Abstract
Curvatons are light (compared to the Hubble scale during inflation) spectator fields during inflation that potentially contribute to adiabatic curvature perturbations post-inflation. They can alter CMB observables such as the spectral index ns, the tensor-to-scalar ratio r, and the local non-Gaussianity \( {f}_{\textrm{NL}}^{\left(\textrm{loc}\right)} \). We systematically explore the observable space of a curvaton with a quadratic potential. We find that when the underlying inflation model does not satisfy the ns and r observational constraints but can be made viable with a significant contribution from what we call a savior curvaton, a large \( \left|{f}_{\textrm{NL}}^{\left(\textrm{loc}\right)}\right| \) > 0.05, such that the model is distinguishable from single-field inflation, is inevitable. On the other hand, when the underlying inflation model already satisfies the ns and r observational constraints, so significant curvaton contribution is forbidden, a large \( \left|{f}_{\textrm{NL}}^{\left(\textrm{loc}\right)}\right| \) > 0.05 is possible in the exceptional case when the isocurvature fluctuation in the curvaton fluid is much greater than the global curvature fluctuation.
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Acknowledgments
JL and QL would like to thank Matt Reece for helpful discussions and for feedback on previous drafts of this work. QL is grateful to Rashmish Mishra for useful discussions. JL would like to thank Daniel Green for his comments on future observational prospects of cosmological observables mentioned in this work. The work of QL is supported by the DOE grant DE-SC0013607, the Alfred P. Sloan Foundation Grant No. G-2019-12504, and the NASA Grant 80NSSC20K0506. The work of LR is supported by NSF grants PHY-1620806 and PHY-1915071, the Chau Foundation HS Chau postdoc award, the Kavli Foundation grant “Kavli Dream Team,” and the Moore Foundation Award 8342. The work of JL is supported by the Moore Foundation Award 8342 and Harvard University institutional funding.
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Lodman, J., Lu, Q. & Randall, L. Savior curvatons and large non-Gaussianity. J. High Energ. Phys. 2023, 218 (2023). https://doi.org/10.1007/JHEP11(2023)218
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DOI: https://doi.org/10.1007/JHEP11(2023)218