发表机构
Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences; School of Astronomy and Space Science, University of Science and Technology of China; Department of Strategic and Advanced Interdisciplinary Research, Peng Cheng Laboratory（中国科学院紫金山天文台暗物质与空间天文重点实验室; 中国科学技术大学天文与空间科学学院; 鹏城实验室战略与先进交叉研究部）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究测试暗物质衰变能否提高再电离光学深度，以缓解CMB与BAO测量间的差异。采用Gompertzian模型自洽计算，发现衰变暗物质仅将光学深度从0.064提升至0.072，不足以显著缓解差异，但提供了互补的寿命约束。
AI 中文摘要
DESI DR2重子声学振荡测量加剧了与宇宙微波背景（CMB）推断之间的差异，这种差异可重新表述为对再电离光学深度$\tau_{\rm reio}\simeq 0.09$的偏好，远高于从大尺度CMB偏振测量推断的$\simeq 0.06$。在此，我们测试暗物质（DM）通过$\chi\rightarrow e^{+}e^{-}$衰变产生的电磁能量注入是否能提供这一额外的光学深度。采用Gompertzian模型描述天体物理再电离，该模型提供了非对称的、经模拟校准的宇宙再电离描述，我们根据自由电子分数的演化自洽地推导出$\tau_{\rm reio}$，包括DM衰变的贡献。我们使用ACT+Planck CMB温度和偏振各向异性、CMB透镜效应、BAO测量和类星体阻尼翼观测，联合约束宇宙学、再电离参数和DM衰变率。对于$m_\chi=1\\,{\rm GeV}$，DM衰变将边缘化光学深度从$\tau_{\rm reio}=0.064$提高到$0.072$，但并未显著改善拟合。额外的光学深度主要来源于延伸至宇宙黑暗时代的宽电离尾，而非天体物理再电离的提前开始。在$m_\chi=2\\,{\rm MeV}$--$7\\,{\rm GeV}$范围内，中心68%可信区间仍低于先前发现足以将中微子质量张力和$\Lambda$CDM排除降至$2\sigma$水平以下的$\tau_{\rm reio}\simeq 0.08$水平。相应的DM寿命约束与宇宙射线和气体加热界限互补，并与之前的CMB限制相当。因此，衰变暗物质将推断的光学深度向缓解CMB--BAO差异所需的方向移动，但允许的增加仍不足以显著缓解这一差异。
英文摘要
DESI DR2 baryon acoustic oscillation measurements have sharpened a discrepancy with cosmic microwave background (CMB) inferences that can be recast as a preference for a reionization optical depth of $τ_{\rm reio}\simeq 0.09$, well above the $\simeq 0.06$ inferred from large-scale CMB polarization measurements. Here we test whether electromagnetic energy injection from dark matter (DM) decaying through $χ\rightarrow e^{+}e^{-}$ can provide this additional optical depth. Adopting a Gompertzian model for astrophysical reionization, which provides an asymmetric, simulation-calibrated description of cosmic reionization, we derive $τ_{\rm reio}$ self-consistently from the evolution of the free-electron fraction, including the contribution from DM decay. We jointly constrain cosmological and reionization parameters and the DM decay rate using ACT+Planck CMB temperature and polarization anisotropies, CMB lensing, BAO measurements, and quasar damping-wing observations. For $m_χ=1\,{\rm GeV}$, DM decay raises the marginalized optical depth from $τ_{\rm reio}=0.064$ to $0.072$, but does not significantly improve the fit. The additional optical depth arises primarily from a broad ionization tail extending through the cosmic dark ages, rather than from an earlier onset of astrophysical reionization. Across $m_χ=2\,{\rm MeV}$--$7\,{\rm GeV}$, the central $68\%$ credible intervals remain below the $τ_{\rm reio}\simeq 0.08$ level previously found sufficient to bring both the neutrino-mass tension and the exclusion of $Λ$CDM below the $2σ$ level. The corresponding DM lifetime constraints are complementary to cosmic-ray and gas-heating bounds and competitive with previous CMB limits. Decaying DM therefore shifts the inferred optical depth in the direction required to ease the CMB--BAO discrepancy, but the allowed increase remains insufficient to alleviate it substantially.
