Ultralight axion and modern cosmology tensions
Takeshi Fukuyama
该研究提出弦理论启发的轴子模型，旨在统一解决哈勃张力、随机引力波背景起源及高红移超大质量黑洞过早形成等现代宇宙学难题。
考虑弦理论启发的轴子模型，以全面解决现代宇宙学中的问题，包括哈勃张力问题、随机引力波背景的起源，以及在高红移$z$处超大质量黑洞的过早形成。
String-inspired axion model is considered to comprehensively solve the problems of modern cosmology, Hubble tension problem, the origin of the stochastic gravitational wave background, and too early formation of supermassive black holes at high $z$.
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We study the ultralight axion dark matter with mass around $10^{-22}$ eV in $f(R)$ gravity which might resolve the dark energy problem. In particular, we focus on the fact that the pressure of the axion field oscillating in time produces oscillations of gravitational potentials. We show that the oscillation of the gravitational potential is sensitive to the model of gravity. Remarkably, we find that the detectability of the oscillation through the gravitational wave detectors can be significantly enhanced due to the nonlinear resonance between the ultralight axion and the scalaron.
Ultralight axions are theoretically interesting and phenomenologically rich dark sector candidates, but they are difficult to track across cosmological timescales because of their fast oscillations. We resolve this problem by developing a novel method to evolve them efficiently and accurately. We first construct an exact effective fluid which at late times matches the axion but which evolves in a simple way. We then approximate this evolution with a carefully chosen equation of state and sound speed. With our scheme we find that we can obtain subpercent accuracy for the linear theory suppressi…
The ultralight axion with mass around $10^{-22}$ eV is known as a candidate of dark matter. A peculiar feature of the ultralight axion is oscillating pressure in time, which produces oscillation of gravitational potentials. Since the solar system moves through the dark matter halo at the velocity of about $v \sim 300 \, \text{km} / \text{s} = 10^{-3}$, there exists axion wind, which looks like scalar gravitational waves for us. Hence, there is a chance to detect ultralight axion dark matter with a wide mass range by using laser interferometer detectors. We calculate the detector signal induced…
An ultralight axion around $10^{-23}$ eV is known as a viable dark matter candidate. A distinguished feature of such a dark matter is the oscillating pressure which produces the oscillation of the gravitational potential with frequency in the nano-Hz range. Recently, Khmelnitsky and Rubakov pointed out that this time dependent potential induces the pulse arrival residual and could be observed by the Square Kilometre Array (SKA) experiment. In this paper, we study the detectability of the oscillating pressure of the axion in the framework of $f(R)$ theory, and show that the amplitude of the gra…
The geodetic and frame-dragging effects are the direct consequences of the spacetime curvature near Earth which can be probed from the Gravity probe B (GP-B) satellite. The satellite result matches quite well with Einstein's general relativistic result. The gyroscope of the satellite which measures the spacetime curvature near Earth contains lots of electrons and nucleons. Ultralight axions, vector gauge bosons, and unparticles can interact with these electrons and nucleons through different spin-dependent and spin-independent operators and change the drift rate of the gyroscope. Some of these…
Dynamical mechanisms to generate an ultralight axion of mass $\sim 10^{-21}-10^{-22}$ eV in supergravity and strings are discussed. An ultralight particle of this mass provides a candidate for dark matter that may play a role for cosmology at scales $10\, {\rm kpc}$ or less. An effective operator approach for the axion mass provides a general framework for models of ultralight axions, and in one case recovers the scale $10^{-21}-10^{-22}$ eV as the electroweak scale times the square of the hierarchy with an $O(1)$ Wilson coefficient. We discuss several classes of models realizing this framewor…
We examine the effects of photon-axion mixing on the CMB. We show that if there are very underdense regions between us and the last scattering surface which contain coherent magnetic fields (whose strength can be orders of magnitude weaker than the current bounds), then photon-axion mixing can induce observable deviations in the CMB spectrum. Specifically, we show that the mixing can give rise to non-thermal spots on the CMB sky. As an example we consider the well known CMB cold spot, which according to the Planck data has a weak distortion from a black body spectrum, that can be fit by our mo…
We review the physics case for very weakly coupled ultralight particles beyond the Standard Model, in particular for axions and axion-like particles (ALPs): (i) the axionic solution of the strong CP problem and its embedding in well motivated extensions of the Standard Model; (ii) the possibility that the cold dark matter in the Universe is comprised of axions and ALPs; (iii) the ALP explanation of the anomalous transparency of the Universe for TeV photons; and (iv) the axion or ALP explanation of the anomalous energy loss of white dwarfs. Moreover, we present an overview of ongoing and near-f…
In the context of structure formation with ultralight axion dark matter, we offer an alternative explanation for the mass relation of solitonic cores and their host halos observed in numerical simulations. Our argument is based entirely on the mass gain that occurs during major mergers of binary cores and largely independent of the initial core-halo mass relation assigned to hosts that have just collapsed. We find a relation between the halo mass $M_h$ and corresponding core mass $M_c$, $M_c\propto M_h^{2β-1}$, where $(1-β)$ is the core mass loss fraction. Following the evolution of core masse…
Imprints of ultralight axions on the gravitational wave and pulsar timing measurement
该研究针对超轻类轴子这一暗物质候选者，分析其黑洞超辐射云耗散对中子星-黑洞双星引力波形的影响，对比相关效应并探讨现有与未来空间引力波探测的约束及可探测性。
We reconsider entropy arguments which have been previously argued to support the idea that the dark matter constituents are primordial black holes with many solar masses. It has recently been shown that QCD axions which solve the strong CP problem may have masses $m_a$ in the extended range $10^{-3}eV > m_a > 10^{-33} eV$. Ultralight axions provide so many degrees of freedom that their entropy can exceed that of primordial black holes. This suggests that ultralight axions are more suited than primordial black holes to be constituents of dark matter.
Laboratory constraints on ultralight axion-like particles from precision atomic spectroscopy
本研究利用原子跃迁频率比随时间变化的精密测量，在低质量区获得了对超轻类轴子粒子暗物质的领先实验室约束，并提出后续提升灵敏度的测量方向。
Simulations of multi-field ultralight axion-like dark matter
本研究修改UltraDark.jl代码，首次开展含自相互作用与场间相互作用的双场超轻类轴子暗物质三维模拟，探究了孤子动力学及不同种类孤子碰撞的特性，揭示了多成分、有相互作用情形与单场无相互作用情形的差异。
A number of proposed and ongoing experiments search for axion dark matter with a mass nearing the limit set by small scale structure (${\cal O} ( 10 ^{ - 21 } {\rm eV} ) $). We consider the late universe cosmology of these models, showing that requiring the axion to have a matter-power spectrum that matches that of cold dark matter constrains the magnitude of the axion couplings to the visible sector. Comparing these limits to current and future experimental efforts, we find that many searches require axions with an abnormally large coupling to Standard Model fields, independently of how the a…
Dark gauge sectors and axions are well-motivated in string theory. We demonstrate that if a confining gauge sector gives rise to dark glueballs that are a fraction of the dark matter, and the associated axion has a decay constant near the string scale, then this axion is ultralight and naturally realizes the fuzzy dark matter scenario with a modest tuning of a temperature ratio. Astrophysical observations constrain the size of the glueball component relative to the axionic component, while electric dipole moments constrain mixing with the QCD axion.
Lasing of ultralight axion condensate into photons can be sensitive to the presence of a background plasma owing to its coupling to electromagnetism. Such a scenario is particularly relevant for superradiant axion condensate around stellar mass black holes since the axion mass can be within a few orders of magnitude of the plasma frequency of the surrounding medium. In this paper I discuss the properties of the plasma around a black hole and analyze its effects on the lasing of a uniform axion condensate of mass of the order of the plasma frequency.
Detecting ultralight axions from multifrequency observations of neutral hydrogen intensity mapping
本研究探讨了超轻轴子对再电离后中性氢信号的影响，揭示了其在不同质量范围内的暗物质或暗能量特性，并利用未来强度映射巡天的角相关函数探索了暗能量、中微子与ULAs之间的参数空间及简并性。
Enhancing Constraints on Ultralight Axion Dark Matter from Gravitational Capture
该研究利用太阳引力捕获超轻轴子产生的玻色增强效应，显著放大局部暗物质密度，并据此更新轴子-光子耦合的实验限制与未来预测。
We present a brief overview of a new generation of high-precision laboratory and astrophysical measurements to search for ultralight (sub-eV) axion, axion-like pseudoscalar and scalar dark matter, which form either a coherent condensate or topological defects (solitons). In these new detection methods, the sought effects are linear in the interaction constant between dark matter and ordinary matter, which is in stark contrast to traditional searches for dark matter, where the sought effects are quadratic or higher order in the underlying interaction constants (which are extremely small).
Constraints on axion-like ultralight dark matter from observations of the HL Tauri protoplanetary disk
本文利用HL Tauri原行星盘的极化观测未发现极化角变化，约束了类轴子超轻暗物质的质量与光子耦合。
Dynamical dark energy from an ultralight axion
针对DES观测到的暗能量状态方程偏离宇宙学常数，提出超轻轴子模型，其质量约2×10^-33 eV，可解释w≥-1且偏好负宇宙学常数，并给出简化公式便于拟合。
If a global chiral symmetry is explicitly broken by anomalies in nonabelian gauge theories, a pseudo Nambu-Goldstone boson (axion) associated with a spontaneous breakdown of such a global symmetry acquires a mass through nonperturbative instanton effects. We calculate the axion mass assuming a supersymmetric SU(2) gauge theory and show that the axion obtains an extremely small mass when the SU(2) gauge symmetry is broken down at very high energy, say at the Planck scale. We identify the axion with a hypothetical ultralight boson field proposed to account for a small but nonzero cosmological co…
The self-attractive ultralight axion and its time scale of collapsing in general relativistic framework
本文在广义相对论框架下利用自吸引超轻轴子暗物质的坍缩临界条件，估算高红移超大质量黑洞形成的时间与长度尺度，为其及JWST所见小红点的轴子起源提供理论支持。
Axion particles can form macroscopic condensates, whose size can be galactic in scale for models with very small axion masses $m\sim10^{-22}$ eV, and which are sometimes referred to under the name of Fuzzy Dark Matter. Many analyses of these condensates are done in the non-interacting limit, due to the weakness of the self-interaction coupling of axions. We investigate here how certain results change upon inclusion of these interactions, finding a decreased maximum mass and a modified mass-radius relationship. Further, these condensates are, in general, unstable to decay through number-changin…
We present a complete halo model for mixed dark matter composed of cold dark matter (CDM) and ultralight axion-like particles (ULAs). Our model treats ULAs as a biased tracer of CDM, in analogy to treatments of massive neutrinos and neutral hydrogen. The model accounts for clustering of ULAs around CDM host halos, and fully models the cross correlations of both components. The model inputs include the ULA Jeans scale, and soliton density profile. Our model can be used to predict the matter power spectrum, $P(k)$, on non-linear scales for sub-populations of ULAs across the mass range $10^{-33}\…
Implication of nano-Hertz stochastic gravitational wave background on ultralight axion particles
针对脉冲星计时阵列观测到的随机引力波背景，研究通过分析克尔黑洞与超辐射轴子云构成的引力原子能级跃迁，结合贝叶斯分析支持约10⁻²¹eV超轻轴子解释，其质量与模糊暗物质典型值一致。
A Ramsey Neutron-Beam Experiment to Search for Ultralight Axion Dark Matter at the ESS
本研究提出在欧洲散裂源HIBEAM束线开展新型Ramsey中子束实验，利用轴子与中子自旋的耦合搜寻超轻轴子暗物质，预计可将相关耦合的探测灵敏度较现有水平提升2-3个数量级。
A Fast and Accurate Implementation of the Effective Fluid Approximation for Ultralight Axions
在CAMB中实现了超轻轴子的有效流体近似，达到亚百分比精度，并通过MCMC分析改进了对轴子质量和丰度的约束。
Ultralight axion-like particles are well-motivated dark matter candidates that are the target of numerous direct detection efforts. In the vicinity of the Solar System, such particles can be treated as oscillating scalar fields. The velocity dispersion of the Milky Way determines a coherence time of about 10^6 oscillations, beyond which the amplitude of the axion field fluctuates stochastically. Any analysis of data from an axion direct detection experiment must carefully account for this stochastic behavior to properly interpret the results. This is especially true for experiments sensitive t…
Ultralight scalar and axion dark matter detection with atom interferometers
本文提出利用原子干涉仪探测超轻标量和轴子暗物质，通过计算差分相移给出耦合参数约束，有望提升探测灵敏度并与其他实验互补。
An ultralight scalar boson with mass $m_1 \simeq 10^{-22}$ eV is gaining credence as a Dark Matter (DM) candidate that explains the dark cores of dwarf galaxies as soliton waves. Such a boson is naturally interpreted as an axion generic in String Theory, with multiple light axions predicted in this context. We examine the possibility of soliton structures over a wide range of scales, accounting for galaxy core masses and the common presence of nuclear star clusters. We present a diagnostic soliton core mass-radius plot that provides a global view, indicating the existence of an additional axio…
Searches for ultralight vector and axion dark matter with KAGRA
本研究提出用激光干涉引力波探测器搜寻超轻矢量与轴子暗物质，综述了日本KAGRA探测器的相关进展，含2020年首次矢量暗物质搜寻及2025年观测运行的轴子搜寻偏振光学装置安装计划。
Gravitational lensing time delays offer an avenue to measure the Hubble parameter $H_0$, with some analyses suggesting a tension with early-type probes of $H_0$. The lensing measurements must mitigate systematic uncertainties due to the mass modelling of lens galaxies. In particular, a core component in the lens density profile would form an approximate local mass sheet degeneracy and could bias $H_0$ in the right direction to solve the lensing tension. We consider ultralight dark matter as a possible mechanism to generate such galactic cores. We show that cores of roughly the required propert…
Ultralight axions (ULAs) are promising dark matter candidates that can have a distinct impact on the formation and evolution of structure on nonlinear scales relative to the cold, collisionless dark matter (CDM) paradigm. However, most studies of structure formation in ULA models do not include the effects of self-interactions, which are expected to arise generically. Here, we study how the tidal evolution of solitons is affected by ULA self-interaction strength and sign. Specifically, using the pseudospectral solver UltraDark.jl, we simulate the tidal disruption of self-interacting solitonic …
Search for Ultralight Axion Dark Matter with a Levitated Ferromagnetic Torsional Oscillator
利用悬浮铁磁扭转振荡器探测超轻轴子暗物质，通过高真空和磁屏蔽获得18000秒数据，设定90%置信度限，未来计划通过优化提升灵敏度。
We revisit the limit on very light axion-like particles (ALPs) from the absence of gamma rays coincidental with the neutrino burst from SN1987A. We use updated supernova simulations, modern models for the magnetic field inside the Galaxy, and a Primakoff cross section which takes into account proton-degeneracy and mass-reduction effects. We finally give an updated exclusion plot for the electromagnetic coupling of sub-eV ALPs, comparing our new bound with other limits as well as with future ALP searches.
Scenarios with axion-like particles of variable masses, from the milli-eV range to ultralight, can be generated in a natural way in the context of effective field theory models with anomalous $U(1)$ gauge symmetries. They include dimension-5 operators which define a coupling of the axion to the gauge anomaly. They provide a realization, in the domain of ordinary gauge theories, of models for such particles, which evade the usual mass/coupling constraint of ordinary (Peccei-Quinn) axions and are natural dark matter candidates. As an illustration of these models, we present an overview of two of…
The highly populated, low-energy excitations of a scalar field of mass $m_a\sim 10^{-22}\,\textrm{eV}$ can represent the full dark matter content of the universe and alleviate some tensions in the standard cosmological scenario on small-scales. This {\it fuzzy dark matter} component is commonly assumed to arise as the consequence of a new axion-like particle in the matter sector, yet for simplicity it is usually modeled in terms of a simple free quadratic field. In this paper we consider how the cosmological constraints are modified when the effects of an instanton potential and temperature-de…
The SRG/eROSITA all-sky survey: Constraints on Ultra-light Axion Dark Matter through Galaxy Cluster Number Counts
利用SRG/eROSITA首次全天空调查与弱引力透镜数据，研究超轻轴子在暗物质中的占比，发现新的约束结果。
Axion-like fields are naturally generated by a mechanism of anomaly cancellation of one or more anomalous gauge abelian symmetries at the Planck scale, emerging as duals of a two-form from the massless bosonic sector of string theory. This suggests an analogy of the Green-Schwarz mechanism of anomaly cancellation, at field theory level, which results in one or more Stueckelberg pseudoscalars. In the case of a single Stueckelberg pseudoscalar $b$, vacuum misalignments at phase transitions in the early Universe at the GUT scale provide a small mass - due to instanton suppression of the periodic …
Lecture Notes: Probing ultralight axion-like particles with quantum technology
本文综述了利用量子技术探测超轻轴子状粒子作为暗物质候选者的物理原理和实验方法，涵盖轴子-光子耦合驱动的转换搜索及高精度实验，如原子钟、光学谐振腔等，强调不同技术的互补性与发现潜力。
We argue that a new type of extremely light axion is generically present in the type IIB part of the string theory landscape. Its mass is suppressed by the third power of the warp factor of a strongly warped region (Klebanov-Strassler throat), suggesting the name thraxion. Our observation is based on the generic presence of several throats sharing the same 2-cycle. This cycle shrinks to zero volume at the end of each throat. It is hence trivial in homology and the corresponding $C_2$ axion is massive. However, the mass is warping-suppressed since, if one were to cut off the strongly warped reg…
Muonium Spectroscopy as a Quantum Sensor for Ultralight Axion Dark Matter
本研究提出一种基于缪onium的轴子搜索新方法，利用高强度缪子束的共振量子跃迁（MASH），可在18-130μeV轴子质量范围内收紧轴子-缪子耦合约束，拓展暗物质探测通道。
Neutrino Lorentz invariance violation and ultralight axion-like dark matter searches at the European Spallation Source
针对暗物质探测难题，研究中微子与超轻类轴子（UALP）的相互作用及其引发的洛伦兹与$CPT$对称性破缺，评估欧洲散裂中子源（ESS）下一代中微子振荡实验对相关SME系数与有效耦合的探测灵敏度。
It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with $m_a\sim 10^{-22}\text{eV}$ are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here we use realistic kinematic mock data catalogs of Milky Way dSph's to show that the "mass-anisotropy degeneracy" in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown…
Ultralight-axion (ULA) dark matter is one of the possible solutions to resolve small-scale problems, especially the core-cusp problem. This is because ULA dark matter can create a central soliton core in all dark matter haloes stemmed from the quantum pressure against gravity below the de Broglie wavelength, which becomes manifest on astrophysical scales with axion mass range $\sim10^{-22}$ eV. In this work, we apply our non-spherical dynamical models to the kinematic data of eight classical dwarf spheroidals (dSphs) to obtain more reliable and realistic limits on ULA particle mass. This is mo…
Probing an ultralight QCD axion with electromagnetic quadratic interaction
本研究针对超轻QCD轴子，探究了由圈图阈值修正产生的电磁二次耦合，指出其可通过光学原子钟等新途径探测轴子，还推导了暗物质速度弥散引发的低频涨落背景的功率谱解析表达式，为更重轴子的搜寻提供了新方法与实验思路。
Inflationary Axion Isocurvature in the CMB across All Ultralight Masses
该研究扩展AxiECAMB的ETA方法，分析全超轻质量范围轴子等曲率扰动，给出解析公式与约束，指出特定质量区域的信号特征及共存窗口，或缓解S8张力。
Ultralight axion or axion-like particle dark matter and 21-cm absorption signals in new physics
本文研究超轻轴子暗物质通过重子冷却和光子加热解释21厘米吸收信号，并发现加热效应消除了冷却产生的多余中微子种类数。
Accurate method for ultralight axion CMB and matter power spectra
研究超轻轴子宇宙微波背景和物质功率谱的精确方法，在全宇宙学玻尔兹曼代码中实现技术扩展，覆盖\(10^{-33} \lesssim m/{\rm eV} \lesssim 10^{-18}\)范围，提升功率谱精度，或影响解决\(\Lambda\)CDM中张力的模型参数。
Measuring Ultralight-Axion Coherence with Galaxy Polarization Correlations
研究利用星系偏振旋转角的三维两点相关性测量超轻类轴子双折射场幅度及相干尺度，通过检测星系对相关性转折测特征动量尺度，幅度约束相关参数，对特定基准调查给出灵敏度等结果，提供了一种晚期探测方法。
We examine whether the Hubble tension, the mismatch between early and late measurements of $H_0$, can be alleviated by ultralight scalar fields in the early universe, and we assess its plausibility within UV physics. Since their energy density needs to rapidly redshift away, we explore decays to massless fields around the era of matter-radiation equality. We highlight a concrete implementation of ultralight pseudo-scalars, axions, that decay to an abelian dark sector. This scenario circumvents major problems of other popular realizations of early universe scalar models in that it uses a regula…
Search for ultralight dark matter in the SuperMAG high-fidelity dataset
本研究在SuperMAG高保真数据集中搜寻超轻暗物质振荡磁场信号，填补了参数空间空白，未发现候选者，并设定了该质量范围内的领先直接约束。
New Limits on Ultralight Axionlike Dark Matter from Reanalyzed Data
本文重新分析 Lorentz/CPT 破缺实验数据，在超轻类轴子质量区间给出轴子–核子耦合新限制，部分结果改进逾3个数量级并超越 SN1987A 天体物理限制。
The $π$-axion and $π$-axiverse of dark QCD
本研究提出暗QCD框架下的π-轴子宇宙理论，预言N_f²-1种超轻类轴子粒子，通过暗光子与可见光子的动力学耦合构建可见区门户，可在多种实验中检验，是弦理论轴子宇宙的补充。
Ultralight dark matter detection with levitated ferromagnets
本研究探讨了悬浮铁磁体对交流磁场的响应，并预测其对超轻暗物质（如类轴子和暗光子）的探测灵敏度，发现现有装置灵敏度可媲美传统实验，未来有望成为探测多种暗物质耦合的灵敏探针。
In this work, we study the propagation of high energy neutrinos produced in extragalactic sources including the effect of a possible interaction with ultralight axion-like particles (UALP) with a mass $m_a\sim 10^{-22} {\rm eV}$ as the constituents of dark matter (DM) under the assumption that their coupling to neutrinos is dominant. We compute the cross section and describe the propagation of a diffuse neutrino flux using transport equations for each mass eigenstate. This allows us to obtain the neutrino fluxes of the different flavors to be observed at the Earth with neutrino telescopes unde…
Double the axions, half the tension: multi-field early dark energy eases the Hubble tension
多场早期暗能量模型缓解了Planck数据对轴子早期暗能量的严格约束，2-field模型中哈勃常数残余张力为1.5σ，且最佳拟合值比单场模型大1.4σ。
Collective response and noise of a levitated ferromagnet lattice for ultralight dark matter detection
本文研究了悬浮铁磁体晶格作为超轻暗物质探测器的可行性，通过理论分析集体响应和噪声预算，展示了晶格在提高探测灵敏度和增强信号方面优于单个铁磁体的优势。
Probing Extragalactic Ultralight Axion Dark Matter with Decade-long Blazar Optical Polarimetry of 1ES 1959+650
本文利用耀变体1ES 1959+650的十年光学偏振数据首次搜索类轴子暗物质诱导的偏振角周期振荡，未发现显著信号，并在广泛质量范围内对ALP-光子耦合常数给出严格上限，证明长期耀变体偏振测量是探测河外类轴子暗物质的有效互补手段。
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