A neutron star harbors 𝒪(10⁵⁶) electrons in its core, and almost the same number of muons, with muon decay prohibited by Pauli blocking. However, as macroscopic properties of the star such as its mass, rotational velocity, or magnetic field evolve over time, the equilibrium lepton abundances (dictated by the weak interactions) change as well. Scenarios where this can happen include spin-down, accretion, magnetic field decay, and tidal deformation. We discuss the mechanisms by which a star disrupted in one of these ways re-establishes lepton chemical equilibrium. In most cases, the dominant processes are out-of-equilibrium Urca reactions, the rates of which we compute for the first time. If, however, the equilibrium muon abundance decreases, while the equilibrium electron abundance increases (or decreases less than the equilibrium muon abundance), outward diffusion of muons plays a crucial role as well. This is true in particular for stars older than about 10⁴ yrs whose core has cooled to ≲ 20 keV. The muons decay in a region where Pauli blocking is lifted, and we argue that these decays lead to a flux of 𝒪(10 MeV) neutrinos. Realistically, however, this flux will remain undetectable for the foreseeable future.

中文翻译：

---

超越化学平衡的中子星中的电子和 μ 子动力学


中子星的核心含有 O（10⁵⁶） 个电子，以及几乎相同数量的 μ 子，泡利阻塞阻止了 μ 子衰变。然而，随着恒星的宏观特性（如质量、旋转速度或磁场）随着时间的推移而变化，平衡轻子丰度（由弱相互作用决定）也会发生变化。可能发生这种情况的情况包括自旋下降、吸积、磁场衰减和潮汐变形。我们讨论了以这些方式之一被破坏的恒星重新建立轻子化学平衡的机制。在大多数情况下，主要过程是失衡的 Urca 反应，我们首次计算了其速率。然而，如果平衡 μ 子丰度降低，而平衡电子丰度增加（或减少幅度小于平衡 μ 子丰度），则 μ 子的向外扩散也起着至关重要的作用。对于年龄超过 10^{到 4} 年的恒星来说尤其如此，这些恒星的核心已经冷却到 ≲ 20 keV。μ 子在 Pauli 阻塞解除的区域衰变，我们认为这些衰变导致 O（10 MeV） 中微子的通量。然而，实际上，在可预见的未来，这种变化仍然无法被检测到。