In the following section I discuss the Higgs sector of the Composite Higgs model. In this section we consider a general nature of the composite Higgs model where the symmetry in the strong interaction sector is G. We assume that the global symmetry G is dynamically broken to the subgroup H at the strong scale f ∼ TeV. And, we assume the subgroup H0 ⊂ G is gauged by external gauge bosons. In the symmetry breaking pattern G → H, n=dim(G)−dim(H) degrees of freedom become the Goldstone bosons. Among those the Goldstone bosons n0 = dim(H0)− dim(H1) are eaten by the elementary gauge bosons, where H1 = H ∩H0 is the unbroken gauge symmetry after the EWSB. Then, the n−n0
Goldstone bosons become the physical Higgs bosons. In Fig. 11, we represent this condition of the composite sector by a simple cartoon.
For realistic model, we have to impose several conditions on the above idea of the strong dynamics. The first, the subgroup H have to contain the SM electroweak gauge symmetry as H ⊃ GSM = SU(2)L×U(1)Y. The second, the coset space G/H have to contain at least oneSU(2)L doublet Goldstone boson, which become the physical Higgs boson and the eaten Goldstone bosons. The third, the strong sector have to have a custodial symmetry to prevent from large contributions of the Peskin-Takeuchi T parameter and Zb¯b corrections.
When we take into account these conditions, the minimal model is G=SO(5), H =SO(4) and H0 =GSM. 1
A. Minimal Composite Higgs model
In this section, we consider the minimal symmetry breaking pattern SO(5) → SO(4) ∼ SU(2)L×SU(2)R at the strong scale f ∼ TeV. And, the SM subgroup SU(2)L×U(1)Y
of H is gauged. The coset space SO(5)/SO(4) corresponds to four real Goldstone bosons, which transform as a 4 of the SO(4). Among them, one Goldstone boson is the physical Higgs boson and the others are eaten by the three gauge bosons so that there is no extra physical Higgs bosons. We introduce an extra global U(1)X for the correct hyper charges
1 In the paper [4], the composite Higgs model is considered with the global symmetryG=SU(3)L. However, in this case, the model does not have the custodial symmetry. Therefore,T parameter andZb¯bcorrections are large and allowed regions are very small.
H1 H H0
G →H n elementary
sector
sector composite
n0
Higgs
FIG. 11: A general condition of symmetry breaking in the composite sector. In this thesis we consider the minimal model, G=SO(5), H =SO(4) and H0 =SU(2)×U(1)Y. In the condition n= 4, n0 = 3 and one physical Higgs boson.
of the composite fermions. The hypercharges of the composite fermions are obtained by Y =TR3+X. The composite Higgs models of these set-up are called the Minimal Composite Higgs Model (MCHM).
The four Goldstone bosons can be parametrized by the broken generatorsTˆa(ˆa= 1 ∼4) of the coset space SO(5)/SO(4) and the four real scalars haˆ. From the nonlinear sigma model, the Goldstone matrix Σis given by
Σ=Σ0eΠ/f, Σ0 = (0,0,0,0,1), Π=−iTˆahˆa√
2, (68)
where
(Tˆa)ij =− i
√2(δiˆaδi5−δajˆδ5i). (69) Then, the Σ can be written by
Σ= sinh/f
h (h1, h2, h3, h4, hcoth/f), h= /"
(hˆa)2. (70) In the unitary gauge the vacuum expectation value (VEV) can be aligned to the any direction by a SO(4) rotation. If we identify theh4 with the physical Higgs bosonH, theΣ
is given by
Σ=Σ0U (71)
=Σ0
⎛
⎜
⎜
⎜
⎝
13 0 0
0 cosH/f sinH/f 0 −sinH/f cosH/f
⎞
⎟
⎟
⎟
⎠
(72)
= (0,0,0,sinH/f ,cosH/f), (73)
where we define the matrix U for later convenience.
B. The effective Lagrangian of the gauge sector
Before discussing the explicit models, we consider the effective Lagrangian of the MCHM after integrating out the resonances of the composite sector. This procedure is useful to study properties of the composite Higgs model based on the symmetry and to calculate the loop induced Higgs potential in following section. At first, we consider the effective Lagrangian of the gauge sector. For convenience, we assume that the global symmetry SO(5)×U(1)X
is gauged by introducing extra non-dynamical gauge bosons. Then, we can derive a general SO(5)×U(1)X invariant effective action of the SM gauge bosons. After integrating out the particles which are heavy due to the strong dynamics the effective Lagrangian of the gauge bosons at the quadratic level is given by
Lgaugeeff = 1
2PTµν[ΠX0 (p)XµXν +Π0(p)Tr(AµAν) +Π1(p)ΣAµAνΣT], (74) wherePTµν =ηµν−pµpν/p2 andXµis the U(1)X gauge boson andAµ=AaµTa+AˆaµTˆa is the SO(5) gauge bosons of the unbroken and the broken generators. The unbroken generators (TL,Ra )ij (a= 1,2,3, i, j = 1, ...,5) are given by
(TLa)ij =−i 2
%1
22abc(δibδcj −δjbδic) +δiaδj4−δi4δja( , (TRa)ij =−i
2
%1
22abc(δibδcj −δjbδic)−δiaδj4+δi4δja( ,
(75)
where L, R mean the symmetry SO(4) ∼ SU(2)L×SU(2)R. The broken generators are Eq. 69. The form factors Π0,1,ΠX0 come from the strong dynamics, and we can not pertur-batively calculate within the 4D effective theory. We can perturbatively calculate the form
factors in the 5D Adsmodel or the deconstructed 4D model. The poles of the form factors are gauge resonances. The form factors contain effects of mixings between the elementary and the composite gauge bosons. When we expand on theSO(4) preserving vacuumΣ=Σ0, the effective action can be written by
Lgaugeeff = 1
2PTµν[ΠX0 (p)XµXν +Πa(p)AaµAaν +Πˆa(p)AˆaµAˆaν] (76) whereΠa=Π0,Πˆa =Π0+Π1/2 are the form factors of the unbroken and broken generators.
In the large N expansion the Πa, Πˆa are written by an infinite sum of resonances, Πa =p2"
n
fρn
p2+m2ρn Πˆa =p2"
n
fan
p2+m2an +1
2f2, (77)
where mρn, man are masses of the gauge resonances at n-th level of 6-plet and 4-plet of SO(4), while fρn and fan are decay constants of the gauge resonances respectively. Then, the Π0,Π1 at the zero momentum are given by
Π0(0) =ΠX0 (0) = 0, Π1(0) =f2. (78) By using Eq. 73 and 74 and disappearing the non-dynamical gauge bosons, the effective Lagrangian of the elementary gauge bosons are given by
Lgaugeeff = 1 2PTµν%#
ΠX0 (p) +ΠX0 (p)) + sin2(H/f)
4 Π1(p)$ BµBν
+#
Π0(p) + sin2(H/f)
4 Π1(p)$
AaµAaν + 2 sin2(H/f)Π1(p) ˆH†TaYHAˆ aµBν
(,
(79)
where Aaµ, Bµ are SU(2)L×U(1)Y gauge bosons and ˆH is defined as Hˆ = 1
h
⎛
⎝
h1−ih2 h3−ih4
⎞
⎠. (80)
The ˆHt = (0,1) when the Higgs vev is aligned along the h3 direction by a SO(4) rotation.
When we expand the form factors at small momenta and use Eq. 78, the effective Lagrangian is given by
Lgaugeeff = 1 2PTµν%1
2
#f2sin2(⟨H⟩/f) 4
$
(BµBν +Wµ3Wν3−2Wµ3Bν) +#f2sin2(⟨H⟩/f)
4
$Wµ+Wν− + p2
2 [Π′0(0)WµaWνa+ (Π′0(0) +ΠX0 ′(0))BµBν] +...( .
(81)
Therefore, relations among the form factors and the gauge couplings are given by 1
g2 =−Π′0(0), 1
g′2 =−(Π′0(0) +ΠX0 ′(0)). (82) .
The Higgs bosons kinetic terms for canonical normalization of gauge boson given by LHiggskin = f2
2 (DµΣ)(DµΣ)T, DµΣ=∂µΣ+WµaΣTLa+BµΣTR3, (83)
= 1
2∂µH∂µH+ g2f2
4 sin(H/f)(Wµ+Wµ−+ 1
2 cos2θWZµZµ). (84) When we expand the Higgs boson around the vevH → ⟨H⟩+H, we obtain
f2
4 sin(H/f) = f2[sin2(⟨H⟩/f) + 2 sin(⟨H⟩/f) cos(⟨H⟩/f)(H/f) + (1−2 sin2(⟨H⟩/f)(H/f)2+...]
=v2+ 2v7
1−ξH+ (1−2ξ)H2+...,
(85)
where ξ=v2/f2. Therefore, the Higgs vev is given by v =fsin⟨H⟩
f = 246 GeV. (86)
and the Higgs couplings to the gauge bosons V =W, Z are given by gHV V =gHV VSM 7
1−ξ gHHV V =gHHV VSM 7
1−2ξ. (87)
Therefore, deviations of the Higgs coupling with the SM massive gauge bosons depend on only the strong breaking scale f.
C. The effective Lagrangian of the fermion sector
Next, we consider the effective Lagrangian of fermions. The effective Lagrangian of fermion depends on representations under the global symmetry G of the composite sector.
Main contributions to the loop induced Higgs potential come from the top sector since the compositeness of the top sector is large. Therefore, the dependence on the representation in the effective Lagrangian of the 3rd generation is important for the EWSB. And, properties of the Higgs couplings different among the representations.
At first, we consider the4(spinor) representation. This choice is minimal in the composite Higgs model of the SO(5)/SO(4) coset space and called MCHM4. Like the gauge boson
case we embed the elementary fermions qL, uR, dR in spinor representations of SO(5) with non-dynamical fields. The spinor representation of SO(5) consists of SU(2)L and SU(2)R
doublets. The spinor representations can be written by
Ψ4q =
⎡
⎣ qL
QL
⎤
⎦, Ψ4u =
⎡
⎢
⎢
⎢
⎣ quR
⎛
⎝ uR
d′R
⎞
⎠
⎤
⎥
⎥
⎥
⎦
, Ψ4d=
⎡
⎢
⎢
⎢
⎣ qRd
⎛
⎝ u′R dR
⎞
⎠
⎤
⎥
⎥
⎥
⎦
, (88)
where the U(1)X charge of these fields are 1/6. Then, the fermion effective Lagrangian of the spinor representation is given by
Lf ermion(4)
ef f = "
r=q,u,d
Ψ¯4r ̸p[Πr0(p) +Πr1(p)ΓiΣi]Ψ4r+ "
r=u,d
Ψ¯4q[M0r(p) +M1r(p)ΓiΣi]Ψ4r, (89) where
ΓiΣi =
⎛
⎝
1cos(H/f) σˆsin(H/f) ˆ
σ†sin(H/f) −1cos(H/f),
⎞
⎠ σˆ ={−→σ,−i1}Hˆa/H (90) and Πr0,1, M0,1r are form factors of the composite fermions. The form factors contain effects of mixings between the elementary fields and the composite fields. By setting the non-dynamical fields are zero, the effective Lagrangian of the qL, uR, dR is given by
Lf ermion(4)
ef f = ¯qL ̸p(Πq0(p) +Πq1(p) cos(H/f))qL+ ¯uR ̸p(Πu1(p)−Πu1(p) cos(H/f))uR
+ ¯dR̸p(Πu1(p)−Πu1(p) cos(H/f))dR
+ sin(H/f)M1u(p)¯qLHuR+ sin(H/f)M1d(p)¯qLHdR+h.c.
(91)
After normalizing the kinetic term, we approximately obtain fermion masses of the4 repre-sentation m4u,d at the low energy limit p→0
m4u,d ∼ M1u,d(0) /Zq4Zu,d4
shch ∼ M1u,d(0) /Zq4Zu,d4
v
f, (92)
where Zq4 = Πq0(0) + chΠq1(0) and Zu,d4 = Πu,d0 (0) − chΠu,d1 (0), sh = sin(H/f) and ch = cos(H/f). By expanding Lf ermion(4)
ef f we obtain approximately deviations of the Higgs couplings to the fermions like the gauge bosoms
gHf f =gHf fSM 7
1−ξ. (93)
The allowed parameter regions of the model compatible with current precision measurements is very small from the Zb¯b corrections. Therefore, we don’t consider this model in the following.
Next, we consider the 5(fundamental) representation of SO(5). This model is called the MCHM5. The 5 representation is written by 4 and 1 in the SO(4) language, 5 = 4⊕1.
In the MCHM5 we can not simultaneously generate bottom and top quark masses by one U(1)X charge. We introduce four fundamental multiplets Ψ5q1(X = 2/3),Ψ5q2(X = −1/3), Ψ5u(X = 2/3) and Ψ5d(X = −1/3) with another U(1)X charge for this purpose. The top quark mass term is generated by mixing between Ψ5q1(X = 2/3) and Ψ5u(X = 2/3). On the other hand, the bottom quark mass term is generated by mixing between Ψ5q2(X =−1/3) and Ψ5d(X = −1/3). We embed the elementary fields into the 5 representation with non-dynamical fields.
Ψ5q1 =
⎡
⎢
⎢
⎢
⎣
⎛
⎝ q′1L
qL
⎞
⎠
u′L
⎤
⎥
⎥
⎥
⎦
Ψ5q2 =
⎡
⎢
⎢
⎢
⎣
⎛
⎝ qL
q2L′
⎞
⎠
d′L
⎤
⎥
⎥
⎥
⎦
Ψ5u =
⎡
⎢
⎢
⎢
⎣
⎛
⎝ qRu q′Ru
⎞
⎠
uR
⎤
⎥
⎥
⎥
⎦
Ψ5d =
⎡
⎢
⎢
⎢
⎣
⎛
⎝ q′dR qRd
⎞
⎠
dR
⎤
⎥
⎥
⎥
⎦
, (94)
where the fields except theqL, uR anddRare non-dynamical fields. The effective Lagrangian of the MCHM5 is given by
Lf ermion(5)
ef f = "
r=q1,q2,u,d
Ψ5r
i ̸p(δijΠr0(p) +ΣiΣjΠr1(p))Ψ5r
j + ¯Ψ5q1i(δijM0u(p) +ΣiΣjM1u(p))Ψ5uj
+ ¯Ψ5q2i(δijM0d(p) +ΣiΣjM1d(p))Ψ5dj +h.c.
(95) By expanding the Lagrangian, we obtain the effective Lagrangian of the elementary fields qL, uL and dR,
Lf ermion(5)
ef f = ¯qL ̸p[Πq10 (p) +Πq20 (p) + s2h
2(Πq11 (p) +Πq21 (p))]qL
+ ¯uR̸p(Πu0(p) +c2hΠu1(p))uR+ ¯dR ̸p(Πd0(p) +c2hΠd1(p))dR
+shch
√2 (¯qLM1u(p)uR+ ¯qLM1ddR) +h.c.,
(96)
where the form factors contain the effects of the mixing between the elementary and the composite sector. Then, the SM fermion masses m5u,d is approximately given by
m5u,d ∼ shch
√2
M1u,d(0)
/Zq5Zu,d5 ∼ M1u,d(0) /2Zq5Zu,d5
v
f, (97)
where Zq5 =Πq10 (0) +Πq20 (0) +s22h(Πq11 (0) +Πq21 (0)), Zu,d5 =Πu,d0 (0) +c2hΠu,d1 (0).
By using the m5u,d we can discuss the yukawa coupling. The form factors can be decom-posed in the SO(4) representations and given by
Πq10 (p) = 1 +ΠqQ14(p), Πq20 (p) = 1 +ΠqQ24(p), Πq11 (p) =ΠqQ11(p)−ΠqQ14(p),Πq21 (p) = ΠqQ21(p)−ΠqQ24(p), Πu0(p) = 1 +ΠuQ4(p), Πu1(p) =ΠuQ1(p)−ΠuQ4(p), Πd0(p) = 1 +ΠdQ4(p),
Πd1(p) =ΠdQ1(p)−ΠdQ4(p),
M1u(p) =MQu1(p)−MQu4(p), M1d(p) = MQd1(p)−MQd4(p),
(98) where by large N expansion the form factors under theSO(4) symmetry are given by
ΠqQ14,1,q2(p) ="
n
|fQq14,1,q2|2 p2+ (mu,d
Q(n)4,1)2, Πu,dQ4,1(p) ="
n
|fQu,d4,1|2 p2+ (mu,d
Q(n)4,1)2, MQu,d4,1(p) ="
n
fQq14,1,q2fQu,d4,1mu,d
Q(n)4,1
p2+ (mu,d
Q(n)4,1)2 .
(99)
The mu,d
Q(n)4,1 is fermion resonance masses and the fQq14,1,q2, fQu,d4,1 corresponds to elementary-composite mixing mass parameters. We take into account only the lightest resonances in each representation of SO(4), mu,d
Q(n)4,1 = Mu54,1,d4,1. And, we define fQq14 = fQq11 = y5uLf, fQq24 = fQq21 = ydL5 f, fQu4 = fQu1 =yuR5 f, fQd4 = fQd1 = y5dRf. These notations will be used in the fol-lowing discussions of phenomenologies. Then, deviations of the yukawa couplings are given by
y5u m5u = 1
m5u
∂m5u
∂v = 2
ftan(2v/f) + f
2Zq5Zu5R sin(2v/f)%, 1
|Mu54|2 − 1
|Mu51|2 .
(|yuL5 |2/2−|yuR5 |2) +
, 1
|Md54|2 − 1
|Md51|2 .
|y5dL|2/2− f2|yuR5 |2 2
, 1
|Mu54|2 − 1
|Mu51|2
. ,|y5uL|2
|Mu54|2 + |ydL5 |2
|Md54|2 .(
, yd5
m5d = 1 m5d
∂m5d
∂v = 2
ftan(2v/f)+ f
2Zq5Zd5R sin(2v/f)%, 1
|Mu54|2 − 1
|Mu51|2 .
|yuL5 |2/2 +
, 1
|Md54|2 − 1
|Md51|2 .
(|y5dL|2/2−|y5dR|2)− f2|ydR5 |2 2
, 1
|Md54|2 − 1
|Md51|2
. ,|yuL5 |2
|Mu54|2 + |ydL5 |2
|Md54|2 .(
. (100) The deviations of the yukawa couplings in the first order is given by
2
ftan(2v/f) = 1−2ξ
√1−ξ. (101)
The contributions from the second order can be large in typical relations among the elementary-composite mixing parameters and resonance masses. The deviation from the first order approximation may be measured at the ILC. I discuss about the yukawa cou-plings more precisely in the following sections. In the 5 representation corrections of the EWPT are relatively small. Therefore, in the following section, we discuss phenomenolo-gies of the 5 representation in detail with the explicit SO(4) fermion resonances and the elementary-composite mixings.
Finally, we consider the 10 (anti-symmetric) representation. This model is called the MCHM10. In the SO(4), the 10 representation is written by 4 and 6, 10 =4⊕6. In the MCHM10 the masses of the up-type quark and bottom-type quark can be simultaneously generated by one U(1)X charge X = 2/3. The elementary fields embedded on the 10 representation of SO(5) are given by
Ψ10q = 1 2
⎛
⎜
⎜
⎜
⎜
⎜
⎜
⎜
⎜
⎝
dL
−idL
0
uLiuL
dL idL uL −iuL 0
⎞
⎟
⎟
⎟
⎟
⎟
⎟
⎟
⎟
⎠
, Ψ10u = 1 2
⎛
⎜
⎜
⎜
⎜
⎜
⎜
⎜
⎜
⎝
−uR
uR
uR 0
−uR
0 0
⎞
⎟
⎟
⎟
⎟
⎟
⎟
⎟
⎟
⎠ ,
Ψ10d = 1 2
⎛
⎜
⎜
⎜
⎜
⎜
⎜
⎜
⎜
⎝
i√dR2 −d√R2
dR
√2 id√R2
−i√dR2 −d√R2 0
dR
√2 −id√R2
0 0
⎞
⎟
⎟
⎟
⎟
⎟
⎟
⎟
⎟
⎠ .
(102)
where the non-dynamical fields have already been vanished. The effective Lagrangian of the MCHM10 is given by
Lf ermion(10)
ef f = "
r=q,u,d
[Tr( ¯Ψ10r ̸pΠr0(p)Ψ10r ) +ΣΨ¯10r ̸pΠr1(p)Ψ10r ΣT] + "
r=u,d
[Tr( ¯Ψ10q Mr0(p)Ψ10r ) +ΣΨ¯10q Mr1(p)Ψ10r ΣT] + h.c.
(103)
By expanding, we obtain the effective Lagrangian of the dynamical fields, Lf ermion(10)
ef f = ¯uL ̸p[Πq0(p) + (c2h 2 +s2h
4)Πq1(p)]uL
+ ¯dL̸p[Πq0(p) + c2h
2Πq1(p)]dL + ¯uR ̸p(Πu0(p) + s2h
4 Πu1(p))uR+ ¯dR ̸p(Πd0(p) + s2h
4Πd1(p))dR
−shch
4 q¯LM1u(p)uR− shch
2√
2q¯LM1ddR
(104)
The fermion masses m10u,d are approximately given by m10u ∼ shch
4
M1u(0)
7Zu10LZu10R, m10d ∼ shch
2√ 2
M1d(0) /Zd10LZd10R
(105)
whereZu10L =Πq0(0)+(c22h+s42h)Πq1(0),Zd10L =Πq0(0)+c22hΠq1(0) andZu10R,dR =Πu,d0 (0)+s42hΠu,d1 (0).
The form of the top and bottom masses is different from that of the 5 representation.
LIke the 5 we discuss the yukawa couplings in the 10. The form factors can be decom-posed in the SO(4) representations,
Πq0(p) = 1 +ΠqQ6(p), Πu0(p) = 1 +ΠuQ6(p), Πq1(p) = 2(ΠqQ4(p)−ΠqQ6(p)),
Πu1(p) = 2(ΠuQ4(p)−ΠuQ6(p)), Πd0(p) = 1 +ΠdQ6(p),Πd1(p) = 2(ΠdQ4(p)−ΠdQ6(p)), M1u(p) = 2(MQu4(p)−MQu6(p)), M1d(p) = 2(MQd4(p)−MQd6(p)),
(106)
where by large N expansion the form factors under theSO(4) symmetry are given by ΠqQ4,6(p) ="
n
|fQq4,6|2 p2+ (mQ(n)
4,6)2, Πu,dQ4,6(p) ="
n
|fQu,d4,6|2 p2+ (mQ(n)
4,6)2, MQu,d4,6(p) ="
n
fQq4,6fQu,d4,6mQ(n)
4,6
p2+ (mQ(n) 4,6)2 .
(107)
We take into account the lightest modes of themQ(n)
4,6 =M4,610. When we define fQq4 =fQq6 = y10Lf, fQu4 = fQu6 = y10uRf, fQd4 = fQd6 = y10dRf, deviations of the yukawa couplings in the 10
representation are given by yu10
m10u = 1 m10u
∂m10u
∂v = 2
ftan(2v/f) + f
4Zu10LZu10R sin(2v/f)%, 1
M4102 − 1 M6102
.
(yL102−y10uR2)
− f2yL102yuR102 2
, 1
M4102 − 1 M6102
.2
(, yd10
m10d = 1 m10d
∂m10d
∂v = 2
ftan(2v/f) + f
2Zd10LZd10R sin(2v/f)%, 1
M4102 − 1 M6102
.
(yL102−ydR102/2)
− f2yL102ydR102 2
, 2
M4104 + 1
M6104 − 1 M4102M6102
.( ,
(108) where the approximation of the first order is the same as the 5 represantation. We also discuss phenomenologies of the10representation with the explicitSO(4) fermion resonances in the following section.