Liang Chen, Thomas W. Kephart
We model clusters of axions with spherically symmetric spacial but arbitrary momentum distributions and study the directional profile of photos produced in their evolution through spontaneous and stimulated decay of axions via the process a --> gamma + gamma. Several specific examples are presented.
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We model clusters of axions with spherically symmetric momentum but arbitrary spatial distributions and study the directional profile of photos produced in their evolution through spontaneous and stimulated decay of axions via the process $a \rightarrow γ+ γ$. Several specific examples are presented.
We discuss a possible principle for detecting dark matter axions in galactic halos. If axions constitute a condensate in the Milky Way, stimulated emissions of the axions from a type of excitation in condensed matter can be detectable. We provide general mechanism for the dark matter emission, and, as a concrete example, an emission of dark matter axions from magnetic vortex strings in a type II superconductor are investigated along with possible experimental signatures.
If their number density is high enough, clusters of axions can decay to photons via stimulated emission. We study both the special and general relativistic corrections to lasing in such dense axion clusters as they evolve in static spacetimes. Our main results are rate equations for the evolution of axion and photon number densities that include these corrections. We use Schwarzschild spacetime as a detailed example.
Effects of stimulated emission and superradiant growth of non-spherical axion cluster
本文研究了非球形轴子团簇中光子的受激辐射，发现无黑洞超辐射源时产生单脉冲，有源时产生多脉冲并使团簇趋于球对称，为快速射电暴提供了候选解释。
Remote sensing of backward reflection from stimulated axion decay
本研究提出利用相干光子场中冷暗物质诱导衰变的后向反射遥感探测方法，结合地球引力透镜效应，给出受激反射公式与本地、远程实验灵敏度，可探测eV能标轴子的光子耦合至对应量级。
We propose a three-beam stimulated resonant photon collider with focused laser fields in order to directly produce an axion-like particle (ALP) with the two beams and to stimulate its decay by the remaining one. The expected sensitivity around the eV mass range has been evaluated. The result shows that the sensitivity can reach the ALP-photon coupling down to $\mathcal{O}(10^{-14})$ GeV${}^{-1}$ with 1 J class short-pulsed lasers.
Detection of dilute axion stars with stimulated decay
针对第九行星可能为稀释轴子星的假说，提出用50MW无线电波束诱发受激发射衰变，并通过地面射电望远镜探测回波以区分其他候选体。
Detecting the Stimulated Decay of Axions at Radio Frequencies
假设类轴子粒子构成全部暗物质，研究其在射电频率衰变为光子的探测可能性，发现环境辐射场可通过受激发射将信号放大数个数量级，并指出下一代射电望远镜如平方千米阵有望探测到该信号。
Dark matter axion condensates may experience stimulated decays into photon pairs. This effect has been often interpreted as a parametric resonance of photons from the axion-photon coupling, leading to an exponential growth of the photon occupation number in a narrow instability band. Most of the previous literature does not consider the possible evolution of the axion field due to the photon growth. We revisit this effect presenting a mean field solution of the axion-photon kinetic equations, in terms of number of photons and pair correlations. We study the limit of no axion depletion, recover…
The superradiant instability can lead to the generation of extremely dense axion clouds around rotating black holes. We show that, despite the long lifetime of the QCD axion with respect to spontaneous decay into photon pairs, stimulated decay becomes significant above a minimum axion density and leads to extremely bright lasers. The lasing threshold can be attained for axion masses $μ\gtrsim 10^{-8}\ \mathrm{eV}$, which implies superradiant instabilities around spinning primordial black holes with mass $\lesssim 0.01M_\odot$. Although the latter are expected to be non-rotating at formation, a…
Enhanced extragalactic photon flux by PBH in a stimulated axion/ALP decay scenario
本研究提出黑洞超辐射下轴子/类轴子的受激衰变可用于搜寻原初黑洞，推导了对应粒子与黑洞质量区间下原初黑洞的占比上限，为相关天体物理观测提供约束依据。
Stimulated decay of collapsing axion stars and fast radio bursts
本研究提出坍缩轴子星可通过受激衰变产生射电暴，解释快速射电暴的辐射机制，并预测FAST或SKA可观测到相应信号。
Coherent versus incoherent amplification: from parametric resonance to the kinetic regime in stimulated axion decay
本文研究受激轴子衰变中相干与不相干放大的差异，揭示参数共振（$s\propto g_{a\gamma}$）与动力学行为（$s\propto g_{a\gamma}^2$）源于轴子场的相干性，并推导出统一的有效演化方程及交叉描述。
Opening a meV mass window for Axion-like particles with a microwave-laser-mixed stimulated resonant photon collider
本文提出微波-激光混合三束受激共振光子对撞机，可在meV质量范围探测类轴子粒子，结合高强度激光与速调管后灵敏度可达O(10^{-13}) GeV^{-1}，为独立验证ALPs暗物质本质开辟新途径。
On the Galactic radio signal from stimulated decay of axion dark matter
本研究分析银河系轴子暗物质受激衰变的射电辐射全天分布，结合观测确定激发辐射分布，对比超新星遗迹并考虑吸收效应，得出不同暗物质轮廓下的信号强弱分布，验证了平方公里阵列对特定参数轴子的探测潜力。
Stimulated capture of axion dark matter around primordial black holes
该研究探讨原初黑洞周围轴子暗物质的受激捕获，推导类氢基态云形成与存活的判据，分析其在中子星磁层共振转换及微引力透镜畸变方面的观测意义。
Detecting dilute axion stars constrained by fast radio bursts in the Solar System via stimulated decay
本研究提出向太阳系内可能存在的、受快速射电暴约束的稀薄轴子星发射强无线电波束，通过探测受激衰变回波检验其存在，为暗物质本质、FRB起源及哈勃张力问题提供研究途径。
Looking in the axion mirror: An all-sky analysis of stimulated decay
本研究分析轴子暗物质受激衰变产生的全天回波图像，利用多类天体作为激发辐射源构建信号模板，预测多款现有射电望远镜可无需新增硬件，在执行原有任务的同时开展有竞争力的轴子探测实验。
Listening for echo from the stimulated axion decay with the 21 CentiMeter Array
本研究提出利用21 CentiMeter Array在0.41至1.6μeV质量范围内搜寻受激轴子暗物质衰变的回波信号，通过1MW发射机覆盖其频率范围，使轴子-光子耦合灵敏度较现有极限提升约一个数量级。
A prominent aspect of the hunt for cold dark matter is looking for light scalar candidates such as axion-like particles (ALPs). The coupling between ALPs and photons allows for the spontaneous decay of ALPs into pairs of photons. It has been previously shown that stimulated ALP decay rates can become significant on cosmic time scales. Furthermore, it has been claimed, in several recent works, that ALPs can gravitationally thermalize and form macroscopic condensates. Consequently, the photon occupation number of ambient populations (like the cosmic microwave background) can receive Bose enhance…
Self-stimulated avalanche in superradiant axion clouds
研究旋转黑洞周围的玻色子云通过超辐射形成引力原子，并发生自激雪崩式相干四极跃迁，产生具有特征包络的延迟引力波脉冲，提出一种探测超轻暗物质的新方法。
We develop a formalism to describe extensions of existing axion haloscope designs to those that possess directional sensitivity to incoming dark matter axion velocities. The effects are measurable if experiments are designed to have dimensions that approach the typical coherence length for the local axion field. With directional sensitivity, axion detection experiments would have a greatly enhanced potential to probe the local dark matter velocity distribution. We develop our formalism generally, but apply it to specific experimental designs, namely resonant cavities and dielectric disk halosc…
We have searched for axion-like resonance states by colliding optical photons in a focused laser field (creation beam) by adding another laser field (inducing beam) for stimulation of the resonance decays, where frequency-converted signal photons can be created as a result of stimulated photon-photon scattering via exchanges of axion-like resonances. A quasi-parallel collision system (QPS) in such a focused field allows access to the sub-eV mass range of resonance particles. In past searches in QPS, for simplicity, we interpreted the scattering rate based on an analytically calculable symmetri…
We study the directional effect of the expected axion dark matter signal in a resonant cavity of an axion haloscope detector, for cavity geometries not satisfying the condition that the axion de Broglie wavelength $λ_a$ is sufficiently larger than the cavity dimensions $L$ for a fully coherent conversion, i.e. $λ_a \gtrsim 2πL$. We focus on long thin cavities immersed in dipole magnets and find, for appropriately chosen cavity lengths, an O(1) modulation of the signal with the cavity orientation with respect the momentum distribution of the relic axion background predicted by the isothermal sp…
Single-Point Search for eV-scale Axion-like particles with Variable-Angle Three-Beam Stimulated Resonant Photon Collider
该研究利用可变角度三束激发共振光子对撞机，在eV量级范围内首次对轴子类粒子进行无模型依赖的耦合系数上限测量。
We study the propagation of photons in a homogeneous axion dark matter background. When the axion decay into two photons is stimulated, the photon field exhibits a parametric instability in a small bandwidth centered on one half of the axion mass. We estimate analytically the enhancement for both coherent and non-coherent axion fields and we find that this effect could be relevant in the context of miniclusters and galactic halos.
A Review of Axion Lasing in Astrophysics
本文综述了天体物理环境中轴子受激衰变为光子并形成激射或微波激射的条件、可能出现的情境及其探测前景。
Anatomy of astrophysical echoes from axion dark matter
本研究从第一性原理推导μeV类轴子粒子受银河射电源辐射诱导发生受激衰变所产生的两个回声与共线发射信号，并以脉冲星为例给出未来观测预测。
Earth-lens telescope for distant axion-like particle sources with stimulated backward reflection
提出基于地球引力透镜与受激后向反射的望远镜概念，数值分析焦点结构并开发估算框架，在eV质量范围内对ALP-光子耦合的探测灵敏度达$\mathcal{O}(10^{-22})\mathrm{GeV}^{-1}$，为天基ALP观测台开辟新路径。
The nature of dark matter is one of the longest-standing puzzles in science. Axions or axion-like particles are a key possibility, and arise in mechanisms to solve the strong CP problem but also in low-energy limits of string theory. Extensive experimental and observational efforts are actively looking for `axionic' imprints. Independently on their nature, their abundance, and on their contribution to the dark matter problem, axions form dense clouds around spinning black holes, grown by superradiant mechanisms. It was recently suggested that once couplings to photons are considered, an expone…
Radio Killed the Axion Star: Constraining Axion Properties with Radio Telescopes
本文提出轴子暗物质在暗物质晕中心形成的轴子星坍缩爆炸产生“轴子新星”，并在轴子-光子耦合适度增强的模型下释放显著射电光子，进而确定了可通过射电暂现源搜索探测轴子新星的参数范围。
Within the dual symmetric point of view, the theory for seeking axion dark matter via haloscope experiments is derived by exactly solving the dual symmetric axion electrodynamics equation. Notwithstanding that the conventional theory of axion electrodynamics presented in [Phys. Rev. Lett. 51, 1415 (1983) and J. Phys. A: Math. Gen. 19, L33 (1986)] is more commonly used in haloscope theory, we show that the dual symmetric axion electrodynamics has more advantages to apply to haloscope theory. First, the dual symmetric and conventional perspectives of axion electrodynamics coincide under long-wav…
Dark matter consisting of very light and very weakly interacting particles such as axions, axion-like particles and hidden photons could be detected using reflective surfaces. On such reflectors some of the dark matter particles are converted into photons and, given a suitable geometry, concentrated on the detector. This technique offers sensitivity to the direction of the velocity of the dark matter particles. In this note we investigate how far spherical mirrors can concentrate the generated photons and what this implies for the resolution in directional detection as well as the sensitivity …
It was recently shown that a powerful beam of radio/microwave radiation sent out to space can produce detectable back-scattering via the stimulated decay of ambient axion dark matter. This echo is a faint and narrow signal centered at an angular frequency close to half the axion mass. In this article, we provide a detailed analytical and numerical analysis of this signal, considering the effects of the axion velocity distribution as well as the outgoing beam shape. In agreement with the original proposal, we find that the divergence of the outgoing beam does not affect the echo signal, which i…
A Photon Cloud Induced from an Axion Cloud
研究了由轴子云在 Kerr 黑洞附近诱导的光子云，揭示了其在轴子场超辐射条件下指数增长的特性及对观测的潜在贡献。
Light axions ($m_a \lesssim 10^{-10}$ eV) can form dense clouds around rapidly rotating astrophysical black holes via a mechanism known as rotational superradiance. The coupling between axions and photons induces a parametric resonance, arising from the stimulated decay of the axion cloud, which can rapidly convert regions of large axion number densities into an enormous flux of low-energy photons. In this work we consider the phenomenological implications of a superradiant axion cloud undergoing resonant decay. We show that the low energy photons produced from such events will be absorbed ove…
Axions are a theoretically promising dark matter (DM) candidate. In the presence of radiation from bright astrophysical sources at radio frequencies, nonrelativistic DM axions can undergo stimulated decay to two nearly back-to-back photons, meaning that bright sources of radio waves will have a counterimage ("gegenschein") in nearly the exact opposite spatial direction. The counterimage will be spectrally distinct from backgrounds, taking the form of a narrow radio line centered at $ν= m_a/4π$ with a width determined by Doppler broadening in the DM halo, $Δν/ν\sim 10^{-3}$. In this work, we sh…
We study parametric instability of compact axion dark matter structures decaying to radiophotons. Corresponding objects - Bose (axion) stars, their clusters, and clouds of diffuse axions - form abundantly in the postinflationary Peccei-Quinn scenario. We develop general description of parametric resonance incorporating finite-volume effects, backreaction, axion velocities and their (in)coherence. With additional coarse-graining, our formalism reproduces kinetic equation for virialized axions interacting with photons. We derive conditions for the parametric instability in each of the above obje…
We investigate a novel technique for the astrophysical detection of axions or axion-like particles in the dark matter halo of the Milky Way based on stimulated decay of axions, which we call axion gegenschein emission. Photons from the brightest known radio sources with a frequency equal to half the axion mass stimulate axion decay while propagating through the dark matter halo, causing radio emission in a direction precisely opposite to the incoming photon in the axion rest-frame and creating a countersource for every radio source, with an image smoothed by the dark matter velocity dispersion…
Hidden photon and axion-like dark matter may be detected using spherical reflective surfaces such as dish antenna setups converting some of the dark matter particles into photons and concentrating them on a detector. These setups may be used to perform directional searches measuring the dark matter momentum distribution. We briefly review the photon distribution one expects to detect with such an antenna and directional resolution in ray approximation. Furthermore we consider the regime $m_{DM} \lesssim (R_{sp}\,v_{DM})^{-1}$ where this approximation does not hold anymore due to the photon wav…
We study the effect of the axion dark matter velocity in the recently proposed dielectric haloscopes, a promising avenue to search for well-motivated high mass ($40-400~μ$eV) axions. We describe non-zero velocity effects for axion-photon mixing in a magnetic field and for the phenomenon of photon emission from interfaces between different dielectric media. As velocity effects are only important when the haloscope is larger than about 20% of the axion de Broglie wavelength, for the planned MADMAX experiment with 80 dielectric disks the velocity dependence can safely be neglected. However, an au…
Stimulated decays of axion dark matter, triggered by a source in the sky, could produce a photon flux along the continuation of the line of sight, pointing backward to the source. The strength of this so-called axion "echo" signal depends on the entire history of the source and could still be strong from sources that are dim today but had a large flux density in the past, such as supernova remnants (SNRs). This echo signal turns out to be most observable in the radio band. We study the sensitivity of radio telescopes such as the Square Kilometer Array (SKA) to echo signals generated by SNRs th…
Axion dark matter can resonantly convert to photons in the magnetosphere of neutron stars, possibly giving rise to radio signals observable on Earth. This method for the indirect detection of axion dark matter has recently received significant attention in the literature. The calculation of the radio signal is complicated by a number of effects; most importantly, the gravitational infall of the axions onto the neutron star accelerates them to semi-relativistic speed, and the neutron star magnetosphere is highly anisotropic. Both of these factors complicate the calculation of the conversion of …
It is an intriguing possibility that the cold dark matter of the Universe may consist of very light and very weakly interacting particles such as axion(-like particles) and hidden photons. This opens up (but also requires) new techniques for direct detection. One possibility is to use reflecting surfaces to facilitate the conversion of dark matter into photons, which can be concentrated in a detector with a suitable geometry. In this note we show that this technique also allows for directional detection and inference of the full vectorial velocity spectrum of the dark matter particles. We also…
Axions are a promising dark matter candidate that were motivated to solve the strong CP problem and that may also address the cosmological matter-antimatter asymmetry. Axion-photon conversion is possible in the presence of the strong magnetic fields, and the photon so produced will have energy equal to the axion mass. Here we report new limits on axionic dark matter obtained from radio spectra of the Galactic Center magnetar PSR J1745-2900. The magnetar has a magnetic field of $1.6\times10^{14}$ G that interacts with a dark matter density $2\times10^5$ to $2\times10^9$ times greater than the l…
In the past few years, the search for axion-like particles (ALPs) has grown significantly due to their potential to account for the total abundance of the cold dark matter (CDM) in the universe. The coupling between ALPs and photons allows the spontaneous decay of ALPs into pairs of photons. For ALPs condensed in CDM halos around galaxies, the stimulated decay of ALPs is also possible. In this work, we examine the detectability of the radio emissions produced from this process with forthcoming radio telescopes such as the Square Kilometer Array (SKA) and MeerKAT. Our results, using recent more…
Probing axion-like particles at the Electron-Ion Collider
本文评估EIC通过相干散射中光子融合产生并双光子衰变的ALPs，结合即时衰变与偏移顶点搜索，可覆盖0.2–20 GeV质量区间内大量未探索参数空间。
Invisible Neutrino Decays as Origin of TeV Gamma Rays from GRB221009A
针对 GRB221009A 的高能伽马射线，本文提出中微子衰变为类轴子粒子并在银河磁场中转化为伽马射线的机制，以缓解耦合与质量约束矛盾。
Dark Matter Detection through Rydberg Atom Transducer
本文提出一种整合介电卤素、里德堡原子转换器和超导纳米线单光子探测器的混合检测架构，利用里德堡原子六波混频将THz信号转换到光学领域，实现对轴子-光子耦合常数的高灵敏度探测。
We propose a simple mechanism of light dark matter (DM) production from the decay of the oscillating inflaton condensation. If the reheating temperature after inflation is higher than the inflaton mass, which is of the same order of the momentum of the DM at the time of the production, the DM momentum can be suppressed compared to the temperature of the thermal plasma if the interaction of the DM is weak enough. Consequently, the DM can be cold enough to avoid the observational constraints on the warm DM, like the Lyman-$α$ bound even if the DM mass is small. We study the bosonic and fermionic…
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