Dipole radiation and beyond from axion stars in electromagnetic fields
Dipole radiation and beyond from axion stars in electromagnetic fields
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DOI：
10.1007/jhep06(2021)182
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发表时间：
2021-03
影响因子：
5.4
通讯作者：
M. Amin;A. J. Long;Zonggang Mou;P. Saffin
中科院分区：
文献类型：
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作者：
M. Amin;A. J. Long;Zonggang Mou;P. Saffin
我们研究了在外部电磁场存在的情况下，相干振荡的、空间局域的轴电离场(振荡子和轴子星)团簇产生的光子。我们用由轴子-光子耦合构成的有效无量纲耦合参数，以及轴子星的场幅、振荡频率和半径来描述光子光度的不同性质。对于小的无量纲耦合，我们给出了偶极子辐射场和每固体角的光子光度的一般解析公式，包括对组态半径的强烈依赖。对于中等到大的耦合，我们报道了在外加磁场存在的情况下光度随耦合强度的非单调行为。在初始光度随耦合强度上升之后，我们看到中等大耦合时的抑制(比偶极辐射近似大一个数量级或更多)。在足够大的耦合下，我们发现了由于参数共振而导致的发光度指数增长的转变。在小耦合和大耦合条件下，我们对轴子电动力学进行了3+1维格子模拟，包括参数共振的非微扰效应以及必要时的反反应效应。我们还讨论了导致共振轴子到光子转换的介质(等离子体)效应，孤子相干性的相关性，以及我们的结果在天体物理和宇宙学背景下的意义。
We investigate the production of photons from coherently oscillating, spatially localized clumps of axionic fields (oscillons and axion stars) in the presence of external electromagnetic fields. We delineate different qualitative behaviour of the photon luminosity in terms of an effective dimensionless coupling parameter constructed out of the axion-photon coupling, and field amplitude, oscillation frequency and radius of the axion star. For small values of this dimensionless coupling, we provide a general analytic formula for the dipole radiation field and the photon luminosity per solid angle, including a strong dependence on the radius of the configuration. For moderate to large coupling, we report on a non-monotonic behavior of the luminosity with the coupling strength in the presence of external magnetic fields. After an initial rise in luminosity with the coupling strength, we see a suppression (by an order of magnitude or more compared to the dipole radiation approximation) at moderately large coupling. At sufficiently large coupling, we find a transition to a regime of exponential growth of the luminosity due to parametric resonance. We carry out 3+ 1 dimensional lattice simulations of axion electrodynamics, at small and large coupling, including non-perturbative effects of parametric resonance as well as backreaction effects when necessary. We also discuss medium (plasma) effects that lead to resonant axion to photon conversion, relevance of the coherence of the soliton, and implications of our results in astrophysical and cosmological settings.