Type III Neutrino Seesaw, Freeze-In Long-Lived Dark Matter, and the $W$ Mass Shift

Abstract

In the framework of seesaw neutrino masses from heavy fermion triplets $({\Sigma }^{+},{\Sigma }^0,{\Sigma }^{-})$, the addition of a light fermion singlet $N$ and a heavy scalar triplet $({\rho }^{+},{\rho }^0,{\rho }^{-})$ has some important consequences. The new particles are assumed to be odd under a new $Z_2$ symmetry which is only broken softly, both explicitly and spontaneously. With $N-{\Sigma }^0$ mixing, freeze-in long-lived dark matter through Higgs decay becomes possible. At the same time, the $W$ mass is shifted slightly upward, as suggested by a recent precision measurement.

Comments: 6 pages, 2 figures, typos corrected