When is a right handed neutrino a heavy neutral lepton(HNL)?

[Trixie Mattel]

Hello,

I was just wondering when is a right handed neutrino a heavy neutral lepton?

I know that RH neutrinos show up in a number of extension to the standard model, for example the neutrino minimal standard model (vMSM) and Left-right symmetric extensions.

Ive heard them being referred to as HNL at times and was wondering is it a name that can always be used for RH neutrinos? Or is it only in certain models, or with certain constraints that they can be called heavy neutral leptons?

 

[Orodruin]

I strongly advise that you stop putting the nuMSM at the same level as LR symmetric models. The nuMSM is not a model in the same sense as it is essentially a particular realisation of a type I seesaw where the parameters are chosen in a particular fashion in order to solve a set of SM problems.

Right handed neutrinos are not always heavy. If they are not, they would not be classified as such. However, if they are, they would be heavy neutral fermions.