中等密度下中微子振荡的同步与退相干
Synchronization vs. decoherence of neutrino oscillations at intermediate densities
摘要：
研究了具有任意固定密度的双味中微子系统的集体振荡。在真空极限，具有不同能量的模式快速退相（运动学退相干），而在无限密度的极限，它们彼此锁定（同步）。对于中间密度，我们发现不同类别的解决方案。在部分同步的意义上，总是存在仅在密度阈值以上发生的相变。对于小的混合角，部分或完全退相干可以由参数共振引起，从而为问题引入新的时间尺度，最终结果取决于光谱和混合角。我们推导出一个解析关系，使我们能够计算后期的相干度的基础上的频谱。
英文摘要：
We study collective oscillations of a two-flavor neutrino system with arbitrary but fixed density. In the vacuum limit, modes with different energies quickly de-phase (kinematical decoherence), whereas in the limit of infinite density they lock to each other (synchronization). For intermediate densities, we find different classes of solutions. There is always a phase transition in the sense of partial synchronization occurring only above a density threshold. For small mixing angles, partial or complete decoherence can be induced by a parametric resonance, introducing a new time scale to the problem, the final outcome depending on the spectrum and mixing angle. We derive an analytic relation that allows us to calculate the late-time degree of coherence based on the spectrum alone.
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