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[论文解读] Dark Matter's secret liaisons: phenomenology of a dark U(1) sector with bound states

Marco Cirelli, Paolo Panci|INFM-OAR (INFN Catania)|Dec 21, 2016
Dark Matter and Cosmic Phenomena参考文献 216被引用 117
一句话总结

本论文分析具有束缚态形成的暗 U(1) 区域，计算 relic density 和间接探测信号，并从宇宙学和天体物理搜索中推导约束。

ABSTRACT

Dark matter (DM) charged under a dark U(1) force appears in many extensions of the Standard Model, and has been invoked to explain anomalies in cosmic-ray data, as well as a self-interacting DM candidate. In this paper, we perform a comprehensive phenomenological analysis of such a model, assuming that the DM abundance arises from the thermal freeze-out of the dark interactions. We include, for the first time, bound-state effects both in the DM production and in the indirect detection signals, and quantify their importance for Fermi, AMS, and CMB experiments. We find that DM in the mass range 1 GeV to 100 TeV, annihilating into dark photons of MeV to GeV mass, is in conflict with observations. Instead, DM annihilation into heavier dark photons is viable. We point out that the late decays of multi-GeV dark photons can produce significant entropy and thus dilute the DM density. This can lower considerably the dark coupling needed to obtain the DM abundance, and in turn relax the existing constraints.

研究动机与目标

  • 动机并研究带有新的暗 U(1) 电荷的暗物质，其介质为一个质量为 m_{V_D} 的暗光子。
  • 在暗区计算遗留丰度（relic abundance），包括束缚态形成与衰变效应。
  • 评估来自 beam dumps、超新星、直接探测和 BBN 的约束。
  • 研究来自伽马射线、反质子和 CMB 各各的间接探测信号。
  • 探讨多 GeV 级暗光子晚期衰变如何稀释 DM 密度并放宽耦合/约束。

提出的方法

  • 指定一个与暗光子 V_D 耦合并通过对超荷混合到超载（hypercharge）的 Dirac 费米子 DM X。
  • 计算包括基态 BSF 通道及其衰变（到 2 个或 3 个 V_D）的湮灭和束缚态形成截面。
  • 描述通过动量混合将暗光子衰变至 SM 状态并确定相应的分支比。
  • 通过要求热冻结（thermal freeze-out）产生观测到的 DM 密度，关联暗区耦合 alpha_D 与 M_DM 和 m_VD。
  • 将束缚态效应并入遗留密度计算并传播到来自宇宙学与间接搜索的约束中。
  • 使用银河系及矮星系的速度分布来评估截面与信号光谱。
Figure 1: DM annihilation directly into dark photons (left), and via the 2-step process of formation and subsequent decay of bound states (right), for the case of para- and ortho- configurations (top and bottom diagrams, respectively). The dark photons $V_{D}$ are produced on-shell and decay into SM
Figure 1: DM annihilation directly into dark photons (left), and via the 2-step process of formation and subsequent decay of bound states (right), for the case of para- and ortho- configurations (top and bottom diagrams, respectively). The dark photons $V_{D}$ are produced on-shell and decay into SM

实验结果

研究问题

  • RQ1束缚态形成如何影响暗 U(1) 模型中 DM 的热 relic abundance？
  • RQ2在包含 BSF 的情况下，(M_DM, m_VD, alpha_D, epsilon) 的哪些区域与宇宙学和天体物理约束相容？
  • RQ3在何种条件下束缚态衰变与暗光子衰变会产生可观的间接探测信号？
  • RQ4晚期更重的暗光子衰变是否能稀释 DM 密度并放宽耦合/约束？
  • RQ5哪些间接探测通道（伽马射线、反质子、CMB）为该情景提供最强约束？

主要发现

  • 在考虑束缚态形成时，达到观测到的 DM 丰度所需的暗耦合减小。
  • 质量在 1 GeV 至 100 TeV 之间、湮灭到 MeV–GeV 暗光子的 DM 将与观测相冲突，而湮灭到更重的暗光子仍然可行。
  • 多 GeV 暗光子的晚期衰变可注入熵并稀释 DM 密度，从而削弱对该模型的约束。
  • 来自 Fermi、AMS-02 与 Planck CMB 数据的间接搜索对参数空间具有显著约束。
  • 分析强调湮灭与 BSF 截面的共振，以及库仑区间与 Yukawa 效应在截面中的重要性。
  • BSF 在矮星和银河系中较为显著，但对 CMB 时代 DM 速度几乎可以忽略。
Figure 2: The parameter space considered in this work. The dark fine structure constant $\alpha_{{D}}$ is determined on this plane, by requiring that the observed DM abundance arises from thermal freeze-out in the dark sector. Below the dashed blue line, the Bohr momentum is larger than the mediator
Figure 2: The parameter space considered in this work. The dark fine structure constant $\alpha_{{D}}$ is determined on this plane, by requiring that the observed DM abundance arises from thermal freeze-out in the dark sector. Below the dashed blue line, the Bohr momentum is larger than the mediator

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