Neutron lifetime and dark decay of the neutron and hydrogen

Understand

The neutron, besides its $\beta$-decay $n\to p e\bar\nu_e$, might have a new decay channel $n\to n' X$ into mirror neutron $n'$, its nearly mass degenerate twin from parallel dark sector, and a massless boson $X$ which can be ordinary and mirror photons or some more exotic particle.

• Such an invisible decay could alleviate the tension between the neutron lifetimes measured in the beam and trap experiments.
• I discuss some phenomenological and astrophysical consequences of this scenario, which depends on the mass range of mirror neutron $n'$.
• Namely, the case $m_{n'} < m_p + m_e$ leads to a striking possibility is that the hydrogen atom $^1$H (protium), constituting 75 per cent of the baryon mass in the Universe, could in fact be unstable: it can decay via the electron capture into $n'$ and $\nu_e$, with relatively short lifetime $\sim 10^{21}$ yr or so.