Postinflationary reheating is a widely discussed mechanism for nonthermal production of dark matter (DM). In this scenario the momentum distribution of the produced DM particles is usually taken to be the one obtained at reheating, redshifted at later times due to the expansion of the Universe. However, since in such a scenario both the DM and the standard model (SM) fields couple to the inflaton, the DM particles necessarily undergo self-scatterings, as well as elastic and inelastic scattering reactions with the SM bath, all of which proceed through $s$-channel or $t$-channel inflaton exchange. We compute the momentum distribution of the DM particles including the effect of these scatterings, and find that the distributions can be significantly altered, even though DM remains nonthermal throughout the cosmological evolution. We observe that if the inflaton dominantly couples to the SM Higgs boson through a renormalizable interaction, then reheating temperatures and inflaton masses at the TeV scale lead to a large effect from the scattering processes, with the DM-inflaton coupling constrained by the DM density. The scattering effects are found to be sensitive to the duration of the reheating process—larger the duration, more momentum modes are filled at reheating, leading to an enhanced scattering probability. We also obtain the free-streaming length of such DM using the resulting nonthermal momentum distribution, which can be used to estimate the implications of the Lyman-$\alpha$ constraints on the DM mass. It is observed that in the scenarios considered, including the scattering effects can reduce the DM average velocity at matter-radiation equality, and its free-streaming length, by up to a factor of 40, thereby making the constraints on light DM produced in inflaton decay significantly weaker.

中文翻译：

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暴胀子衰变中产生的暗物质的动量分布：暴胀子介导的散射效应

暴胀后的再加热是暗物质（DM）非热能产生的广泛讨论的机制。在这种情况下，产生的 DM 粒子的动量分布通常被认为是在再加热时获得的，后来由于宇宙的膨胀而发生红移。然而，由于在这种情况下，DM 和标准模型（SM）场都与暴胀子耦合，DM 粒子必然会发生自散射，以及与 SM 浴的弹性和非弹性散射反应，所有这些都通过$s$-渠道或$吨$-渠道暴胀交换。我们计算了 DM 粒子的动量分布，包括这些散射的影响，发现分布可以显着改变，即使 DM 在整个宇宙演化过程中保持非热态。我们观察到，如果暴胀子通过可重整化相互作用主要与 SM 希格斯玻色子耦合，那么 TeV 尺度的再加热温度和暴胀子质量会导致散射过程产生很大的影响，DM-暴胀子耦合受 DM 密度的约束。发现散射效应对再加热过程的持续时间很敏感——持续时间越长，在再加热时填充的动量模式就越多，从而导致散射概率增加。$\alpha$DM 质量的约束。可以观察到，在所考虑的情景中，包括散射效应在内的物质辐射相等时的 DM 平均速度及其自由流动长度最多可降低 40 倍，从而限制了暴胀中产生的光 DM衰减明显减弱。