重中微子的质量极限
Mass limits for heavy neutrinos
摘要：
粒子物理学数据并不排除比$M_Z/2\sim 45$ GeV重的中微子。比这更重的稳定中微子可能通过在遥远星系中的湮灭以及宇宙中的暗物质含量来贡献宇宙伽马射线背景。我们计算了宇宙中重中微子密度随其质量$M_N$的演化，然后计算了来自遥远的$N\bar{N}$（来自$0<z<5$）湮灭的伽马射线谱。数值计算了宇宙中重中微子密度的演化。为了得到宇宙中结构形成引起的增强，我们在GalICS模型中近似$N$的分布与暗物质的分布成正比。将计算的伽马射线谱与测量的EGRET数据进行比较。一个保守的排斥区域的重中微子质量是100至200 GeV，无论是从EGRET数据和我们重新评估的神冈数据。发现重中微子对暗物质的贡献最多为15%。
英文摘要：
Neutrinos heavier than $M_Z/2\sim 45$ GeV are not excluded by particle physics data. Stable neutrinos heavier than this might contribute to the cosmic gamma ray background through annihilation in distant galaxies as well as to the dark matter content of the universe. We calculate the evolution of the heavy neutrino density in the universe as a function of its mass, $M_N$, and then the subsequent gamma ray spectrum from annihilation of distant $N\bar{N}$ (from $0<z<5$). The evolution of the heavy neutrino density in the universe is calculated numerically. In order to obtain the enhancement due to structure formation in the universe, we approximate the distribution of $N$ to be proportional to that of dark matter in the GalICS model. The calculated gamma ray spectrum is compared to the measured EGRET data. A conservative exclusion region for the heavy neutrino mass is 100 to 200 GeV, both from EGRET data and our re-evalutation of the Kamiokande data. The heavy neutrino contribution to dark matter is found to be at most 15%.
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