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Dirac neutrinos and Neff II: the freeze-in case

MPS-Authors

Rodejohann,  Werner
Werner Rodejohann - ERC Starting Grant, Junior Research Groups, MPI for Nuclear Physics, Max Planck Society;

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Xu,  Xunjie
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

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2011.13059.pdf
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Citation

Luo, X., Rodejohann, W., & Xu, X. (2021). Dirac neutrinos and Neff II: the freeze-in case. Journal of Cosmology and Astroparticle Physics, 2021: 082. doi:10.1088/1475-7516/2021/03/082.


Cite as: https://hdl.handle.net/21.11116/0000-0009-032C-3
Abstract
We discuss Dirac neutrinos whose right-handed component $\nu_R$ has new
interactions that may lead to a measurable contribution to the effective number
of relativistic neutrino species $N_{\rm eff}$. We aim at a model-independent
and comprehensive study on a variety of possibilities. Processes for
$\nu_R$-genesis from decay or scattering of thermal species, with spin-0,
spin-1/2, or spin-1 initial or final states are all covered. We calculate
numerically and analytically the contribution of $\nu_R$ to $N_{\rm eff}$
primarily in the freeze-in regime, since the freeze-out regime has been studied
before. While our approximate analytical results apply only to freeze-in, our
numerical calculations work for freeze-out as well, including the transition
between the two regimes. Using current and future constraints on $N_{\rm eff}$,
we obtain limits and sensitivities of CMB experiments on masses and couplings
of the new interactions. As a by-product, we obtain the contribution of
Higgs-neutrino interactions, $\Delta N_{\rm eff}^{\rm SM} \approx
7.5\times10^{-12}$, assuming the neutrino mass is 0.1 eV and generated by the
standard Higgs mechanism.