Primordial neutrino asymmetry evolution with full mean-field effects and collisions
Primordial neutrino asymmetry evolution with full mean-field effects and collisions
复制标题
具有完全平均场效应和碰撞的原始中微子不对称演化
DOI：
10.1088/1475-7516/2022/03/065
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发表时间：
2021
影响因子：
6.4
通讯作者：
C. Pitrou
中科院分区：
文献类型：
--
作者：
Julien Froustey;C. Pitrou
中微子振荡和平均场效应极大地丰富了早期宇宙中微子演化的现象学。考虑到这些影响，最显著的是中微子自身相互作用平均场的贡献，我们重新讨论了原始中微子不对称的演化问题，包括首次给出了碰撞的完整表达式，它描述了与电子/正电子的散射和湮灭以及(反)中微子之间的反应。我们证明了绝热平均振荡传递(ATAO)格式的推广，这是一种以前发展起来的没有中微子简并的数值方法，基于这个问题中的大时间尺度分离，足以达到与完全量子动力学方程积分相同的精度，但显著地快于完全量子动力学方程积分。这一近似突出了同步振荡在中微子化学势演化中的作用，特别是在只有两个中微子混合的特殊情况下。特别是，它允许理解是什么控制着振荡的开始和幅度，但也可以理解为什么会有随后的具有更大频率的集体振荡制度。我们还发现，为了不高估碰撞如何减少这些同步振荡，使用完整的碰撞项而不是依赖于类阻尼近似是非常重要的。最后，我们定性地研究了混合参数如何影响最终的中微子组态，特别是我们证明了违反CP的Dirac相不会对最终的N ef和最终的电子(反)中微子谱有实质性的影响，因此不应该影响宇宙学的可观测性。
Neutrino oscillations and mean-field effects considerably enrich the phenomenology of neutrino evolution in the early Universe. Taking into account these effects, most notably the neutrino self-interaction mean-field contribution, we revisit the problem of the evolution of primordial neutrino asymmetries including for the first time the complete expression for collisions, which describe scattering and annihilations with electrons/positrons and reactions among (anti)neutrinos. We show that a generalisation of the adiabatic transfer of averaged oscillations (ATAO) scheme, a numerical method previously developed without neutrino degeneracy and based on the large separation of time scales in this problem, is sufficient to reach the same accuracy as the full quantum kinetic equation integration, but is notably faster. This approximation highlights the physics of synchronous oscillations at play in the evolution of neutrino chemical potentials, especially in the particular case with only two-neutrino mixing. In particular, it allows to understand what controls the beginning and the amplitude of oscillations, but also why there is a subsequent regime of collective oscillations with larger frequencies. We also find that it is very important to use the full collision term instead of relying on damping-like approximations, in order not to overestimate how collisions reduce these synchronous oscillations. Finally we study qualitatively how mixing parameters affect the final neutrino configuration, and in particular we show that the CP-violating Dirac phase cannot substantially affect the final N eff nor the final electronic (anti)-neutrino spectrum, and thus should not affect cosmological observables.