Lepton flavor asymmetries: from the early Universe to BBN
Abstract Large primordial lepton flavor asymmetries with almost vanishing total baryon-minus-lepton number can evade the usual BBN and CMB constraints if neutrino oscillations lead to perfect flavor equilibration. Solving the momentum averaged quantum kinetic equations (QKEs) describing neutrino osc...
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| Format: | Article |
| Language: | English |
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SpringerOpen
2025-06-01
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| Series: | Journal of High Energy Physics |
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| Online Access: | https://doi.org/10.1007/JHEP06(2025)137 |
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| author | Valerie Domcke Miguel Escudero Mario Fernández Navarro Stefan Sandner |
| author_facet | Valerie Domcke Miguel Escudero Mario Fernández Navarro Stefan Sandner |
| author_sort | Valerie Domcke |
| collection | DOAJ |
| description | Abstract Large primordial lepton flavor asymmetries with almost vanishing total baryon-minus-lepton number can evade the usual BBN and CMB constraints if neutrino oscillations lead to perfect flavor equilibration. Solving the momentum averaged quantum kinetic equations (QKEs) describing neutrino oscillations and interactions, we perform the first systematic investigation of this scenario, uncovering a rich flavor structure in stark contradiction to the assumption of simple flavor equilibration. We find (i) a particular direction in flavor space, ∆n e ≃ – 2/3 (– 1)∆n μ for normal (inverted) neutrino mass hierarchy, in which the flavor equilibration is efficient and primordial asymmetries are essentially unconstrained, (ii) a minimal washout factor, ∆ n e 2 BBN $$ {\left.\Delta {n}_e^2\right|}_{\textrm{BBN}} $$ ≤ 0.03 (0.016) ∑ α ∆ n α 2 ini $$ {\left.\Delta {n}_{\alpha}^2\right|}_{\textrm{ini}} $$ yielding a conservative estimate for the allowed primordial asymmetries in a generic flavor direction, and (iii) particularly strong or weak washout if one of the initial flavor asymmetries vanishes due to non-adiabatic muon- or electron-driven MSW transitions. These results open up the possibility of a first-order QCD phase transition facilitated by large lepton asymmetries as well as baryogenesis from large and compensated ∆n e = ∆n μ asymmetries. Our systematic approach of deriving momentum averaged QKEs includes collision terms beyond the damping approximation, energy transfer between the neutrino and electron-photon plasma, and provides a fast and reliable way to investigate the impact of primordial lepton asymmetries at the time of BBN. We publicly release the Mathematica code COFLASY-M on https://github.com/mariofnavarro/COFLASY which solves the QKEs numerically. |
| format | Article |
| id | doaj-art-19df0ce6cde5420c8d96b63b7b7bff30 |
| institution | DOAJ |
| issn | 1029-8479 |
| language | English |
| publishDate | 2025-06-01 |
| publisher | SpringerOpen |
| record_format | Article |
| series | Journal of High Energy Physics |
| spelling | doaj-art-19df0ce6cde5420c8d96b63b7b7bff302025-08-20T03:04:17ZengSpringerOpenJournal of High Energy Physics1029-84792025-06-012025615610.1007/JHEP06(2025)137Lepton flavor asymmetries: from the early Universe to BBNValerie Domcke0Miguel Escudero1Mario Fernández Navarro2Stefan Sandner3Theoretical Physics Department, CERNTheoretical Physics Department, CERNSchool of Physics & Astronomy, University of GlasgowTheoretical Division, Los Alamos National LaboratoryAbstract Large primordial lepton flavor asymmetries with almost vanishing total baryon-minus-lepton number can evade the usual BBN and CMB constraints if neutrino oscillations lead to perfect flavor equilibration. Solving the momentum averaged quantum kinetic equations (QKEs) describing neutrino oscillations and interactions, we perform the first systematic investigation of this scenario, uncovering a rich flavor structure in stark contradiction to the assumption of simple flavor equilibration. We find (i) a particular direction in flavor space, ∆n e ≃ – 2/3 (– 1)∆n μ for normal (inverted) neutrino mass hierarchy, in which the flavor equilibration is efficient and primordial asymmetries are essentially unconstrained, (ii) a minimal washout factor, ∆ n e 2 BBN $$ {\left.\Delta {n}_e^2\right|}_{\textrm{BBN}} $$ ≤ 0.03 (0.016) ∑ α ∆ n α 2 ini $$ {\left.\Delta {n}_{\alpha}^2\right|}_{\textrm{ini}} $$ yielding a conservative estimate for the allowed primordial asymmetries in a generic flavor direction, and (iii) particularly strong or weak washout if one of the initial flavor asymmetries vanishes due to non-adiabatic muon- or electron-driven MSW transitions. These results open up the possibility of a first-order QCD phase transition facilitated by large lepton asymmetries as well as baryogenesis from large and compensated ∆n e = ∆n μ asymmetries. Our systematic approach of deriving momentum averaged QKEs includes collision terms beyond the damping approximation, energy transfer between the neutrino and electron-photon plasma, and provides a fast and reliable way to investigate the impact of primordial lepton asymmetries at the time of BBN. We publicly release the Mathematica code COFLASY-M on https://github.com/mariofnavarro/COFLASY which solves the QKEs numerically.https://doi.org/10.1007/JHEP06(2025)137Early Universe Particle PhysicsNeutrino InteractionsNon-Standard Neutrino Properties |
| spellingShingle | Valerie Domcke Miguel Escudero Mario Fernández Navarro Stefan Sandner Lepton flavor asymmetries: from the early Universe to BBN Journal of High Energy Physics Early Universe Particle Physics Neutrino Interactions Non-Standard Neutrino Properties |
| title | Lepton flavor asymmetries: from the early Universe to BBN |
| title_full | Lepton flavor asymmetries: from the early Universe to BBN |
| title_fullStr | Lepton flavor asymmetries: from the early Universe to BBN |
| title_full_unstemmed | Lepton flavor asymmetries: from the early Universe to BBN |
| title_short | Lepton flavor asymmetries: from the early Universe to BBN |
| title_sort | lepton flavor asymmetries from the early universe to bbn |
| topic | Early Universe Particle Physics Neutrino Interactions Non-Standard Neutrino Properties |
| url | https://doi.org/10.1007/JHEP06(2025)137 |
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