  We consider the production of a new MeV-scale fermion in coherent elastic
neutrino-nucleus scattering. The effect on the measurable nucleon recoil
spectrum is calculated. Assuming that the new fermion couples to neutrinos and
quarks via a singlet scalar, we set limits on its mass and coupling using
COHERENT data and also determine the sensitivity of the CONUS experiment. We
investigate the possible connection of the new fermion to neutrino mass
generation. The possibility of the new fermion being the dark matter particle
is also studied.
