Fast flavor instability in hypermassive neutron star disk outflows
Fast flavor instability in hypermassive neutron star disk outflows
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DOI：
10.1103/physrevd.106.103003
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发表时间：
2022-07
影响因子：
5
通讯作者：
Rodrigo Fern'andez;S. Richers;Nicole Mulyk;Steven Fahlman
中科院分区：
文献类型：
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作者：
Rodrigo Fern'andez;S. Richers;Nicole Mulyk;Steven Fahlman
我们考察了中微子快速味道不稳定性(FFI)对中子星合并后形成的吸积盘的长期质量抛射的影响。中微子在圆盘中的发射和吸收决定了圆盘喷射物的组成，随后经历了膨胀和冷却时的核合成过程。在这里，我们对变寿命的超大质量中子星(HMNSS)周围的吸积盘进行了28个含时的轴对称粘性流体动力学模拟，分别采用三组分中微子泄漏方案和环形灯泡吸收方案。我们通过改变吸收的中微子通量和温度，在不同的味道平衡水平上允许味道混合，并以一种旨在尊重中微子自相互作用哈密顿量的保持轻子数对称性的方式，以参数方式包括由于FFI引起的中微子味道变换。我们发现，对于迅速形成的黑洞(BH)，由于中微子吸收的减少，FFI降低了圆盘流出的平均电子分数，这主要是由于味道混合时电子中微子/反中微子通量的下降。对于长寿命的HMN，圆盘比BH发射更多的重轻子中微子，重新吸收更多的电子中微子，在味道混合时，较高的中微子温度补偿了较小的通量下降。由此产生的外流具有更宽的电子分数分布，更富质子的峰，并经历更强的辐射驱动。具有中间HMN生存期的磁盘显示的结果介于这两个限制之间。在大多数情况下，FFI对流出的影响是温和的，质量抛射、平均速度和平均电子分数的变化约为$sim 1 0$，而镧系元素/鳗系元素的质量分数的变化可达1倍。
We examine the effect of neutrino flavor transformation by the fast flavor instability (FFI) on long-term mass ejection from accretion disks formed after neutron star mergers. Neutrino emission and absorption in the disk set the composition of the disk ejecta, which subsequently undergoes $r$-process nucleosynthesis upon expansion and cooling. Here we perform 28 time-dependent, axisymmetric, viscous-hydrodynamic simulations of accretion disks around hypermassive neutron stars (HMNSs) of variable lifetime, using a 3-species neutrino leakage scheme for emission and an annular-lightbulb scheme for absorption. We include neutrino flavor transformation due the FFI in a parametric way, by modifying the absorbed neutrino fluxes and temperatures, allowing for flavor mixing at various levels of flavor equilibration, and also in a way that aims to respect the lepton-number preserving symmetry of the neutrino self-interaction Hamiltonian. We find that for a promptly-formed black hole (BH), the FFI lowers the average electron fraction of the disk outflow due to a decrease in neutrino absorption, driven primarily by a drop in electron neutrino/antineutrino flux upon flavor mixing. For a long-lived HMNS, the disk emits more heavy lepton neutrinos and reabsorbs more electron neutrinos than for a BH, with a smaller drop in flux compensated by a higher neutrino temperature upon flavor mixing. The resulting outflow has a broader electron fraction distribution, a more proton-rich peak, and undergoes stronger radiative driving. Disks with intermediate HMNS lifetimes show results that fall in between these two limits. In most cases, the impact of the FFI on the outflow is moderate, with changes in mass ejection, average velocity, and average electron fraction of order $\sim 10\%$, and changes in the lanthanide/actinide mass fraction of up to a factor $\sim 2$.