扩展Exo-Higgs模型中的不对称暗物质研究

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"Asymmetric dark matter in extended exo-Higgs scenarios" 在本文中，研究者探讨了一个扩展的Exo-Higgs模型，该模型引入了一个新的单重复合标量粒子χ，以此来实现不对称暗物质（Asymmetric Dark Matter, ADM）的概念。Exo-Higgs模型是一个超越标准模型的理论框架，它提供了电弱重生机制的替代方案，从而避免了标准模型中的一些固有问题。在标准模型中，电弱重生是一种可能解释宇宙中观察到的物质-反物质不对称性的机制。然而，这个过程通常难以实现，因为它需要在电弱相变过程中保持CP对称性的破坏，并且需要极端的条件。Exo-Higgs模型则通过引入额外的物理实体，为这个过程提供了一种新的可能性。在扩展的Exo-Higgs模型中，新粒子χ不仅是ADM的一个潜在候选者，而且它的质量被预测在大约1.3GeV以上。这一预测基于模型的理论计算和宇宙学约束，尤其是需要确保χ能够有效地参与暗物质的相互作用，以维持宇宙中暗物质和普通物质的比例。关键的一点是，χ粒子具有亲脂性（leptophilic）耦合，这意味着它倾向于与轻子而不是夸克相互作用。这种特性对于ADM的消除至关重要，因为它允许χ粒子与宇宙中的轻子对有效地湮灭，从而调整暗物质的密度，使其与观测值相符。同时，这种耦合也可能影响到大型强子对撞机（Large Hadron Collider, LHC）上可能的探测信号。在LHC实验中，χ粒子的生产和衰变过程将为物理学家提供寻找这种新型暗物质粒子的线索。研究者分析了这些过程，预测了可能的衰变模式以及与标准模型粒子的相互作用，这些信息对于设计实验策略和数据分析至关重要。通过对χ粒子的探测，不仅有可能验证Exo-Higgs模型，而且还能进一步揭示宇宙中的物质-反物质不对称性是如何产生的。这篇论文深入研究了扩展的Exo-Higgs模型在不对称暗物质框架下的应用，提出了一种可能的电弱重生替代机制，并预测了在LHC上寻找新粒子的实验迹象。这一工作为理解宇宙的暗物质成分及其与标准模型之间的关系提供了新的理论视角。

Physics Letters B 772 (2017) 512–516

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Asymmetric dark matter in extended exo-Higgs scenarios

Hooman Davoudiasl

, Pier Paolo Giardino

a,∗

, Cen Zhang

a,b

Department of Physics, Brookhaven National Laboratory, Upton, NY 11973, USA

Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China

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

Article history:

Received

20 April 2017

Received

in revised form 8 June 2017

Accepted

5 July 2017

Available

online xxxx

Editor:

G.F. Giudice

The exo-Higgs model can accommodate a successful baryogenesis mechanism that closely mirrors

electroweak baryogenesis in the Standard Model, but avoids its shortcomings. We extend the exo-Higgs

model by the addition of a singlet complex scalar χ . In our model, χ can be a viable asymmetric dark

matter (ADM) candidate. We predict the mass of the ADM particle to be m

≈ 1.3GeV. The leptophilic

couplings of χ can provide for eﬃcient annihilation of the ADM pairs. We also discuss the LHC signals

of our scenario, and in particular the production and decays of exo-leptons which would lead to “lepton

pair plus missing energy” ﬁnal states. Our model typically predicts potentially detectable gravitational

waves originating from the assumed strong ﬁrst order phase transition at a temperature of ∼ TeV. If the

model is further extended to include new heavy vector-like fermions, e.g. from an ultraviolet extension,

χ couplings could explain the ∼ 3.5σ muon g − 2anomaly.

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

1. Introduction

In Ref. [1], we introduced the exo-Higgs η associated with

breaking a new SU(2)

gauge interaction that we dubbed exo-

spin [since

the Standard Model (SM) particles do not carry SU(2)

charge and this force is outside the SM]. The model included

fermions, exo-quarks Ϙ and exo-leptons , that can be assigned

SM baryon (B) and lepton (L) numbers, respectively. The quan-

tum

numbers of the exo-fermions were chosen in a way that leads

to a B − L anomaly under SU(2)

gauge interactions. Therefore, by

choosing the parameters of the model to ensure a ﬁrst order phase

transition, the model could potentially accommodate the genera-

tion

of a B − L asymmetry 

B−L

in the early universe, through

the action of SU(2)

exo-sphalerons. This B − L asymmetry would

not be washed out by the SM sphalerons and can hence remain to

become the baryon asymmetry of the universe (BAU).

The

above exo-baryogenesis scenario could be realized in close

analogy with how baryogenesis could have worked in the SM, if

the electroweak phase transition were strongly ﬁrst order and CP

violating

effects were more than ∼ 10

larger (see Ref. [2], for

example). However, the exo-spin sector in Ref. [1] can potentially

accommodate the requisite ﬁrst order phase transition and sig-

Corresponding author.

E-mail

addresses: hooman@bnl.gov (H. Davoudiasl), pgiardino@bnl.gov

(P.P. Giardino),

cenzhang@ihep.ac.cn (C. Zhang).

niﬁcant CP violating effects to yield successful generation of the

observed BAU.

this work, we minimally extend the exo-Higgs model [1] by

adding a singlet complex scalar χ which carries a good global

symmetry. The addition of χ removes ad hoc mass scales that ap-

peared

in the original exo-Higgs model and replaces them with

the Yukawa couplings of χ to charged exo-leptons and SM lep-

tons.

This scalar can be stable and provide a viable asymmetric

dark matter (ADM) candidate [3–6]. We will show that, at typical

strengths, the new Yukawa couplings of χ can mediate the annihi-

lation

of χχ

∗

symmetric population in the early Universe, which

is a requirement for establishing the correct ADM abundance. The

above new Yukawa coupling leads to prompt decays of the exo-

leptons

into SM leptons. These decays transfer the high scale B −L

asymmetry

generated during the SU(2)

phase transition to the

SM sector (see also Ref. [7] for a proposal which includes some

ingredients similar to those in our work).

Since

the Yukawa couplings of χ to exo-leptons and charged

leptons are responsible for both the transfer of 

B−L

and effective

annihilation of χχ

∗

pairs, as mentioned before, at least one of

the exo-leptons  is required to have a mass  1TeV. Given the

requisite non-zero electric charge of the exo-leptons, their produc-

tion

at the LHC can go through Drell–Yan processes and lead to

striking large-missing-energy-plus-charged-lepton signals. Hence,

key interactions involved in our baryogenesis proposal, namely the

aforementioned Yukawa couplings of χ , may potentially be acces-

http://dx.doi.org/10.1016/j.physletb.2017.07.009

0370-2693/

SCOAP

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