Weyl fermion creation by cosmological gravitational wave background at 1-loop
Abstract Weyl fermions of spin 1 2 $$ \frac{1}{2} $$ minimally coupled to Einstein’s gravity in 4 dimensions cannot be produced purely gravitationally in an expanding Universe at tree level. Surprisingly, as we showed in a recent letter [1], this changes at gravitational 1-loop when cosmic perturbat...
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2025-01-01
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| Series: | Journal of High Energy Physics |
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| Online Access: | https://doi.org/10.1007/JHEP01(2025)023 |
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| author | Azadeh Maleknejad Joachim Kopp |
| author_facet | Azadeh Maleknejad Joachim Kopp |
| author_sort | Azadeh Maleknejad |
| collection | DOAJ |
| description | Abstract Weyl fermions of spin 1 2 $$ \frac{1}{2} $$ minimally coupled to Einstein’s gravity in 4 dimensions cannot be produced purely gravitationally in an expanding Universe at tree level. Surprisingly, as we showed in a recent letter [1], this changes at gravitational 1-loop when cosmic perturbations, like a gravitational wave background, are present. Such a background introduces a new scale, thereby breaking the fermions’ conformal invariance. This leads to a non-vanishing gravitational self-energy for Weyl fermions at 1-loop and induces their production. In this paper, we present an extended study of this new mechanism, explicitly computing this effect using the in-in formalism. We work in an expanding Universe in the radiation-dominated era as a fixed background. Gravitational wave-induced fermion production has rich phenomenological consequences. Notably, if Weyl fermions eventually acquire mass, and assuming realistic — and potentially detectable — gravitational wave backgrounds, the mechanism can explain the abundance of dark matter in the Universe. More generally, gravitational-wave induced freeze-in is a new purely gravitational mechanism for generating other feebly interacting fermions, e.g. right-handed neutrinos. We show that this loop level effect can dominate over the conventional — tree-level — gravitational production of superheavy fermions in a sizable part of the parameter space ( https://github.com/koppj/GW-freeze-in/ ). |
| format | Article |
| id | doaj-art-1a6310f6b0e3436b974667efbdb66944 |
| institution | Kabale University |
| issn | 1029-8479 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | SpringerOpen |
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| series | Journal of High Energy Physics |
| spelling | doaj-art-1a6310f6b0e3436b974667efbdb669442025-01-19T12:06:46ZengSpringerOpenJournal of High Energy Physics1029-84792025-01-012025113510.1007/JHEP01(2025)023Weyl fermion creation by cosmological gravitational wave background at 1-loopAzadeh Maleknejad0Joachim Kopp1Department of Physics, King’s College LondonTheoretical Physics Department, CERNAbstract Weyl fermions of spin 1 2 $$ \frac{1}{2} $$ minimally coupled to Einstein’s gravity in 4 dimensions cannot be produced purely gravitationally in an expanding Universe at tree level. Surprisingly, as we showed in a recent letter [1], this changes at gravitational 1-loop when cosmic perturbations, like a gravitational wave background, are present. Such a background introduces a new scale, thereby breaking the fermions’ conformal invariance. This leads to a non-vanishing gravitational self-energy for Weyl fermions at 1-loop and induces their production. In this paper, we present an extended study of this new mechanism, explicitly computing this effect using the in-in formalism. We work in an expanding Universe in the radiation-dominated era as a fixed background. Gravitational wave-induced fermion production has rich phenomenological consequences. Notably, if Weyl fermions eventually acquire mass, and assuming realistic — and potentially detectable — gravitational wave backgrounds, the mechanism can explain the abundance of dark matter in the Universe. More generally, gravitational-wave induced freeze-in is a new purely gravitational mechanism for generating other feebly interacting fermions, e.g. right-handed neutrinos. We show that this loop level effect can dominate over the conventional — tree-level — gravitational production of superheavy fermions in a sizable part of the parameter space ( https://github.com/koppj/GW-freeze-in/ ).https://doi.org/10.1007/JHEP01(2025)023Cosmological modelsCosmology of Theories BSMEarly Universe Particle Physics |
| spellingShingle | Azadeh Maleknejad Joachim Kopp Weyl fermion creation by cosmological gravitational wave background at 1-loop Journal of High Energy Physics Cosmological models Cosmology of Theories BSM Early Universe Particle Physics |
| title | Weyl fermion creation by cosmological gravitational wave background at 1-loop |
| title_full | Weyl fermion creation by cosmological gravitational wave background at 1-loop |
| title_fullStr | Weyl fermion creation by cosmological gravitational wave background at 1-loop |
| title_full_unstemmed | Weyl fermion creation by cosmological gravitational wave background at 1-loop |
| title_short | Weyl fermion creation by cosmological gravitational wave background at 1-loop |
| title_sort | weyl fermion creation by cosmological gravitational wave background at 1 loop |
| topic | Cosmological models Cosmology of Theories BSM Early Universe Particle Physics |
| url | https://doi.org/10.1007/JHEP01(2025)023 |
| work_keys_str_mv | AT azadehmaleknejad weylfermioncreationbycosmologicalgravitationalwavebackgroundat1loop AT joachimkopp weylfermioncreationbycosmologicalgravitationalwavebackgroundat1loop |