I have been betting against the fourth type of neutrino. You don’t have to be a seer to make this prediction because there is overwhelming evidence against the existence of the fourth generation of fermions. Now, there is more experimental evidence that eliminates a large portion of the remaining parameter space in which a fourth type of neutrino could exist.
Other ways of saying that there is no fourth generation of fermions
- fourth type of neutrino does not exist
- sterile neutrino does not exist
- right-handed neutrino does not exist
I have been betting against the fourth type of neutrino. See these posts
Final reports from the Planck Cosmic Background Radiation Measurements
Planck results prove without any doubt that there are only 3 types of neutrinos. This is very important because this also proves that there are only 3 generations of fermions. Some theorists desperately seek the so-called sterile neutrino (4’th type of neutrino which would be heavy and right-chiral) but I don’t understand their motivation because the precision experiments at CERN in the 90’s (LEP experiments Aleph, Delphi, L3, Opal) also proved that there are only 3 types of neutrinos.
Fourth type of neutrino has never been observed
The results from the LEP experiments at CERN in the 90’s also indicate that there are only 3 types of neutrinos. Precise measurements of the Z-boson (one of the force-carrying particles of the electroweak force) properties in the CERN LEP experiments (Aleph, Delphi, L3, and Opal) provided clear evidence that the number of fermion generations is 3. Since neutrinos are also fermions (spin=1/2 particles) LEP results strongly suggest that there are only 3 types of neutrinos.
Sterile Neutrino Down but Not Completely Out
“Now the collaborations behind the MINOS and MINOS+ experiments at Fermilab in the US and the Daya Bay Reactor Neutrino Experiment in China have released an analysis that eliminates a large portion of the remaining parameter space in which sterile neutrinos could exist . But the teams have not yet studied all their data, and other experiments do see possible signals, leaving the door ajar for the existence of this disputed particle.”
“These new constraints exacerbate tension surrounding the sterile neutrino. This tension comes because they exclude mass splittings values for sterile neutrino signals that could explain both the early LSND and MiniBooNE experiments and also in new unpublished MiniBooNE experiments that analyze a 17-year-long dataset. Other unpublished results, this time from the IceCube Collaboration, which analyzes eight years of atmospheric muon neutrino data, also question the existence of a sterile neutrino. And the absence of a sterile neutrino fits with data from the Planck satellites that measure the energy density of the early Universe”.
 P. Adamson et al. (MINOS+ and Daya Bay Collaborations), “Improved constraints on sterile neutrino mixing from disappearance searches in the MINOS, MINOS+, Daya Bay, and Bugey-3 experiments,” Phys. Rev. Lett. 125, 071801 (2020).