由长程相互作用暗物质引发的天体物理等离子体不稳定性
Astrophysical Plasma Instabilities induced by Long-Range Interacting Dark Matter
AI总结：
本文研究长程相互作用暗物质在宇宙和星系团环境中的等离子体不稳定性，发现韦贝尔和火蛇不稳定性可显著改变子弹星系团并合性质，并对毫电荷及暗电荷暗物质参数空间给出更严格约束。
摘要：
如果暗物质（DM）带有毫电荷或暗电荷，集体等离子体过程可能在动量交换中主导直接粒子碰撞。等离子体流动不稳定性可以将暗物质的动量耦合到反向流动的重子或其他暗物质上，并导致反向流动的流体彼此静止，正如天体物理系统中重子无碰撞激波所发生的情况。虽然当暗物质带有毫电荷时，静电等离子体不稳定性被朗道阻尼强烈抑制，但在相关的宇宙学情形中，假设线性不稳定性以重子等离子体中通常发现的方式饱和，电磁不稳定性（例如韦贝尔不稳定性）可以耦合动量。我们发现，在复合之前的宇宙中，暗物质的流动受到直接碰撞的影响比集体过程更强，这验证了先前的约束。然而，当考虑磁化韦贝尔不稳定性和火蛇不稳定性时，如果 $[q_χ/m_χ] \gtrsim 10^{-12}-10^{-11}$，子弹星系团并合的性质可能会发生实质性改变，其中 $[q_χ/m_χ]$ 是暗物质相对于质子的荷质比。在暗 $U(1)$ 电荷的情况下，韦贝尔增长率甚至更快，可能在子弹星系团系统中排除 $[q_χ/m_χ] \gtrsim 10^{-14}$，这与先前的工作一致。先前对毫电荷暗物质（mDM）的最强限制来自考虑星系盘的减速。我们表明，等离子体不稳定性或纠缠的背景磁场可能导致暗物质的扩散传播，从而削弱这些减速限制。因此，等离子体不稳定性可能在毫电荷暗物质的大部分参数空间上施加一些最严格的约束，并且我们的结果证实了先前对暗电荷参数空间的极其严格的潜在约束。
英文摘要：
If dark matter (DM) is millicharged or darkly charged, collective plasma processes may dominate momentum exchange over direct particle collisions. Plasma streaming instabilities can couple the momentum of the DM to counter-streaming baryons or other DM and result in the counter-streaming fluids coming to rest with each other, just as happens for baryonic collisionless shocks in astrophysical systems. While electrostatic plasma instabilities are highly suppressed by Landau damping when DM is millicharged, in the cosmological situations of interest, electromagnetic instabilities such as the Weibel can couple momenta, assuming that the linear instability saturates in the manner typically found for baryonic plasmas. We find that the streaming of DM in the pre-Recombination universe is affected more strongly by direct collisions than collective processes, validating previous constraints. However, when considering magnetized Weibel and Firehose instabilities, the properties of the Bullet Cluster merger are likely to be substantially altered if $[q_χ/m_χ] \gtrsim 10^{-12}-10^{-11}$, where $[q_χ/m_χ]$ is the charge-to-mass ratio of the DM relative to that of the proton. The Weibel growth rates are even faster in the case of a dark-$U(1)$ charge, potentially ruling out $[q_χ/m_χ] \gtrsim 10^{-14}$ in the Bullet Cluster system, in agreement with previous work. The strongest previous limits on millicharged DM (mDM) arise from considering the spin-down of galactic disks. We show that plasma instabilities or tangled background magnetic fields could lead to diffusive propagation of the DM, weakening these spin-down limits. Thus, plasma instabilities may place some of the most stringent constraints over much of the millicharged, and our results corroborate previous extremely stringent potential constraints on the dark-charged parameter space.
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