{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/dirac-neutrinos-and-n-rm-eff-ii-the-freeze-in","title":"Dirac neutrinos and $N_{\\rm eff}$ II: the freeze-in case","arxiv_id":"2011.13059","date":"2020-11-25","proceeding":null,"authors":["Xuheng Luo","Werner Rodejohann","Xun-Jie Xu"],"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.","url_abs":"https://arxiv.org/abs/2011.13059v1","url_pdf":"https://arxiv.org/pdf/2011.13059v1.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"dirac-neutrinos-and-n-rm-eff-ii-the-freeze-in","repo_url":"https://github.com/xunjiexu/Thermal_Monte_Carlo","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":1,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}