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Increasing the effective number of neutrinos with decaying particles

Kazuhide Ichikawa·Masahiro Kawasaki·Kazunori Nakayama·Masato Senami·Fuminobu Takahashi
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Abstract

We present models of decaying particles for increasing the effective number of neutrinos N_nu after big bang nucleosynthesis but before the structure formation begins. We point out that our scenario not only solves the discrepancy between the constraints on N_nu from these two epochs, but also provides a possible answer to deeper inconsistency in the estimation of the matter power spectrum amplitude at small scales, represented by sigma_8, between the WMAP and some small scale matter power measurements such as the Lyman-alpha forest and weak lensing. We consider (a) saxion decay into two axions; (b) gravitino decay into axino and axion; (c) Dirac right-handed sneutrino decay into gravitino and right-handed neutrino.

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Kazuhide Ichikawa, Masahiro Kawasaki, Kazunori Nakayama, Masato Senami, Fuminobu Takahashi. 2007-05-12. Increasing the effective number of neutrinos with decaying particles. https://doi.org/10.1088/1475-7516%2F2007%2F05%2F008

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