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arXiv 1208.4347astro-ph.COhep-ph
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中微子有效数对MeV暗物质的限制

Limits on MeV Dark Matter from the Effective Number of Neutrinos

Chiu Man Ho, Robert J. Scherrer

摘要:

热暗物质与电子和光子的耦合比与中微子的耦合更强,如果在中微子与热背景退耦后,热暗物质变得非相对论,那么相对于中微子背景,热暗物质将加热电子-光子等离子体。这导致N_eff降低到标准模型值以下,这是当前CMB观测强烈不赞成的结果。取N_eff和中微子退耦温度的保守下界,我们导出了暗物质粒子质量的一个界,其值取决于粒子的自旋和统计特性,m_x> 3-9 MeV。对于p-波湮灭,我们对暗物质粒子质量的限制强于由复合时期附近的湮灭产生的CMB波动谱的扭曲所产生的限制。

英文摘要:

Thermal dark matter that couples more strongly to electrons and photons than to neutrinos will heat the electron-photon plasma relative to the neutrino background if it becomes nonrelativistic after the neutrinos decouple from the thermal background. This results in a reduction in N_eff below the standard-model value, a result strongly disfavored by current CMB observations. Taking conservative lower bounds on N_eff and on the decoupling temperature of the neutrinos, we derive a bound on the dark matter particle mass of m_χ> 3-9 MeV, depending on the spin and statistics of the particle. For p-wave annihilation, our limit on the dark matter particle mass is stronger than the limit derived from distortions to the CMB fluctuation spectrum produced by annihilations near the epoch of recombination.

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