Improved BBN constraints on Heavy Neutral Leptons. (arXiv:2008.00749v1 [hep-ph])

Improved BBN constraints on Heavy Neutral Leptons. (arXiv:2008.00749v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Boyarsky_A/0/1/0/all/0/1">Alexey Boyarsky</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Ovchynnikov_M/0/1/0/all/0/1">Maksym Ovchynnikov</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Ruchayskiy_O/0/1/0/all/0/1">Oleg Ruchayskiy</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Syvolap_V/0/1/0/all/0/1">Vsevolod Syvolap</a>

We constrain the lifetime of thermally produced Heavy Neutral Leptons (HNLs)
from primordial nucleosynthesis. We show that even a small fraction of mesons
present in the primordial plasma leads to the over-production of the primordial
helium. This puts an upper bound on the lifetime of HNLs $tau_{N}<0.02 s$ for
masses $m_{N}>m_{pi}$ (as compared to 0.1 s reported previously). In
combination with accelerator searches, this allows us to put a new lower bound
on the HNLs masses and defining the “bottom line” for HNL searches at the
future Intensity Frontier experiments.

We constrain the lifetime of thermally produced Heavy Neutral Leptons (HNLs)
from primordial nucleosynthesis. We show that even a small fraction of mesons
present in the primordial plasma leads to the over-production of the primordial
helium. This puts an upper bound on the lifetime of HNLs $tau_{N}<0.02 s$ for
masses $m_{N}>m_{pi}$ (as compared to 0.1 s reported previously). In
combination with accelerator searches, this allows us to put a new lower bound
on the HNLs masses and defining the “bottom line” for HNL searches at the
future Intensity Frontier experiments.

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