Naturally stable right-handed neutrino dark matter

Abstract

Abstract:We point out that a class of non-supersymmetric models based on the gauge group SU(3) C × SU(2) L × SU(2) R × U(1) Y L × U(1) Y R possesses an automatic, exact Z 2 symmetry under which the fermions in the SU(2) R × U(1) Y R sector (called R-sector) are odd and those in the SU(2) L ×U(1) Y L sector (called L-sector or the Standard Model sector) are even. This symmetry, which is different from the usual parity symmetry of the leftright symmetric models, persists in the lepton sector even after the gauge symmetry breaks down to SU(3) C × U(1) EM . This keeps the lightest right-handed neutrino naturally stable, thereby allowing it to play the role of dark matter (DM) in the Universe. There are several differences between the usual left-right models and the model presented here: (i) our model can have two versions, one which has no parity symmetry so that the couplings and masses in the L and R sectors are unrelated, and another which has parity symmetry so that couplings are related but with an extra Higgs doublet in each sector so that the fermion mass patterns are different; (ii) the R-sector fermions are chosen much heavier than the Lsector ones in both scenarios; and finally (iii) both light and heavy neutrinos are Majorana fermions with the light neutrino masses arising from a pure type-II seesaw mechanism. We discuss the DM relic density, direct and indirect detection prospects and associated collider signatures of the model. Comparing with current collider and direct detection constraints, we find a lower bound on the DM mass of order of 1 TeV. We also point out a way to relax the DM unitarity bound in our model for much larger DM masses by an entropy dilution mechanism. An additional feature of the model is that the DM can be made very long lived, if desired, by allowing for weak breaking of the above Z 2 symmetry. Our model also predicts the existence of long-lived colored particles which could be searched for at the LHC.

Scalar dark matter explanation of the DAMPE data in the minimal left-right symmetric model

“…Requiring the existence of right-handed neutrinos in the LRSM, tiny neutrino masses can naturally be generated by the type II seesaw mechanism [8][9][10][11][12]. Besides, the LRSM can accommodate dark matter candidates [13][14][15][16][17][18][19][20][21] and provide a natural framework for baryogenesis through leptogenesis [22]. Its gauge group can naturally appear in the typical SOð10Þ grand unified theory (GUT) group breaking chain [SOð10Þ→ SUð4Þ PS ×SUð2Þ L ×SUð2Þ R →LR], or from the breaking of some other partial unification theories, such as SUð4Þ PS × SUð4Þ W , SUð7Þ, etc.…”

Left-handed and right-handed U(1) gauge symmetry

“…We then have non-trivial chiral structure of neutral gauge boson interactions with the SM fermions taking into account mixing among neutral gauge bosons. Also models with SU(2) L ×SU (2) gauge extension give two extra neutral gauge bosons in which right-handed partner of the SM fermions are introduced [16][17][18]; similar structure is also found in a model in ref. [19] .…”

Prospects of type-II seesaw models at future colliders in light of the DAMPEe+e−excess

“…One could have a fermionic DM instead, and one wellmotivated example is the embedding of type-II seesaw in the left-right framework based on the gauge group SUð3Þ C × SUð2Þ L × SUð2Þ R × Uð1Þ Y L × Uð1Þ Y R [65][66][67], where the lightest right-handed neutrino (RHN) N in the heavy sector is stabilized by an automatic Z 2 symmetry, which is the residual lepton number in the SUð2Þ R sector. In light of the DAMPE data, the RHN DM could annihilate into e þ e − through both the gauge and scalar portals, which, however, are both suppressed by either the small electron mass or the small DM velocity (p-wave mode).…”