How long does the hydrogen atom live?

Understand

It is possible that the proton is stable while atomic hydrogen is not.

• This is the case in models with new particles carrying baryon number which are light enough to be stable themselves but heavy enough so that proton decay is kinematically blocked.
• Models of new physics that explain the neutron lifetime anomaly generically have this feature, allowing for atomic hydrogen to decay through electron capture on a proton.
• We calculate the radiative hydrogen decay rate involving the emission of a few hundred keV photon, which makes this process detectable in experiment.