Freeze-in sterile neutrino dark matter in a feebly gauged B − L model
摘要
We consider the gauged U(1)B−L model and examine the situation where the sterile neutrino is a dark matter candidate produced by the freeze-in mechanism. In our model, the dark matter N is mainly produced by the decay of a U(1)B−L breaking scalar boson ϕ. We point out that the on-shell production of ϕ through annihilation of the U(1)B−L gauge boson Z′ plays an important role. We find that the single production of Z′ from the gluon bath in the early Universe can become the main production modes for Z′ in some parameter regions. To prevent N from being overproduced, we show that the U(1)B−L gauge coupling constant gB−L must be as small as 10−16–10−10. We also consider the case where the decay of ϕ into N is kinematically forbidden. In this case, N is generated by the scattering of Z′ and the gB−L takes values of 10−10–10−6, which can be explored in collider experiments like FASER and SHiP.