发表机构
Università del Salento; INFN-Istituto Nazionale di Fisica Nucleare, Sezione di Lecce; University of Sussex（萨伦托大学; 意大利国家核物理研究所莱切分部; 萨塞克斯大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究首次探究蒸发原初黑洞对狄拉克轻子生成机制的修改，发现其可扩展中介体质量的成功范围并补偿小CP不对称性，还会影响ΔN_eff。
AI 中文摘要
狄拉克轻子生成机制为重子不对称性提供了一种性质不同的产生途径：轻子总轻子数守恒，但在标准模型与右旋中微子领域存储着大小相等、方向相反的不对称性，仅可见部分由电弱 Sphalerons 处理。我们首次专门研究了蒸发原初黑洞（Primordial Black Holes, PBHs）如何修改这一机制。在最小带电标量中介体框架下，我们求解耦合玻尔兹曼系统，该系统包含热产生、中介体X及右旋中微子的霍金辐射、PBH对膨胀率的贡献以及熵注入。研究发现，霍金辐射可在热产生效率低下的区域填充X，使其后续的CP破坏衰变能够增强重子不对称性。在代表性基准场景中，PBHs将成功区域从中介体质量约10^9 GeV扩展至约10^6 GeV，且可补偿较小的有效CP不对称性。该效应并非普适：当热狄拉克轻子生成机制已高效运作时，PBHs反而会降低最终不对称性。PBH蒸发还会向右旋中微子领域沉积能量，并对ΔN_eff产生贡献。在PBH参数扫描中，能重现观测到的重子不对称性的部分区域位于普朗克参考水平ΔN_eff=0.284以下，且在计划中的CMB-S4灵敏度ΔN_eff=0.06以上。
英文摘要
Dirac leptogenesis offers a qualitatively different route to the baryon asymmetry: total lepton number is conserved, but equal and opposite asymmetries are stored in the Standard Model and right handed neutrino sectors, with only the visible component processed by electroweak sphalerons. We present the first dedicated study of how evaporating primordial black holes (PBHs) modify this mechanism. In a minimal charged-scalar mediator setup, we solve the coupled Boltzmann system including thermal production, Hawking emission of the mediator $X$ and of right handed neutrinos, the PBH contribution to the expansion rate, and entropy injection. We find that Hawking emission can populate $X$ in regions where thermal production is inefficient, allowing its subsequent CP-violating decays to enhance the baryon asymmetry. For representative benchmarks, PBHs extend the successful region from mediator masses around $10^9\,{\rm GeV}$ down to about $10^6\,{\rm GeV}$ and can compensate for smaller effective CP asymmetries. This effect is not universal: where thermal Dirac leptogenesis is already efficient, PBHs can instead reduce the final asymmetry. Their evaporation also deposits energy in the right handed neutrino sector and contributes to $ΔN_{\rm eff}$. In the PBH parameter scan, part of the region that reproduces the observed baryon asymmetry lies below the Planck reference level $ΔN_{\rm eff}=0.284$ and above the projected CMB-S4 sensitivity $ΔN_{\rm eff}=0.06$.
Comments41 pages (including Appendices); 7 figures + References
