遗迹中微子衰变对射电背景 excess 的解释
Relic neutrino decay solution to the excess radio background
AI总结：
本研究提出准简并遗迹中微子辐射衰变为惰性中微子的机制，可解释ARCADE 2探测到的射电背景 excess，给出拟合参数与约束，还预测了21厘米吸收信号并与EDGES结果对比。
摘要：
ARCADE 2探测到的射电背景 excess 是标准宇宙学模型中的一个谜题。目前没有明确可行的天体物理学解决方案，因此这可能暗示着新物理的存在。假设处于准简并态的遗迹中微子$\nu_i$（i=1、i=2或i=3均可）辐射衰变为惰性中微子$\nu_{\rm s}$，这一机制提供了一种解决方案，目前可规避不同宇宙学观测提出的所有约束，且能很好地复现ARCADE 2的数据。我们发现该机制与ARCADE 2数据拟合效果极佳，最佳拟合值为$\tau_i = 1.46 \times 10^{21}\\,{\rm s}$、$\Delta m_i = 4.0 \times 10^{-5}\\,{\rm eV}$，其中$\tau_i$为衰变寿命，$\Delta m_i$为衰变的活性中微子与惰性中微子之间的质量差。另一方面，如果遗迹中微子衰变无法解释ARCADE 2数据，那么在$1.4 \times 10^{-5} \\, {\rm eV} < \Delta m_i < 2.5 \times 10^{-4}\\,{\rm eV}$的范围内，数据会给出严格约束：$\Delta m_i^{3/2} \tau_i \gtrsim 2 \times 10^{14}\\,{\rm eV}^{3/2}\\,{\rm s}$。该解决方案还预测了比$\Lambda$CDM模型预测更强的21厘米吸收全局信号，在红移$z\simeq 17$处，对比亮温度$T_{21} = -238^{+21}_{-20}\\,{\rm mK}$（99%置信水平）。这与EDGES合作组发现的更强信号$T_{21} = - 500^{+200}_{-500}\\,{\rm mK}$存在轻微张力，表明该信号可能被高估了，或许存在某些未识别的前景源贡献。
英文摘要：
The excess radio background detected by ARCADE 2 represents a puzzle within the standard cosmological model. There is no clear viable astrophysical solution, and therefore, it might indicate the presence of new physics. Radiative decays of a relic neutrino $ν_i$ (either $i=1$, or $i=2$, or $i=3$) into a sterile neutrino $ν_{\rm s}$, assumed to be quasi-degenerate, provide a solution that currently evades all constraints posed by different cosmological observations and reproduces very well the ARCADE 2 data. We find a very good fit to the ARCADE 2 data with best fit values $τ_i = 1.46 \times 10^{21}\,{\rm s}$ and $Δm_i = 4.0 \times 10^{-5}\,{\rm eV}$, where $τ_i$ is the lifetime and $Δm_i$ is the mass difference between the decaying active neutrino and the sterile neutrino. On the other hand, if relic neutrino decays do not explain ARCADE 2 data, then these place a stringent constraint $Δm_i^{3/2} τ_i \gtrsim 2 \times 10^{14}\,{\rm eV}^{3/2}\,{\rm s}$ in the range $1.4 \times 10^{-5} \, {\rm eV} < Δm_i < 2.5 \times 10^{-4}\,{\rm eV}$. The solution also predicts a stronger 21 cm absorption global signal than the predicted one from the $Λ$CDM model, with a contrast brightness temperature $T_{21} = -238^{+21}_{-20}\,{\rm mK}$ ($99\%$ C.L.) at redshift $z\simeq 17$. This is in mild tension with the even stronger signal found by the EDGES collaboration, $T_{21} = - 500^{+200}_{-500}\,{\rm mK} $, suggesting that this might have been overestimated, possibly receiving a contribution from some unidentified foreground source.
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