三味热轻子生成无需调谐

中文摘要 AI 辅助

我们在Type-I跷跷板的一个扩展中研究热轻子生成，其中实单态标量非对角耦合到右手中微子。相互作用$-y_{ij}\phi N_iN_j$（其中$i\neq j$）在重中微子衰变中引入了新的CP破坏源，而对标准轻子冲蚀的增强可忽略不计。我们推导了标量诱导CP不对称性的解析上界，并使用全味Boltzmann方程和密度矩阵形式给出了数值结果。我们表明，在电弱尺度下，具有层级右手中微子谱可以产生观测到的重子不对称性。在最小Type-I跷跷板中，降低衰变轻子生成尺度通常需要调谐的右手中微子质量准简并，或树级与单圈对轻中微子质量贡献之间的抵消，而层级轻子生成则需要高尺度，这加剧了希格斯层级问题。这种单态标量扩展似乎避免了这些张力，允许在低至电弱尺度下具有层级右手中微子谱的成功轻子生成。

英文摘要

We investigate thermal leptogenesis in an extension of the Type-I seesaw in which a real singlet scalar couples non-diagonally to the right-handed neutrinos. The interactions $-y_{ij}ϕN_iN_j$, with $i\neq j$, introduce new sources of CP violation in heavy-neutrino decays with a negligible enhancement of the standard leptonic washout. We derive an analytic upper bound on the scalar-induced CP asymmetry and present numerical results using fully flavoured Boltzmann equations and the density-matrix formalism. We show that the observed baryon asymmetry can be generated with a hierarchical right-handed-neutrino spectrum at the electroweak scale. In the minimal Type-I seesaw, lowering the scale of decay leptogenesis typically requires either a tuned quasi-degeneracy of the right-handed-neutrino masses or cancellations between the tree-level and one-loop contributions to the light-neutrino masses, while hierarchical leptogenesis instead requires a high scale that aggravates the Higgs hierarchy problem. This singlet-scalar extension appears to avoid these tensions, allowing successful leptogenesis with a hierarchical right-handed-neutrino spectrum down to the electroweak scale.

发表机构

• School of Physics and Astronomy, University of Southampton（南安普顿大学物理与天文学学院）

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