
γ
μ
P
L
n
i
e
a
G
+
W
−
ig
√
2m
W
U
ν
ai
m
e
a
P
R
−m
n
i
P
L
e
a
n
i
G
−
W
−
ig
√
2m
W
U
ν∗
ai
m
e
a
P
L
−m
n
i
P
R
h
n
i
n
j
−ig
2m
W
C
ij
P
L
m
n
i
+P
R
m
n
j
+ C
∗
ij
P
L
m
n
j
+P
R
m
n
i
h
e
a
e
a
−
igm
e
a
2m
W
M
ν
ab
=0,M
ν
(I +3)(J +3)
=(m
N
)
IJ
,M
ν
a(I+3)
=(M
D
)
aI
,M
ν
(I +3)a
=(M
T
D
)
Ia
,
U
ν†
U
ν
=I, M
ν
=U
ν∗
ˆ
M
ν
U
ν†
, and M
ν∗
=U
ν
ˆ
M
ν
U
νT
. (9)
The first term in the left hand side of Eq. (8) will change exactly into the second term in the right
hand side of Eq. (8), after mediate steps of transformation, namely
M
ν
a(I+3)
U
ν
ai
U
ν
(I +3)j
=
U
ν∗
ˆ
M
ν
U
ν†
a(I+3)
U
ν
ai
U
ν
(I +3)j
=U
ν∗
ak
m
n
k
U
ν†
k(I+3)
U
ν
ai
U
ν
(I +3)j
=U
ν∗
ak
U
ν
ai
m
n
k
K+3
l=1
U
ν†
kl
U
ν
lj
−
3
b=1
U
ν†
kb
U
ν
bj
=U
ν∗
ak
U
ν
ai
m
ν
k
δ
kj
−U
ν†
kb
U
ν
bj
=U
ν∗
aj
U
ν
ai
m
n
j
−U
ν
ai
U
ν
bj
U
ν∗
ak
m
n
k
U
ν†
kb
=U
ν∗
aj
U
ν
ai
m
n
j
−U
ν
ai
U
ν
bj
M
ν∗
ab
=U
ν
ai
U
ν∗
aj
m
n
j
. (10)
From (10), the second term in the left hand side of (8) can be derived easily, M
ν∗
a(I+3)
U
ν∗
(I +3)i
×
U
ν∗
aj
=
M
ν
a(I+3)
U
ν
aj
U
ν
(I +3)i
∗
=
U
ν
aj
U
ν∗
ai
m
n
i
∗
= U
ν
ai
U
ν∗
aj
m
n
i
. Finally, the Feynman rule for
the vertex (8) with two Majorana leptons h
n
i
n
j
must be expressed in a symmetric form,
2
namely −
g
4m
W
i,j
n
i
m
n
i
C
ij
+m
n
j
C
∗
ij
P
L
+
m
n
j
C
ij
+m
n
i
C
∗
ij
P
R
n
j
, where C
ij
=
3
c=1
U
ν
ci
U
ν∗
cj
[4,21].
The couplings relating with G
±
W
are proved the same way, namely
Y
ν,aI
e
L,a
N
R,I
G
−
W
=
√
2
v
(M
D
)
aI
e
L,a
N
R,I
G
−
W
=
g
√
2m
W
U
ν∗
ai
e
a
P
R
n
i
G
−
W
.
The vertices relating to LFVHD are collected in Table 1. We note that the coupling hG
+
W
G
−
W
in
Table 1 is consistent with that given in [8,25].
The effective Lagrangian of the LFVHD is written as L
LF V
= h
(
L
μP
L
τ +
R
μP
R
τ
)
+
h.c., where
L,R
are scalar factors arising from loop contributions. The partial decay width is
2
We thank Dr. E. Arganda for showing us this point.