标题： 密集中微子气体中的味孤子 显示英文标题

标题： Flavor solitons in dense neutrino gases

摘要： 我们考虑在“快速味道极限”（中微子质量消失）下的密集中微子气体。 首次，我们识别出非线性波方程的精确解，形式为孤子。 它们可以以亚光速或超光速传播，后者不违反因果性。 无限速度的孤子是一个均匀解，除了它只摆动一次而不是周期性摆动外，与通常的快速味道摆锤相同。 静态极限中的亚光速孤子对应于一次摆动的“空间摆锤”。 此类解存在的必要条件是“交叉”中微子角度分布。 基于奈奎斯特准则，我们推导出一个新的充分条件，而无需求解色散关系。 这些孤子非常脆弱：它们的不稳定性与单独的均匀中微子气体一样大。 此外，在存在物质的情况下，只有在与物质电流共动的框架中均匀的解才能存活。 一般来说，物质效应不能通过风味空间中的变换消除，而是具有真实的物理影响。 显示英文摘要

摘要： We consider a dense neutrino gas in the "fast-flavor limit" (vanishing neutrino masses). For the first time, we identify exact solutions of the nonlinear wave equation in the form of solitons. They can propagate with both sub- or superluminal speed, the latter not violating causality. The soliton with infinite speed is a homogeneous solution and coincides with the usual fast-flavor pendulum except that it swings only once instead of being periodic. The subluminal soliton in the static limit corresponds to a one-swing "spatial pendulum". A necessary condition for such solutions to exist is a ``crossed'' neutrino angle distribution. Based on the Nyquist criterion, we derive a new sufficient condition without solving the dispersion relation. The solitons are very fragile: they are as unstable as the homogeneous neutrino gas alone. Moreover, in the presence of matter, only the solution survives that is homogeneous in a frame comoving with the matter current. Generally, the matter effect cannot be eliminated by transformations in flavor space, but instead has a real physical impact.