# I Seesaw Mechanism of vMSM and Left Right Symmetric Extension

1. Mar 15, 2017

### Trixie Mattel

I know the seesaw mechanism is a model used to explain both neutrinos having mass and why their dirac mass/yukawa coupling is so much smaller than for the other fermions.

The seesaw mechanism needs the right handed neutrino to exist. How does the seesaw mechanism for the vMSM differ from that of a Left Right Symmetric extension of the standard model considering that in the vMSM the right handed neutrino is a singlet (for SU(2)) whereas in LR symmetric extensions the right handed neutrino is in a doublet with its corresponding flavour lepton

Also does a difference in the two mechanisms lie in the fact that the Higgs is a doublet in vMSM and a multiplet in a Left Right symmetric extension?

Thank you

Last edited: Mar 15, 2017
2. Mar 15, 2017

### ChrisVer

Hmmm... I don't think that the see-saw mechanism predicts new particles apart from the possible extra Higgs' ? While LR models predict the existence of new gauge bosons ($W'_R, Z'_R$)?

3. Mar 15, 2017

### Orodruin

Staff Emeritus
This depends on which type of seesaw you are considering. In the type-II seesaw there is a doublet scalar and no right-handed neutrinos and in the type-III there are SU(2) triplet fermions.

After the LR symmetry breaking - not at all. Apart from that the nuMSM is a particular implementation that needs particular parameter combinations to be realised.

See above. Type-I: Extra fermion singlets (sterile neutrinos/right-handed neutrinos). Type-II: Triplet scalar. Type-III: Triplet fermions. There is no need for extra higgses (unless in the type-II if you count any scalar as a higgs).