Double seesaw mechanism in a left-right symmetric model with TeV neutrinos

A left-right symmetric model is discussed with new mirror fermions and a Higgs sector with two doublets and neutral scalar singlets. The seesaw mechanism is generalized, including not only neutrino masses but also charged fermion masses. The spectrum of heavy neutrinos presents a second seesaw mass matrix and has neutrinos masses naturally in the TeV region. The model has very clear signatures for the new neutral vector gauge bosons. Two classes of models are discussed. New mirror neutrinos can be very light and a new ${Z}^{\ensuremath{'}}$ can be discriminated from other models by a very high invisible branching fraction. The other possibility is that mirror neutrinos can have masses naturally in the TeV region and can be produced through ${Z}^{\ensuremath{'}}$ decays into heavy neutrino pairs. Signatures and production processes for the model at the LHC energy are also presented.