Gravitational Interactions and Neutrino Masses
  We describe a scenario where the smallness of neutrino masses is related to a
global symmetry that is only violated by quantum gravitational effects. The
coupling of neutrinos to gauge singlet right-handed fermions is attributed to
symmetry preserving gravitational operators suppressed by the Planck mass, in
this framework. The proposed scenario leads to axion particles that decay into
neutrinos, which could be probed through cosmological measurements and may help
explain the Hubble parameter tension. Depending on the details of the
implementation, the scenario could provide axion dark matter candidates.
