750 GeV双光子过量：隐性U（1）规范对称性与大动态混合的解释

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"隐藏的U（1）规范对称性中的双光子过量与大的动力学混合" 在粒子物理学领域，U（1）规范对称性是量子场论中的一个基本概念，它涉及到电荷守恒和电磁相互作用。在这个研究中，作者探讨了一个隐藏的U（1）规范对称性，这种对称性不直接与标准模型中的U（1）Y（弱超荷）对称性相联系，但通过一种称为动力学混合的现象与之交互。这种混合使得新的物理效应可以体现在标准模型的观测中，特别是通过双光子通道。 750 GeV双光子过量是一个引人注目的现象，它在大型强子对撞机（LHC）的数据中被观察到。这个异常可能预示着新物理学的存在，因为它不能用标准模型中的已知粒子解释。作者提出，这个过量可以由带有隐性U（1）规范对称性的新粒子，如类似矢量的夸克和带电的隐性费米子来解释。这些新粒子具有较大的耦合常数，使得它们与标准模型中的粒子有显著的相互作用。关键的是，随着大的动力学混合，标准模型的三个规范群（SU(3)C色力，SU(2)L弱力，U(1)Y电磁力）的耦合在大约10^17 GeV的能量尺度上可能实现统一，这是大统一理论（GUT）的一个可能标志。大统一理论试图将所有基本力统一在一个单一的理论框架内，而不会导致过快的质子衰变，这是GUT模型面临的一个重要挑战。在这种情景下，除了双光子信号外，还预测了一些其他的对撞机特征。例如，存在带有光子并缺失横向动量的事件，其横截面与双光子过量的横截面有关。此外，由于新粒子的衰变，可能会出现三光子和四光子的信号，这些也是寻找新物理学的重要线索。为了避免与奇异稳定带电粒子的观测限制相冲突，作者还讨论了多种策略。这些可能的对撞机信号和宇宙学效应提供了进一步验证这种模型的机会。通过实验探测这些预测的信号，科学家们可以更深入地了解隐藏的U（1）规范对称性，以及它如何影响我们理解宇宙的基本结构。这项研究提供了一个新颖的框架来解释LHC数据中的未解谜团，并提出了一个新的粒子物理模型，其中包含的隐藏U（1）对称性和动力学混合可能开启了一扇通往超出标准模型的新物理世界的大门。这样的理论不仅有助于解释已有的观测，也为未来的粒子物理学研究提供了新的探索方向。

Physics Letters B 760 (2016) 486–493

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Diphoton excess from hidden U(1) gauge symmetry with large kinetic

mixing

Fuminobu Takahashi

a,b

, Masaki Yamada

, Norimi Yokozaki

a,∗

Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan

Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan

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

Article history:

Received

28 April 2016

Received

in revised form 5 July 2016

Accepted

6 July 2016

Available

online 9 July 2016

Editor:

J. Hisano

We show that the 750 GeV diphoton excess can be explained by introducing vector-like quarks and

hidden fermions charged under a hidden U(1) gauge symmetry, which has a relatively large coupling

constant as well as a signiﬁcant kinetic mixing with U(1)

. With the large kinetic mixing, the standard

model gauge couplings unify around 10

GeV, suggesting the grand uniﬁed theory without too rapid

proton decay. Our scenario predicts events with a photon and missing transverse momentum, and its

cross section is related to that for the diphoton excess through the kinetic mixing. We also discuss

other possible collider signatures and cosmology, including various ways to evade constraints on exotic

stable charged particles. In some cases where the 750 GeV diphoton excess is due to diaxion decays, our

scenario also predicts triphoton and tetraphoton signals.

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

1. Introduction

The diphoton excess with an invariant mass around 750 GeV

was

recently reported by the ATLAS [1] and CMS [2] collaborations;

for a spin-0 particle with a narrow width approximation, the local

signiﬁcance is estimated to be 3.9σ and 2.9σ , respectively. While

more data is certainly needed to conﬁrm if the signal is real or

just a statistical ﬂuke, its high statistical signiﬁcance in the clean

analysis using photons triggered enthusiasm and exuberance for

the new physics beyond the standard model (SM), followed by the

appearance of many theoretical papers.

Among

various models proposed so far, the simplest one is

to include a gauge singlet (pseudo)scalar coupled to vector-like

quarks and/or leptons (see e.g. Refs. [3–5] for the early works).

In this model, the (pseudo)scalar is produced via gluon fusion and

decays into a pair of photons through one-loop diagrams with the

extra quarks/leptons running in the loop. The diphoton excess can

be explained if the product of the production cross section times

branching ratio to two photons is in the range of 5–10 fb. This

gives a preference to a relatively large branching fraction to dipho-

Corresponding author.

E-mail

address: yokozaki@truth.phys.tohoku.ac.jp (N. Yokozaki).

It is still a puzzle why such a (pseudo)scalar coupled to gluons and photons

exists in nature. One possible answer is to relate it to the QCD axion (or its bosonic

partner, saxion) which solves the strong CP problem [6–9].

tons, which necessitates either multiple extra matter ﬁelds and/or

large hypercharges (Y  1) of the extra ﬁeld running in the loop.

this paper we consider a possibility that the large hyper-

charges

are originated from unbroken hidden U(1)

gauge symme-

try

which has a relatively strong gauge coupling and a signiﬁcant

kinetic mixing with U(1)

. Then, hidden fermions acquire large

hypercharges due to the kinetic mixing, and the induced hyper-

charges

are generically irrational. We will show that the diphoton

excess can be explained by the (pseudo)scalar coupled to gluons

and photons though the extra quark/hidden fermion loop dia-

grams.

Our

scenario is based on a rather simple U(1)

extension of

the standard model, which enables us to make a deﬁnite predic-

tion

that can be tested soon at the LHC Run-2. Since the hidden

fermions are charged under U(1)

, the (pseudo)scalar responsible

for the diphoton excess can also decay into γγ



, where γ



denotes

the hidden photon. Thus, our scenario predicts events with a pho-

ton

and missing momentum,

and we will see that its production

cross section times branching fraction is simply related to that for

the diphoton excess through the kinetic mixing. The events with a

photon and missing momentum have been searched for at the LHC

Run-1 [11,12] and Run-2 [13], and there is an upper bound on the

See Ref. [10] for a related work.

http://dx.doi.org/10.1016/j.physletb.2016.07.013

0370-2693/

SCOAP

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