arXiv 1907.079732019-07hep-ph

通过UV和IR冻结的费米暗物质及其可能的X射线特征

Fermionic dark matter via UV and IR freeze-in and its possible X-ray signature

Anirban Biswas, Sougata Ganguly, Sourov Roy

备注：: 40 pages, 7 figures, 1 table, additional production channels are added, three new appendices are added, new references are included, minor modifications in results and conclusions, version published in JCAP
发表信息：: JCAP03 (2020) 043
DOI：: 10.1088/1475-7516/2020/03/043

摘要：

在过去的十年中，在各种直接探测实验中没有观察到任何暗物质特征，这表明非常流行的WIMP范式可能不是粒子暗物质的实际理论。通过冻结产生的非热暗物质是一个有吸引力的提议，自然地解释了凭借其与标准模型（SM）粒子的弱耦合而产生的零结果。本文考虑SM的一个极小扩张，它是由两个规范单态场构成的，即一个$\mathbb{Z}_2$ -奇费米子$χ$和一个赝标量场$\tildeϕ$，其中前者只在5维及更高的水平上与SM粒子相互作用.这引入了自然抑制的$χ$的相互作用，由一个沉重的新的物理尺度$Λ$和部队$χ$是一个非热暗物质的候选人。我们详细研究了$χ$的制备，同时考虑了紫外（UV）、红外（IR）以及紫外-红外混合冻入，发现对于$10^{10}{\rm GeV}\leqΛ\leq 10^{15}{\rm GeV}$，当再加热温度为$T_{RH}\gtrsim 10^4$ GeV时，$χ$主要通过紫外和紫外-红外混合冻入产生，而低于该温度时，$χ$主要通过红外和紫外-红外混合冻入产生。此外，我们还考虑了级联湮没$χ\barχ \rightarrow \tildeϕ\tildeϕ\rightarrow 4γ$，以解决长期$\sim3.5$ keV X射线线观察到的各种星系和星系团。我们已经发现，长寿命的中间态$\tildeϕ$修改暗物质密度银河系中心附近的有效密度$ρ_{eff}$强烈依赖于$\tildeϕ$的衰变长度。最后，通过与XMM Newton观测的银河系中心X射线通量在$2σ$范围内的比较，得到了$Λ-g$平面上的允许参数空间（$g$是$χ\barχ$和$\tildeϕ$之间的耦合）.

英文摘要：

Non-observation of any dark matter signature at various direct detection experiments over the last decade keeps indicating that immensely popular WIMP paradigm may not be the actual theory of particle dark matter. Non-thermal dark matter produced through freeze-in is an attractive proposal, naturally explaining null results by virtue of its feeble couplings with the Standard Model (SM) particles. We consider a minimal extension of the SM by two gauge singlet fields namely, a $\mathbb{Z}_2$-odd fermion $χ$ and a pseudo scalar $\tildeϕ$, where the former has interactions with the SM particles only at dimension five level and beyond. This introduces natural suppression in the interactions of $χ$ by a heavy new physics scale $Λ$ and forces $χ$ to be a non-thermal dark matter candidate. We have studied production of $χ$ in detail taking into account both ultra-violate (UV), infra-red (IR) as well as mixed UV-IR freeze-in and found that for $10^{10}{\rm GeV}\leqΛ\leq 10^{15}{\rm GeV}$, $χ$ is dominantly produced via UV and mixed UV-IR freeze-in when reheat temperature $T_{RH}\gtrsim 10^4$ GeV and below which the production is dominated by IR and mixed freeze-in. Furthermore, we have considered the cascade annihilation $χ\barχ \rightarrow \tildeϕ\tildeϕ\rightarrow 4γ$ to address the longstanding $\sim3.5$ keV X-ray line observed from various galaxies and galaxy clusters. We have found that the long-lived intermediate state $\tildeϕ$ modifies dark matter density around the galactic centre to an effective density $ρ_{eff}$ which strongly depends on the decay length of $\tildeϕ$. Finally, the allowed parameter space in $Λ-g$ plane ($g$ is the coupling between $χ\barχ$ and $\tildeϕ$) is obtained by comparing our result with the XMM Newton observed X-ray flux from the centre of Milky Way galaxy in $2σ$ range.

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