本文研究了非标准宇宙学历史下紫外冻结产生暗物质的机制，发现脱离瞬时衰变近似时最高温度 T max 会通过增强因子提升暗物质丰度，且该效应的临界质量维度与增强指数取决于再加热前的物态方程。
摘要：
紫外冻结产生的一个显著特征是遗留密度强烈依赖于热浴的最高温度，而一个常见的假设是，相关的“最高温度”应是暴胀后的再加热温度 $T_\ ext{RH}$。然而，在某些场景下热浴的温度可能显著更高，达到记为 T max 的值，这一事实只有在脱离瞬时衰变近似时才显现出来。有趣的是，已有研究表明，如果算子具有足够高的质量维度，那么相对于假设瞬时再加热的朴素估计，暗物质丰度可以通过一个依赖于 ($T_\ ext{max}/T_\ ext{RH}$) 的“增强因子”得到提升。我们在此强调，在非标准宇宙学历史中，瞬时衰变近似失效时的算子临界质量维度，以及增强因子的指数，均取决于再加热之前的物态方程 $ω$。我们重点介绍了四个例子，在这些例子中，暗物质丰度在引力子暗物质、模门户、Higgs 门户以及自旋-2 门户（可能出现在双度规引力模型中）的背景下获得了显著增强。我们还对从运动主导到辐射主导的转变作为非标准宇宙学的一个典型例子进行了评述。
英文摘要：
A notable feature of UV freeze-in is that the relic density is strongly dependent on the highest temperatures of the thermal bath, and a common assumption is that the relevant 'highest temperature' should be the reheating temperature after inflation $T_\text{RH}$. However, the temperature of the thermal bath can be significantly higher in certain scenarios, reaching a value denoted T max , a fact which is only apparent away from the instantaneous decay approximation. Interestingly, it has been shown that if the operators are of sufficiently high mass dimension then the dark matter abundance can be enhanced by a 'boost factor' depending on ($T_\text{max}/T_\text{RH}$) relative to naive estimates assuming instantaneous reheating. We highlight here that in non-standard cosmological histories the critical mass dimension of the operator above at which the instantaneous decay approximation breaks down, and the exponent of the boost factor, depend on the equation of state $ω$ prior to reheating. We highlight four examples in which the dark matter abundance receives a significant enhancement in the context of gravitino dark matter, the moduli portal, the Higgs portal, and the spin-2 portal (as might arise in bimetric gravity models). We comment on the transition from kination domination to radiation domination as a motivated example of non-standard cosmologies.
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We study a class of models in which the Standard Model (SM) and dark matter (DM) belong to a conformal/scale-invariant theory at high energies. Scale invariance is spontaneously broken at scale $f$, giving rise to a dilaton as the corresponding Goldstone boson. In the low energy theory, we assume that DM interacts with the SM solely through the dilaton portal, which is suppressed by the conformal breaking scale $f$. For $f\gg{\rm TeV}$, the portal interactions are extremely weak, resulting in DM not being in thermal equilibrium with the SM. Thus, ultraviolet freeze-in production of DM occurs t…
Genesis of baryon and dark matter asymmetries through ultraviolet scattering freeze-in
Institute for Fundamental Science and Department of Physics, University of Oregon（俄勒冈大学基础物理研究所与物理系）；Center for Theoretical Physics – a Leinweber Institute, Massachusetts Institute of Technology（麻省理工学院莱因韦伯理论物理中心）；Department of Physics, Harvard University（哈佛大学物理系）；TRIUMF（特里尔姆夫国家粒子加速器中心）；Department of Physics and Astronomy, University of California, Riverside（加州大学河滨分校物理与天文系）
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Rotating black holes (BHs) can efficiently transfer energy to the surrounding environment via superradiance. In particular, when the Compton length of a particle is comparable to the gravitational radius of a BH, the particle's occupation number can be exponentially amplified. In this work, we investigate the effect of the primordial-black-hole (PBH) superradiant instabilities on the generation of heavy bosonic dark matter (DM) with mass above $\sim$ 1 TeV. Additionally, we analyze its interplay with other purely gravitational and therefore unavoidable DM production mechanisms such as Hawking …
If the reheating temperature at the end of inflation is low, of order 10 MeV, then dark matter produced through ultraviolet freeze-in has a large direct detection cross section. We study such a scenario in which dark matter is hadrophilic. This leads to dark matter-nucleon scattering cross sections of interest for near-future experiments for dark matter masses in the range of 100 keV-100 MeV. We explore how these predictions vary if reheating is non-instantaneous.
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