Generalising axion-like particle as the curvaton: sourcing primordial density perturbation and non-Gaussianities
Abstract We investigate the non-perturbatively generated axion-like particle (ALP) potential, involving fermions in the dark sector that couple to the ALP, in an early universe cosmological inflationary stage with the ALP being a spectator field. The potential here deviates from the standard cosine...
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SpringerOpen
2024-10-01
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| Series: | European Physical Journal C: Particles and Fields |
| Online Access: | https://doi.org/10.1140/epjc/s10052-024-13330-3 |
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| author | Anish Ghoshal Abhishek Naskar |
| author_facet | Anish Ghoshal Abhishek Naskar |
| author_sort | Anish Ghoshal |
| collection | DOAJ |
| description | Abstract We investigate the non-perturbatively generated axion-like particle (ALP) potential, involving fermions in the dark sector that couple to the ALP, in an early universe cosmological inflationary stage with the ALP being a spectator field. The potential here deviates from the standard cosine nature due to the presence of the two dark sector fermion masses $$m_u$$ m u and $$m_d$$ m d which couple to the ALP. The ALP is a spectator field during inflation but it starts to oscillate and dominates the energy density of the universe after inflation ends, thereby sourcing isocurvature perturbations, while standard curvature fluctuations from the inflaton are assumed to be sub-dominant. Subsequently the ALP decays converting the isocurvature perturbations to adiabatic perturbations thereby acting as the origin of the primordial density perturbations. We identify the parameter space involving the axion decay constant $$f_{\phi }$$ f ϕ , scale of confinement $$\Lambda $$ Λ , ALP mass m and the masses of the fermions, $$m_u$$ m u and $$m_d$$ m d where it can satisfactorily behave as the curvaton and source the observed primordial density perturbation. We also predict local non-Gaussianity signals for bi-spectrum and tri-spectrum $$f_{NL}$$ f NL and $$g_{NL}$$ g NL , as a function of the ratio $$m_u/m_d$$ m u / m d , which are within the allowed range in the latest Planck observations and are detectable with future observations. Particularly we find that the value of $$f_{NL}$$ f NL and $$g_{NL}$$ g NL are dependent on the ratio of $$m_u$$ m u and $$m_d$$ m d : $$f_{NL}$$ f NL is more or less positive for all scenarios except $$m_u = m_d$$ m u = m d and $$g_{NL}$$ g NL is always positive irrespective of the ratio between $$m_u$$ m u and $$m_d$$ m d . The results of our analysis in the limit $$m_u = m_d$$ m u = m d resembles vanilla curvaton scenario while in the limit $$m_u \gg m_d$$ m u ≫ m d resembles pure axion cosine potential. This is because the model has the unique feature where the extra matter in the dark sector determines the nature and shape of the potential. |
| format | Article |
| id | doaj-art-af7553a96974434ab59e8fd31df38580 |
| institution | Kabale University |
| issn | 1434-6052 |
| language | English |
| publishDate | 2024-10-01 |
| publisher | SpringerOpen |
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| series | European Physical Journal C: Particles and Fields |
| spelling | doaj-art-af7553a96974434ab59e8fd31df385802025-02-09T12:51:56ZengSpringerOpenEuropean Physical Journal C: Particles and Fields1434-60522024-10-01841011310.1140/epjc/s10052-024-13330-3Generalising axion-like particle as the curvaton: sourcing primordial density perturbation and non-GaussianitiesAnish Ghoshal0Abhishek Naskar1Faculty of Physics, Institute of Theoretical Physics, University of WarsawDepartment of Physics, Indian Institute of Technology BombayAbstract We investigate the non-perturbatively generated axion-like particle (ALP) potential, involving fermions in the dark sector that couple to the ALP, in an early universe cosmological inflationary stage with the ALP being a spectator field. The potential here deviates from the standard cosine nature due to the presence of the two dark sector fermion masses $$m_u$$ m u and $$m_d$$ m d which couple to the ALP. The ALP is a spectator field during inflation but it starts to oscillate and dominates the energy density of the universe after inflation ends, thereby sourcing isocurvature perturbations, while standard curvature fluctuations from the inflaton are assumed to be sub-dominant. Subsequently the ALP decays converting the isocurvature perturbations to adiabatic perturbations thereby acting as the origin of the primordial density perturbations. We identify the parameter space involving the axion decay constant $$f_{\phi }$$ f ϕ , scale of confinement $$\Lambda $$ Λ , ALP mass m and the masses of the fermions, $$m_u$$ m u and $$m_d$$ m d where it can satisfactorily behave as the curvaton and source the observed primordial density perturbation. We also predict local non-Gaussianity signals for bi-spectrum and tri-spectrum $$f_{NL}$$ f NL and $$g_{NL}$$ g NL , as a function of the ratio $$m_u/m_d$$ m u / m d , which are within the allowed range in the latest Planck observations and are detectable with future observations. Particularly we find that the value of $$f_{NL}$$ f NL and $$g_{NL}$$ g NL are dependent on the ratio of $$m_u$$ m u and $$m_d$$ m d : $$f_{NL}$$ f NL is more or less positive for all scenarios except $$m_u = m_d$$ m u = m d and $$g_{NL}$$ g NL is always positive irrespective of the ratio between $$m_u$$ m u and $$m_d$$ m d . The results of our analysis in the limit $$m_u = m_d$$ m u = m d resembles vanilla curvaton scenario while in the limit $$m_u \gg m_d$$ m u ≫ m d resembles pure axion cosine potential. This is because the model has the unique feature where the extra matter in the dark sector determines the nature and shape of the potential.https://doi.org/10.1140/epjc/s10052-024-13330-3 |
| spellingShingle | Anish Ghoshal Abhishek Naskar Generalising axion-like particle as the curvaton: sourcing primordial density perturbation and non-Gaussianities European Physical Journal C: Particles and Fields |
| title | Generalising axion-like particle as the curvaton: sourcing primordial density perturbation and non-Gaussianities |
| title_full | Generalising axion-like particle as the curvaton: sourcing primordial density perturbation and non-Gaussianities |
| title_fullStr | Generalising axion-like particle as the curvaton: sourcing primordial density perturbation and non-Gaussianities |
| title_full_unstemmed | Generalising axion-like particle as the curvaton: sourcing primordial density perturbation and non-Gaussianities |
| title_short | Generalising axion-like particle as the curvaton: sourcing primordial density perturbation and non-Gaussianities |
| title_sort | generalising axion like particle as the curvaton sourcing primordial density perturbation and non gaussianities |
| url | https://doi.org/10.1140/epjc/s10052-024-13330-3 |
| work_keys_str_mv | AT anishghoshal generalisingaxionlikeparticleasthecurvatonsourcingprimordialdensityperturbationandnongaussianities AT abhisheknaskar generalisingaxionlikeparticleasthecurvatonsourcingprimordialdensityperturbationandnongaussianities |