We argue that there are both experimental and theoretical reasons to reconsider the construction of KSVZ-like axion models. From the experimental side, predictions for the axion-photon coupling are not consistent with the collection of astrophysical hints. From the theoretical side, we find that the construction can be conceptually simplified. In particular, it contains an unnecessary assumption on the type of the gauge theory involved which has far-reaching consequences for low energy axion phenomenology. In order to relax this assumption, we allow heavy fermions of the KSVZ-like models to carry magnetic charge. We then show that the axion-photon coupling is generically dominated by the axial anomaly of magnetic currents. Finally, we derive the expression for magnetic anomaly coefficients, which determine the range of numerical values for the axion-photon coupling.
Heavy QCD axions are well-motivated extensions of the QCD axion that address the quality problem while still solving the strong CP problem. Owing to the gluon coupling, critical for solving the strong CP problem, these axions can be produced in significant numbers in beam dump and collider environments for axion decay constants as large as PeV, relevant for addressing the axion quality problem. In addition, if these axions have leptonic couplings, they can give rise to long-lived decay into lepton pairs, in particular, dominantly into muons above the dimuon threshold and below the GeV scale in…
The QCD axion is a leading dark matter candidate that emerges as part of the solution to the strong CP problem in the Standard Model. The coupling of the axion to photons is the most common experimental probe, but much parameter space remains unexplored. The coupling of the QCD axion to the Standard Model scales linearly with the axion mass; therefore, the highly-motivated region 0.4-120 neV, corresponding to a GUT-scale axion, is particularly difficult to reach. This paper presents the design requirements for a definitive search for GUT-scale axions and reviews the technological advances need…
One of the most promising methods to search for axions is a light-shining-through-walls (LSW) experiment. In this work, we discuss the possibility of performing an LSW experiment at the ILC experiment, where photon beams are generated for positron production. The photon beam is energetic and intense; the energy is of order MeV and the number of photons is about $10^{24}$ per year. Due to the high energy and intensity, this LSW experiment can reveal the parameter region of the axion unexplored by previous ground-based experiments.
The QCD axion is a well-motivated addition to the standard model to solve the strong $C\!P$ problem. If the axion acquires mass dominantly from a hidden sector, it can be as heavy as $O(1)$ GeV, and the decay constant can be as low as $O(100)$ GeV without running into the axion quality problem. We propose new search strategies for such heavy QCD axions at the Belle II experiment, where the axions are expected to be produced via $B\to K a$. We find that a subsequent decay $a\to 3π$ with a displaced vertex leads to a unique signal with essentially no background, and that a dedicated search can e…
We study the mirror world with dark matter arising from the thermal freeze-out of the lightest, stable mirror particle -- the mirror electron. The dark matter abundance is achieved for mirror electrons of mass 225 GeV, fixing the mirror electroweak scale near $10^8$ GeV. This highly predictive scenario is realized by an axion that acts as a portal between the two sectors through its coupling to the QCD and mirror QCD sectors. The axion is more massive than the standard QCD axion due to additional contributions from mirror strong dynamics. Still, the strong CP problem is solved by this "heavy" …
We demonstrate that the observed cosmological excess of matter over antimatter may originate from a heavy QCD axion that solves the strong CP problem but has a mass much larger than that given by the Standard Model QCD strong dynamics. We investigate a rotation of the heavy QCD axion in field space, which is transferred into a baryon asymmetry through weak and strong sphaleron processes. This provides a strong cosmological motivation for heavy QCD axions, which are of high experimental interest. The viable parameter space has an axion mass $m_a$ between 1~MeV and 10 GeV and a decay constant $f…
We study phenomenological implications of an axion that arises as a pseudo Nambu-Goldstone boson due to the spontaneous breaking of anomaly-free global flavor symmetry. One interesting possibility for such anomaly-free axion to explain dark matter (DM) is when it has a mass of order keV and an intermediate scale decay constant, since it can be explored through direct search experiments, X-ray observations, various stellar cooling processes, and the misalignment mechanism naturally explains the DM abundance. As a concrete renormalizable model of such axion, we consider an extended Higgs sector …
A connection between flavour anomaly, neutrino mass, and axion
我们提出了一个极小模型，其中味道异常的$b \to s μ^+ μ^-$过渡连接到打破Peccei-Quinn（PQ）对称性。通过引入一代在标准模型规范群下类矢量但在定域$U(1)_X$群下带电的重夸克和重轻子，从新的物理贡献中解释了味反常现象.它们与SM夸克和轻子混合，诱导出改变味道的$Z^\prime$耦合，从而在树水平上产生$b \to s μ^+μ^-$异常。另一方面，新的费米子是手征的整体Peccei-Quinn（PQ）对称。PQ对称性自发破缺产生的赝戈德斯通玻色子成为轴子，解决了强CP问题，并提供了冷暗物质候选者。同样的对称性阻止了右手中微子具有马约拉纳质量项。但是，中微子特有的希格斯偶线的引入允许中微子具有狄拉克质量项而没有微调问题。该模型显示了轴子、中微子、暗物质和味道物理之间的相互作用。
We explore whether the axion which solves the strong CP problem can naturally be much lighter than the canonical QCD axion. The $Z_\mathcal{N}$ symmetry proposed by Hook, with $\mathcal{N}$ mirror and degenerate worlds coexisting in Nature and linked by the axion field, is considered in terms of generic effective axion couplings. We show that the total potential is safely approximated by a single cosine in the large $\mathcal{N}$ limit, and we determine the analytical formula for the exponentially suppressed axion mass. The resulting universal enhancement of all axion interactions relative to …
In the framework where the strong coupling is dynamical, the QCD sector may confine at a much higher temperature than it would in the Standard Model, and the temperature-dependent mass of the QCD axion evolves in a non-trivial way. We find that, depending on the evolution of $Λ_{\mathrm{QCD}}$, the axion field may undergo multiple distinct phases of damping and oscillation leading generically to a suppression of its relic abundance. Such a suppression could therefore open up a wide range of parameter space, resurrecting in particular axion dark-matter models with a large Peccei-Quinn scale $f_…
Detecting the QCD axion via the ferroaxionic force with piezoelectric materials
Perimeter Institute for Theoretical Physics（Perimeter理论物理研究所）；Department of Physics and Astronomy, University of North Carolina（北卡罗来纳大学物理与天文学系）；Center for Fundamental Physics, Department of Physics and Astronomy, Northwestern University（西北大学物理与天文学系基础物理中心）；Kavli Institute for Theoretical Physics, University of California, Santa Barbara（加州大学圣塔芭芭拉分校卡弗里理论物理研究所）；Center for Cosmology and Particle Physics, Department of Physics, New York University（纽约大学物理系宇宙学与粒子物理中心）；Center for Computational Astrophysics, Flatiron Institute（Flatiron研究所计算天体物理学中心）
We review the landscape of QCD axion models. Theoretical constructions that extend the window for the axion mass and couplings beyond conventional regions are highlighted and classified. Bounds from cosmology, astrophysics and experimental searches are reexamined and updated.
CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所理论物理重点实验室）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）；Physics Department, College of Physics and Optoelectronic Engineering, Jinan University（暨南大学物理与光电工程学院物理学系）
Technically Natural Baryogenesis with the QCD Axion
University of California Santa Cruz（加州大学圣克鲁兹分校）；University of Washington（华盛顿大学）；International Centre for Theoretical Physics（国际理论物理中心）；Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Trieste（意大利国家核物理研究所的里雅斯特分部）；University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
We consider hadronic axion models that extend the Standard Model by one complex scalar field and one or more new heavy quarks, i.e. $N_\mathcal{Q} \geq 1$. We review previously suggested selection criteria as well as categorize and catalog all possible models for $N_\mathcal{Q} \leq 9$. In particular, allowing for $N_\mathcal{Q} > 1$ can introduce models that spoil the axion solution of the strong CP problem. Demanding that Landau poles do not appear below some energy scale limits the number of preferred models to a finite number. For our choice of criteria, we find that $N_\mathcal{Q} \leq 28…
