标题： 三维超新星模型中中子星对流层中的快速中微子味不稳定性 显示英文标题

标题： Fast Neutrino Flavor Instability in the Neutron-star Convection Layer of Three-dimensional Supernova Models

摘要： 超新星（SN）中的中微子可能在坍缩恒星核心附近经历快速风味转换。我们对这一引人注目的可能性进行了详细研究，分析了9和20 Msun的最新三维SN模型的时间依赖性。这两个模型都是基于双矩求解器的多维三风味中微子传输计算得出的，并且都表现出轻子数发射自持不对称性（LESA）。传输解决方案不提供中微子通量的角度分布，这对于追踪快速风味不稳定性至关重要。为了克服这一限制，我们使用了一种最近提出的基于能量积分电子轻子数分布角度矩的方法。通过这种方法，我们发现半径<~20公里处存在快速中微子风味不稳定的可能，这位于中微子球内部。我们的结果证实了在二维SN模型以及具有固定物质背景的二维/三维模型中的近期观察结果，这些模型是使用玻尔兹曼中微子传输计算得出的。然而，如前所述，风味不稳定的位置并不是孤立的点，而是围绕着电子反中微子比电子中微子更丰富的体积的薄层。这些体积随时间增长，并首先出现在原中子星（PNS）的对流层中，在那里电子分数（Ye）降低和高温有利于出现负中微子化学势的区域。由于在LESA偶极方向上Ye保持较高，其中从非对流PNS核心向外的对流轻子数传输减缓了去轻子化，因此风味不稳定条件在相反半球更加广泛。这种有趣的现象值得进一步研究，因为其对SN建模的影响以及可能对SN动力学和中微子观测的后果目前尚不清楚。（简写） 显示英文摘要

摘要： Neutrinos from a supernova (SN) might undergo fast flavor conversions near the collapsed stellar core. We perform a detailed study of this intriguing possibility, analyzing time-dependent state-of-the-art 3D SN models of 9 and 20 Msun. Both models were computed with multi-D three-flavor neutrino transport based on a two-moment solver, and both exhibit the presence of the lepton-number emission self-sustained asymmetry (LESA). The transport solution does not provide the angular distributions of the neutrino fluxes, which are crucial to track the fast flavor instability. To overcome this limitation, we use a recently proposed approach based on the angular moments of the energy-integrated electron lepton-number distribution. With this method we find the possibility of fast neutrino flavor instability at radii <~20 km, which is well interior to the neutrinosphere. Our results confirm recent observations in a 2D SN model and in 2D/3D models with fixed matter background, which were computed with Boltzmann neutrino transport. However, the flavor unstable locations are not isolated points as discussed previously, but thin skins surrounding volumes where electron antineutrinos are more abundant than electron neutrinos. These volumes grow with time and appear first in the convective layer of the proto-neutron star (PNS), where a decreasing electron fraction (Ye) and high temperatures favor the occurrence of regions with negative neutrino chemical potential. Since Ye remains higher in the LESA dipole direction, where convective lepton-number transport out from the nonconvective PNS core slows down the deleptonization, flavor unstable conditions become more widespread in the opposite hemisphere. This interesting phenomenon deserves further investigation, since its impact on SN modeling and possible consequences for SN dynamics and neutrino observations are presently unclear. (abridged)