If a fraction of the dark matter is unstable and decays into dark radiation at around the time of matter-radiation equality, it could impact the expansion history of the universe in a way that helps to ameliorate the long-standing tension between the locally measured value of the Hubble constant and the value inferred from measurements of the cosmic microwave background and baryon acoustic oscillations (assuming standard $\Lambda$CDM cosmology). If this component of decaying dark matter is cold, however, it will modify the evolution of the gravitational potentials, leading to inconsistencies with these same data sets. With this in mind, we consider here a component of decaying warm dark matter, with a free-streaming length that is long enough to remain consistent with existing data. We study the background and perturbation evolution of warm decaying dark matter, and use cosmological data to constrain the mass, abundance and decay rate of such a particle. We find that a component of warm decaying dark matter can significantly reduce the tension between local and cosmological determinations of the Hubble constant.

中文翻译：

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温暖的衰变暗物质和哈勃张力

如果一部分暗物质不稳定并在物质辐射相等的时候衰变成暗辐射，它可能会影响宇宙的膨胀历史，从而有助于改善局部测量值之间长期存在的紧张关系。哈勃常数和从宇宙微波背景和重子声学振荡的测量推断的值（假设标准 $\Lambda $CDM 宇宙学）。然而，如果衰变暗物质的这一成分是冷的，它将改变引力势的演变，导致与这些相同的数据集不一致。考虑到这一点，我们在这里考虑衰变的暖暗物质的一个组成部分，其自由流动长度足够长以与现有数据保持一致。我们研究暖衰变暗物质的背景和扰动演化，并使用宇宙学数据来约束这种粒子的质量、丰度和衰变率。我们发现热衰变暗物质的一个组成部分可以显着降低哈勃常数的局部和宇宙学确定之间的张力。