Consistent $N_{\rm eff}$ fitting in big bang nucleosynthesis analysis
Fuente:
arXiv
Salvato in:
| Autori principali: | , , |
|---|---|
| Natura: | Preprint |
| Pubblicazione: |
2025
|
| Soggetti: | |
| Accesso online: | |
| Tags: |
Aggiungi Tag
Nessun Tag, puoi essere il primo ad aggiungerne!!
|
| _version_ | 1866914504184430592 |
|---|---|
| author | Ganguly, Sougata Jung, Tae Hyun Yun, Seokhoon |
| author_facet | Ganguly, Sougata Jung, Tae Hyun Yun, Seokhoon |
| contents | The effective number of neutrino species, $N_{\rm eff}$, serves as a key fitting parameter extensively employed in cosmological studies. In this work, we point out a fundamental inconsistency in the conventional treatment of $N_{\rm eff}$ in big bang nucleosynthesis (BBN), particularly regarding its applicability to new physics scenarios where $ΔN_{\rm eff}$, the deviation of $N_{\rm eff}$ from the standard BBN prediction, is negative. To ensure consistent interpretation, it is imperative to either restrict the allowed range of $N_{\rm eff}$ or systematically adjust neutrino-induced reaction rates based on physically motivated assumptions. As a concrete example, we consider a simple scenario in which a negative $ΔN_{\rm eff}$ arises from entropy injection into the electromagnetic sector due to the decay of long-lived particles after neutrino decoupling. This process dilutes the neutrino density and suppresses the rate of neutrino-driven neutron-proton conversion. Under this assumption, we demonstrate that the resulting BBN constraints on $N_{\rm eff}$ deviate significantly from those obtained by the conventional, but unphysical, extrapolation of dark radiation scenarios into the $ΔN_{\rm eff} < 0$ regime. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_23354 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Consistent $N_{\rm eff}$ fitting in big bang nucleosynthesis analysis Ganguly, Sougata Jung, Tae Hyun Yun, Seokhoon High Energy Physics - Phenomenology Cosmology and Nongalactic Astrophysics The effective number of neutrino species, $N_{\rm eff}$, serves as a key fitting parameter extensively employed in cosmological studies. In this work, we point out a fundamental inconsistency in the conventional treatment of $N_{\rm eff}$ in big bang nucleosynthesis (BBN), particularly regarding its applicability to new physics scenarios where $ΔN_{\rm eff}$, the deviation of $N_{\rm eff}$ from the standard BBN prediction, is negative. To ensure consistent interpretation, it is imperative to either restrict the allowed range of $N_{\rm eff}$ or systematically adjust neutrino-induced reaction rates based on physically motivated assumptions. As a concrete example, we consider a simple scenario in which a negative $ΔN_{\rm eff}$ arises from entropy injection into the electromagnetic sector due to the decay of long-lived particles after neutrino decoupling. This process dilutes the neutrino density and suppresses the rate of neutrino-driven neutron-proton conversion. Under this assumption, we demonstrate that the resulting BBN constraints on $N_{\rm eff}$ deviate significantly from those obtained by the conventional, but unphysical, extrapolation of dark radiation scenarios into the $ΔN_{\rm eff} < 0$ regime. |
| title | Consistent $N_{\rm eff}$ fitting in big bang nucleosynthesis analysis |
| topic | High Energy Physics - Phenomenology Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2507.23354 |