arXiv 2012.090832020-12hep-ph

冻结产生的超相对论范围内的暗物质

Freeze-in produced dark matter in the ultra-relativistic regime

Simone Biondini, Jacopo Ghiglieri

备注：: 43 pages, 14 figures, journal version
发表信息：: JCAP03(2021)075
DOI：: 10.1088/1475-7516/2021/03/075

摘要：

当暗物质粒子只与早期宇宙中的等离子体成分发生微弱的相互作用时，它们永远不会达到热平衡。与冻结机制相反，暗物质丰度在$T \ll M$中确定，弱相互作用态的能量密度在$T \gtrsim M$中积累并增加。在这项工作中，我们解决了高温制度对暗物质生产率的影响，其中暗粒子和标准模型粒子是超相对论性的，几乎是轻的。在这种设置中，多个软散射，以及$2 \to 2$过程，被发现给生产率的贡献很大。在模型中，我们认为在这项工作中，即一个马约拉纳费米子暗物质的质量$M$伴随着一个较重的标量$-$与质量分裂$ΔM$ $-$的股份与可见光的部门的相互作用，能量密度可以大大低估时，忽略了高温动力学。我们发现，整体有效的$1 \leftrightarrow 2$和$2 \to2$高温贡献的暗物质生产给$\mathcal{O}(10)$（20\%）的修正$ΔM /M =0.1$（$ΔM /M =10$）的玻恩生产率与真空质量和矩阵元素。我们还评估了束缚态效应对较重标量后期湮灭的影响，在超弱相互作用机制的背景下。

英文摘要：

When dark matter particles only feebly interact with plasma constituents in the early universe, they never reach thermal equilibrium. As opposed to the freeze-out mechanism, where the dark matter abundance is determined at $T \ll M$, the energy density of a feebly interacting state builds up and increases over $T \gtrsim M$. In this work, we address the impact of the high-temperature regime on the dark matter production rate, where the dark and Standard Model particles are ultra-relativistic and nearly light-like. In this setting, multiple soft scatterings, as well as $2 \to 2$ processes, are found to give a large contribution to the production rate. Within the model we consider in this work, namely a Majorana fermion dark matter of mass $M$ accompanied by a heavier scalar $-$ with mass splitting $ΔM$ $-$ which shares interactions with the visible sector, the energy density can be dramatically underestimated when neglecting the high-temperature dynamics. We find that the overall effective $1 \leftrightarrow 2$ and $2 \to2$ high-temperature contributions to dark-matter production give $\mathcal{O}(10)$ (20\%) corrections for $ΔM /M =0.1$ ($ΔM /M =10$) to the Born production rate with in-vacuum masses and matrix elements. We also assess the impact of bound-state effects on the late-time annihilations of the heavier scalar, in the context of the super-WIMP mechanism.

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