If the interaction rates between the visible and the dark sectors were never strong enough, the observed dark matter relic abundance could have been produced in the early Universe by non-thermal processes. This is what occurs in the so-called freeze-in mechanism. In the simplest version of the freeze-in paradigm, after dark matter is produced from the standard model thermal bath, its abundance is frozen and remains constant. However, thermalization and number-changing processes in the dark sector can have strong impacts, in particular enhancing the dark matter relic abundance by several orders of magnitude. Here we show that this enhancement can be computed from general arguments as the conservation of energy and entropy, independently from the underlying particle physics details of the dark sector. We also note that this result is quite general, and applies to FIMP production independently of being UV- or IR-dominated.

中文翻译：

---

通过热化促进冻结

如果可见光区和暗区之间的相互作用率不够强，那么观测到的暗物质遗迹丰度可能是在早期宇宙中通过非热过程产生的。这就是所谓的冻结机制中发生的情况。在最简单的冻结范式中，暗物质从标准模型热浴中产生后，其丰度被冻结并保持不变。然而，暗区的热化和数量变化过程会产生强烈的影响，特别是将暗物质遗迹的丰度提高几个数量级。在这里，我们表明这种增强可以从作为能量和熵的守恒的一般论点计算，独立于暗区的基本粒子物理细节。我们还注意到这个结果很一般，