English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We discuss Dirac neutrinos whose right-handed component $\nu_R$ has newinteractions that may lead to a measurable contribution to the effective numberof relativistic neutrino species $N_{\rm eff}$. We aim at a model-independentand 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 calculatenumerically and analytically the contribution of $\nu_R$ to $N_{\rm eff}$primarily in the freeze-in regime, since the freeze-out regime has been studiedbefore. While our approximate analytical results apply only to freeze-in, ournumerical calculations work for freeze-out as well, including the transitionbetween the two regimes. Using current and future constraints on $N_{\rm eff}$,we obtain limits and sensitivities of CMB experiments on masses and couplingsof the new interactions. As a by-product, we obtain the contribution ofHiggs-neutrino interactions, $\Delta N_{\rm eff}^{\rm SM} \approx7.5\times10^{-12}$, assuming the neutrino mass is 0.1 eV and generated by thestandard Higgs mechanism.

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