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تسجيل مستخدم جديدSolving the Hubble tension without spoiling Big Bang Nucleosynthesis
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The Hubble parameter inferred from cosmic microwave background observations is consistently lower than that from local measurements, which could hint towards new physics. Solutions to the Hubble tension typically require a sizable amount of extra radiation $Delta N^{}_{rm eff}$ during recombination. However, the amount of $Delta N^{}_{rm eff}$ in the early Universe is unavoidably constrained by Big Bang Nucleosynthesis (BBN), which causes problems for such solutions. We present a possibility to evade this problem by introducing neutrino self-interactions via a simple Majoron-like coupling. The scalar is slightly heavier than $1~{rm MeV}$ and allowed to be fully thermalized throughout the BBN era. The rise of neutrino temperature due to the entropy transfer via $phi to uoverline{ u}$ reactions compensates the effect of a large $Delta N^{}_{rm eff}$ on BBN. Values of $Delta N^{}_{rm eff}$ as large as $0.7$ are in this case compatible with BBN. We perform a fit to the parameter space of the model.
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