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Dirac neutrinos and N_{{rm eff}} II: the freeze-in case

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arxiv 2011.13059 v2 pith:ZVG5ZUT6 submitted 2020-11-25 hep-ph astro-ph.CO

Dirac neutrinos and N_{{rm eff}} II: the freeze-in case

classification hep-ph astro-ph.CO
keywords contributionfreeze-ininteractionsdiracfreeze-outneutrinoneutrinosobtain
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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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.

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Cited by 4 Pith papers

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