用DES-Y1和外部数据对宇宙晚期暗物质到暗辐射转换的约束
Constraints on dark matter to dark radiation conversion in the late universe with DES-Y1 and external data
摘要：
我们研究了一类在低红移时期暗物质转变为暗辐射的唯象模型。这类被称为DMDR的模型，用两个额外的参数来描述共同运动的暗物质密度的演化，并且可能有助于减轻早期和晚期宇宙探测之间观察到的差异。我们调查如何转换影响关键的宇宙学观测，如CMB温度和物质的功率谱。结合来自暗能量调查第一年的3x 2 pt数据，{ \it Planck}-2018 CMB温度和偏振数据，来自Pantheon的超新星（SN）Ia型数据，以及来自BOSS DR 12，MGS和6dFGS的重子声振荡（BAO）数据，我们对已转换为暗辐射的暗物质的数量以及这种转换的速率提出了新的限制。以当前暗物质量$ζ$为单位，自宇宙开始以来已经转换的暗物质的分数被限制在68\%的置信水平下，对于DES-Y1 3x 2 pt数据为$<0.32$，对于CMB+SN+BAO数据为$<0.030$，对于组合数据集为$<0.037$。DES和CMB+SN+BAO数据集一致的概率从$Λ$ CDM模型的4%增加到DMDR的8%（张力较小）。DES-Y1 3x 2 pt和CMB+SN+BAO之间的$S_8 = σ_8 \sqrt{Ω_{\rm m}/0.3}$张力从$2.3σ$略微降低至$1.9σ$。我们发现没有减少哈勃紧张时，合并的数据相比，在DMDR模型中的距离阶梯测量。DMDR和$Λ$ CDM模型的最大后验拟合优度统计是可比的，表明DMDR宇宙学没有$Λ$ CDM的偏好。
英文摘要：
We study a phenomenological class of models where dark matter converts to dark radiation in the low redshift epoch. This class of models, dubbed DMDR, characterizes the evolution of comoving dark matter density with two extra parameters, and may be able to help alleviate the observed discrepancies between early- and late-time probes of the universe. We investigate how the conversion affects key cosmological observables such as the CMB temperature and matter power spectra. Combining 3x2pt data from Year 1 of the Dark Energy Survey, {\it Planck}-2018 CMB temperature and polarization data, supernovae (SN) Type Ia data from Pantheon, and baryon acoustic oscillation (BAO) data from BOSS DR12, MGS and 6dFGS, we place new constraints on the amount of dark matter that has converted to dark radiation and the rate of this conversion. The fraction of the dark matter that has converted since the beginning of the universe in units of the current amount of dark matter, $ζ$, is constrained at 68\% confidence level to be $<0.32$ for DES-Y1 3x2pt data, $<0.030$ for CMB+SN+BAO data, and $<0.037$ for the combined dataset. The probability that the DES and CMB+SN+BAO datasets are concordant increases from 4\% for the $Λ$CDM model to 8\% (less tension) for DMDR. The tension in $S_8 = σ_8 \sqrt{Ω_{\rm m}/0.3}$ between DES-Y1 3x2pt and CMB+SN+BAO is slightly reduced from $2.3σ$ to $1.9σ$. We find no reduction in the Hubble tension when the combined data is compared to distance-ladder measurements in the DMDR model. The maximum-posterior goodness-of-fit statistics of DMDR and $Λ$CDM model are comparable, indicating no preference for the DMDR cosmology over $Λ$CDM.
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