论文标题
狄拉克中微子和$ n _ {\ rm eff} $
Dirac neutrinos and $N_{\rm eff}$
论文作者
论文摘要
如果中微子是狄拉克粒子，则暗示右手中微子$ν_{r} $的存在。这些将有助于早期宇宙中有效数量的相对论中微子物种$ n _ {\ rm eff} $。凭借纯标准模型相互作用，贡献却忽略不计。但是，在存在新的相互作用的情况下，可以显着增强贡献。我们考虑了中微子（标量，伪量表，矢量，轴向矢量和张量）的最一般有效的四边形相互作用，并计算右手中微子对$ n _ _ {\ rm eff} $的贡献。获得$ n _ {\ rm eff} $的Planck 2018测量值，获得了有效的四效耦合的强大约束，对应于$ 10^{ - 5} \ sim10^{ - 3} $的相互作用强度。这将以高达43 TEV及更高的新物理量表翻译。 CMB-S4等未来的实验可以探测或排除有效的4-中微子中微子的有效的4-中微子算子。讨论了避免这一结论的方法。
If neutrinos are Dirac particles the existence of light right-handed neutrinos $ν_{R}$ is implied. Those would contribute to the effective number of relativistic neutrino species $N_{\rm eff}$ in the early Universe. With pure standard model interactions, the contribution is negligibly small. In the presence of new interactions, however, the contribution could be significantly enhanced. We consider the most general effective four-fermion interactions for neutrinos (scalar, pseudo-scalar, vector, axial-vector and tensor), and compute the contribution of right-handed neutrinos to $N_{\rm eff}$. Taking the Planck 2018 measurement of $N_{\rm eff}$, strong constraints on the effective four-fermion coupling are obtained, corresponding to interaction strengths of $10^{-5}\sim10^{-3}$ in units of the Fermi constant. This translates in new physics scales of up to 43 TeV and higher. Future experiments such as CMB-S4 can probe or exclude the existence of effective 4-neutrino operators for Dirac neutrinos. Ways to avoid this conclusion are discussed.
