A Very Heavy Sneutrino as Viable Thermal Dark Matter Candidate in $U(1{)}^{\prime }$ Extensions of the MSSM

Abstract

We study the Standard Model singlet ("right-handed") sneutrino ${\tilde{\nu }}_R$ dark matter in a class of $U(1{)}^{\prime }$ extensions of the MSSM that originate from the breaking of the $E_6$ gauge group. These models, which are referred to as UMSSM, contain three right--handed neutrino superfields plus an extra gauge boson $Z^{\prime }$ and an additional SM singlet Higgs with mass $\simeq M_{Z^{\prime }}$, together with their superpartners. In the UMSSM the right sneutrino is charged under the extra $U(1{)}^{\prime }$ gauge symmetry; it can therefore annihilate via gauge interactions. In particular, for $M_{{\tilde{\nu }}_R}\simeq M_{Z^{\prime }}/2$ the sneutrinos can annihilate by the exchange of (nearly) on--shell gauge or Higgs bosons. We focus on this region of parameter space. For some charge assignment we find viable thermal ${\tilde{\nu }}_R$ dark matter for mass up to $\sim 43$ TeV. This is the highest mass of a good thermal dark matter candidate in standard cosmology that has so far been found in an explicit model. Our result can also be applied to other models of spin$-0$ dark matter candidates annihilating through the resonant exchange of a scalar particle. These models cannot be tested at the LHC, nor in present or near--future direct detection experiments, but could lead to visible indirect detection signals in future Cherenkov telescopes.

Comments: 29 pages, 6 figures, 1 table