极化e+e-对撞机下，规范-希格斯统一的Z'效应与显著偏差

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在"Physics Letters B" 2017年第775期的一篇文章中，研究者Shuichiro Funatsuka、Hisaki Hatanaka、Yutaka Hosotani、* Yuta Orika探讨了规范-希格斯统一在e+e-对撞机实验中的独特信号。该研究集中在规范-希格斯统一框架下，特别是Kaluza-Klein（KK）激发的中性矢量玻色子（Z'玻色子）对电子正电子湮灭(e+e- → q̄q，其中q代表夸克，包括上、下夸克，以及轻子湮灭过程如μ+μ-）过程的影响。在未来的极化e+e-对撞机实验中，这些Z'玻色子的存在可能导致显著的效应，具体表现在以下几个方面： 1. **σ(μ+μ-)：** 电子正电子对的湮灭截面σ(μ+μ-)会受到Z'玻色子的影响，其能量依赖和极化特性可能偏离标准模型的预测。这表明通过测量σ(μ+μ-)的变化，可以提供对新物理的间接证据。 2. **Lepton Forward-Backward Asymmetry (Rb(μ))**：论文中定义的Rb(μ)，即底夸克对（bb）湮灭截面与μ+μ-过程的比率，也可能显示出显著的偏差。这种差异是由于Z'玻色子特有的干涉效应导致的，可以用来区分标准模型与规范-希格斯统一模型。 3. **Left-Right Asymmetry**：左右不对称性，即在不同极化光子下的反应率差异，也可能在Z'玻色子的参与下发生显著变化。这种特性对于理解粒子间的相互作用以及检验电弱理论的对称性破缺至关重要。文章指出，这些预期的偏差可以作为未来极化e+e-对撞机实验设计的重要参考指标，比如国际直线加速器（ILC）或 Circular Electron Positron Collider (CEPC)等，它们将有助于验证规范-希格斯统一理论，或者在数据中发现超越标准模型的新物理现象。因此，研究结果对于粒子物理学家来说具有重要的实践意义，因为它们为实验探索高能物理领域的深层次规律提供了关键的理论依据。

Physics Letters B 775 (2017) 297–302

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Distinct signals of the gauge-Higgs uniﬁcation in e

−

collider

experiments

Shuichiro Funatsu

, Hisaki Hatanaka

, Yutaka Hosotani

b,∗

, Yuta Orikasa

KEK Theory Center, KEK, Tsukuba, Ibaraki 305-0801, Japan

Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan

Czech Technical University, Prague 12800, Czech Republic

a r t i c l e i n f o a b s t r a c t

Article history:

Received

20 July 2017

Received

in revised form 6 October 2017

Accepted

29 October 2017

Available

online 10 November 2017

Editor:

J. Hisano

Effects of Kaluza–Klein excited neutral vector bosons (Z



bosons) in the gauge-Higgs uniﬁcation on

−

→

qq, 



−

cross sections are studied, particularly in future e

−

collider experiments with

polarized beams. Signiﬁcant deviations in the energy and polarization dependence in σ (μ

−

), the

lepton forward–backward asymmetry, R

(μ) ≡ σ (

bb)/σ (μ

−

) and the left–right asymmetry from the

standard model are predicted.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

With the establishment of the standard model (SM) by the dis-

covery

of the Higgs boson, searching for physics beyond the SM

and understanding the electroweak phase transition have become

a few of the main topics in particle physics. Not only large hadron

colliders, but also e

−

colliders play an important role for this

purpose. In this letter we study distinct signals of the gauge-Higgs

uniﬁcation (GHU) [1–10] in the future e

−

collider experiments.

GHU the Higgs boson is a part of the extra-dimensional com-

ponent

of the gauge potentials, appearing as a ﬂuctuation mode of

an Aharonov–Bohm (AB) phase θ

in the ﬁfth dimension. As a con-

sequence

the Higgs couplings HWW, HZZ and Yukawa couplings

deviate from those in the SM in a universal manner [11].They are

suppressed by a common factor cos θ

;

GHU

HWW

GHU

HZZ

GHU

cos θ

. (1)

For θ

=O(0.1), probable values in the model, the deviation of the

couplings amounts to 1 − cos θ

= O(0.005), and is small. At the

ILC at

√

s = 250 GeV, the ZZH coupling can be measured in the

0.6% accuracy with 2ab

−1

data [12]. Another prominent feature

of the model is that the ﬁrst Kaluza–Klein (KK) excited states of

the neutral gauge bosons, Z



, have large couplings to right-handed

components of quarks and leptons, viable signals of which can be

seen in hadron collider experiments [8,10].

The main purpose of this letter is to check the effect of such



bosons using lepton collider experiments in the past and fu-

Corresponding author.

E-mail

address: hosotani@phys.sci.osaka-u.ac.jp (Y. Hosotani).

ture. We ﬁrst examine the GHU model with precision measure-

ments

in LEP1 experiment at

√

s = M

, and LEP2 experiments for

130 GeV ≤

√

s ≤ 207 GeV. Then we predict several signals of Z



bosons in GHU in e

−

collider experiments designed for future

with collision energy

√

s ≥ 250 GeV with polarized electron and

positron beams.

The GHU model we consider is the SO(5) × U (1)

gauge the-

ory

in the Randall–Sundrum warped space with metric ds

−2k|y|

μν

+ dy

(0 ≤|y| ≤+L) where k is the Ad S

cur-

vature.

The warp factor z

≡ e

is large ( 1). SO(5) symmetry

is broken to SO(4)  SU(2)

× SU(2)

by the orbifold boundary

conditions at y = 0 and L. The SO(5)/SO(4) part of the gauge

ﬁelds, A

(a = 1 ∼ 4), plays the role of the Higgs ﬁeld in the SM.

SU(2)

× U(1)

symmetry is spontaneously broken to U (1)

a brane-localized scalar ﬁeld at y =0. Finally the SU(2)

× U (1)

symmetry is dynamically broken to U (1)

by the Hosotani mech-

anism.

ﬁelds are expanded in KK series. In particular, there are four

KK towers of the neutral vector bosons, γ

(m)

, Z

(m)

, Z

(n)

and A

4(n)

(m = 0, 1, 2, ···, n = 1, 2, 3 ···) where γ

(0)

and Z

(0)

correspond to

the photon and Z boson, respectively. These ﬁelds except for A

couple to the SM ﬁelds and can be observed as neutral Z



vector

bosons.

addition to the quark–lepton multiplets in the vector rep-

resentation

of SO(5), N

dark fermions in the spinor representa-

tion

are introduced. As a consequence the electroweak symmetry

breaking is achieved at the one loop level. The Higgs boson, which

is massless at the tree level, acquires a ﬁnite mass m

, inde-

pendent

of the cutoff scale. The gauge hierarchy problem is thus

solved [2].

https://doi.org/10.1016/j.physletb.2017.10.068

0370-2693/

SCOAP

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