Fast pairwise conversions of neutrinos are predicted to be ubiquitous in neutron star merger remnants with potentially major implications on the nucleosynthesis of the elements heavier than iron. We present the first sophisticated numerical solution of the neutrino flavor evolution above the remnant disk within a (2+1+1) dimensional setup: two spatial coordinates, one angular variable, and time. We look for a steady-state flavor configuration above the remnant disk. Albeit the linear stability analysis predicts flavor instabilities at any location above the remnant disk, our simulations in the non-linear regime show that fast pairwise conversions lead to minimal neutrino mixing (<1%); flavor equilibration is never achieved in our models. Importantly, fast neutrino conversions are more prominent within localized regions near the edges of the (anti)neutrino decoupling surfaces and almost negligible in the polar region of the remnant. Our findings on the role of fast pairwise conversions should be interpreted with caution because of the approximations intrinsic to our setup and advocate for further work within a more realistic framework.

中文翻译：

---

双中子星并合遗迹中快速中微子转换的多维解

预计中微子的快速成对转换在中子星合并残余物中无处不在，这对比铁重的元素的核合成具有潜在的重大影响。我们在 (2+1+1) 维设置中展示了残盘上方中微子风味演化的第一个复杂数值解：两个空间坐标、一个角变量和时间。我们在残盘上方寻找稳态风味配置。尽管线性稳定性分析预测残留圆盘上方任何位置的风味不稳定性，但我们在非线性状态下的模拟表明，快速成对转换导致最小的中微子混合 (<1%)；在我们的模型中从未实现风味平衡。重要的，快速中微子转换在靠近（反）中微子去耦表面边缘的局部区域内更为突出，而在残余物的极区几乎可以忽略不计。我们关于快速成对转换的作用的发现应该谨慎解释，因为我们的设置固有的近似值，并提倡在更现实的框架内进一步工作。