发表机构
Gran Sasso Science Institute (GSSI); Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Napoli（格兰萨索科学研究所; 意大利国家核物理研究所那不勒斯分部）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究探讨中微子等离子体中集体模式终止的机制，分类了简并点与突然终止两类奇异行为，并证明洛伦兹分布可等价为有效碰撞率，简化色散关系。
AI 中文摘要
中微子等离子体支持味波，即味的集体振荡，当中微子满足切连科夫条件时，它们可以共振发射或吸收这些波。对于无质量中微子，该条件导致色散关系中出现奇异特征：例如，朗道阻尼模式当其相速度接近光速时会突然消失。我们研究了当非零中微子质量引入速度分布时这些奇异性如何变化。我们将频率作为波矢函数的奇异行为分为两类：(i) 简并点，即两个模式合并之处；(ii) 突然的模式终止，即频率接近味介电函数的支点割线时。对于每一类，我们推导了局部展开式并确定了此类行为可能发生的位置。简并点在快速极限下轴对称色散关系中经常遇到，但并不普遍。非零中微子质量沿对称轴提升简并性；在三维波矢空间中，可能仍然存在简并线，这些线不一定与对称轴相交。相反，突然的模式终止普遍存在，除非是特殊的能量分布，即整函数。作为本研究的副产品，我们证明了具有洛伦兹型中微子频率分布的无碰撞等离子体与具有有效碰撞速率的单色等离子体完全等价。因此，将一般频率分布近似为洛伦兹函数的和可以大大简化色散关系。
英文摘要
Neutrino plasmas support flavor waves, collective oscillations of flavor, that neutrinos can resonantly emit or absorb when they fulfill the Cherenkov condition. For massless neutrinos, this condition leads to singular features in the dispersion relation: Landau-damped modes, for example, disappear abruptly as their phase velocity approaches the speed of light. We investigate how these singularities change when nonzero neutrino masses introduce a spread in velocities. We classify singular behavior of the frequency as a function of wavevector into i) degeneracy points, where two modes merge, and ii) abrupt mode termination, when the frequency approaches a branch cut of the flavor dielectric function. For each class, we derive a local expansion and determine where such behavior can occur. Degeneracy points, frequently encountered in axially symmetric dispersion relations in the fast limit, are not generic. Nonzero neutrino masses lift the degeneracy along the symmetry axis; in three-dimensional wavevector space, there might still be degeneracy lines, not necessarily intersecting the symmetry axis. Abrupt mode termination, instead, persists generically, except for special energy distributions which are entire functions. As a byproduct of this study, we show that a collisionless plasma with a Lorentzian neutrino-frequency distribution is exactly equivalent to a monochromatic one with an effective collision rate. Approximating a general frequency distribution by a sum of Lorentzians therefore substantially simplifies the dispersion relation.
Comments27 pages, 10 figures
