AI 中文总结
本研究检验宇宙学中微子质量约束对热历史的稳健性，发现光子或暗辐射注入及中微子丰度变化仅使质量上限偏移至多0.004 eV，且中微子温度与质量正相关，降低辐射密度会加剧现有张力。
AI 中文摘要
我们研究了宇宙学对中微子质量的约束如何依赖于假定的宇宙热历史。中微子脱耦后的光子注入会降低从宇宙微波背景（CMB）温度推断出的中微子丰度，从而可能放宽对中微子质量的上限。我们首先评估了在太初核合成之后，大质量粒子衰变为光子和暗辐射对宇宙学中微子质量约束的改变。为了更普遍地检验这一约束的稳健性，我们还评估了在不假设特定物理机制的情况下改变宇宙中微子背景温度的影响。我们使用来自Planck的初级CMB观测、Planck和ACT的CMB透镜测量以及DESI的重子声学振荡数据，对这两种框架进行了MCMC分析。对于简并质量排序，95%置信度上限从标准热历史中的$\sum m_\nu<0.0691$ eV收紧到仅衰变为光子时的大质量粒子情形下的$\sum m_\nu<0.0652$ eV，而除了光子外还注入暗辐射则略微放宽该上限至$\sum m_\nu<0.0710$ eV。同样的模式也适用于正常和倒转排序，并且在固定质量分裂的情况下，衰变情景使中微子质量之和的约束最多偏移0.004 eV。允许与模型无关的中微子-光子比变化，对于简并排序，95%置信度上限为$\sum m_\nu<0.0724$ eV，这表明我们中微子质量约束的严格性并非由对衰变情景的约束所驱动。我们发现中微子温度与中微子质量之和呈正相关，这意味着降低复合前辐射密度只会加剧宇宙学中微子质量约束与测量到的质量分裂之间新出现的张力。
英文摘要
We investigate how neutrino-mass constraints from cosmology depend on the assumed thermal history of the universe. Photon injection after neutrino decoupling would decrease the neutrino abundance inferred from the temperature of the cosmic microwave background (CMB), potentially loosening the upper limit on their masses. We first evaluate how the cosmological neutrino-mass bound is altered by the decay of massive particles into photons and dark radiation after Big Bang nucleosynthesis. To test the robustness of this constraint more generally, we also assess the impact of varying the temperature of the cosmic neutrino background without assuming a specific physical mechanism. We perform MCMC analyses of both frameworks with primary CMB observations from Planck, CMB lensing measurements from Planck and ACT, and baryon acoustic oscillation data from DESI. For the degenerate mass ordering, the $95\%$ credible limit tightens from $\sum m_ν<0.0691$ eV in a standard thermal history to $\sum m_ν<0.0652$ eV if the massive particles decay only into photons, while the injection of dark radiation in addition to photons slightly relaxes this limit to $\sum m_ν<0.0710$ eV. The same pattern holds for the normal and inverted orderings, and the decay scenario shifts the bound on the sum of the neutrino masses by at most $0.004$ eV for fixed mass splittings. Allowing model-agnostic changes in the neutrino-to-photon ratio yields a $95\%$ credible limit of $\sum m_ν<0.0724$ eV for the degenerate ordering, indicating that the stringency of our neutrino-mass bounds is not driven by constraints on the decay scenario. We find that the neutrino temperature and the sum of the neutrino masses are positively correlated, which implies that reducing the pre-recombination radiation density will only worsen the emerging tension between cosmological bounds on the neutrino masses and the measured mass splittings.
Comments16 pages plus 8 pages of appendices and references; 15 figures; 9 tables
