Dark matter and collider signals in an MSSM extension with vector-like multiplets

Motivated by grand unification considerations, we analyse a simple extension of the minimal supersymmetric standard model with additional pairs of vector-like chiral supermultiplets. We focus on the so-called LND setup, which enlarges the particle content of the minimal model by two vector-like pairs of weak doublets (one pair of leptons and one pair of down-type quarks) and one vector-like pair of neutrino singlets. Imposing collider and low-energy constraints, sneutrinos and neutralinos both emerge as possible lightest supersymmetric particles and thus dark matter candidates. We perform a complete analysis of the dark sector and study the viability of these neutralino and sneutrino dark matter options. We show that cosmological considerations (the dark matter relic abundance and its direct and indirect detection signals) restrict neutralino dark matter to exhibit similar properties as in the minimal supersymmetric standard model, and impose the sneutrino dark matter candidate to be singlet-like, rather than doublet-like. Allowing the mixing of the fermionic component of the new supermultiplets with the Standard Model third generation fermions, we moreover demonstrate the existence of collider signals that are distinguishable from other, more minimal, supersymmetric scenarios by virtue of an enhanced production of events enriched in tau leptons. We furthermore show that this signature yields robust LHC signals, that could potentially be differentiated from the background in future data.

Figure 1

Representative dark matter annihilation diagram into vector-like fermions.

Figure 2

Relic abundance of neutralino dark matter in the LND model as a function of the dark matter mass, with all known funnels and coannihilation channels (left) or without those channels (right). The different colors correspond to the relative importance of the contributions from annihilations into vector-like fermions to the total dark matter annihilation cross section (blue to red for increasing contribution). The horizontal dashed lines indicate the region favored by Planck data [54].

Figure 3

Sneutrino relic abundance as a function of its mass. In the left panel we highlight in blue the parameter space points for which the lightest sneutrino is dominated by a doublet component, whereas red points are essentially singlet-like. In the right panel, we indicate which of the parameter space points are characterized by large (red) or small (blue) mass splittings between the lightest sneutrino and the NLSP.

Figure 4

Direct (left panel) and indirect (right panel) detection constraints on sneutrino dark matter in the LND model as a function of the dark matter mass. In both cases we highlight, in darker blue, the parameter space points for which the two-sided Planck constraint can be satisfied.

Figure 5

Distributions in the $H_T$, $M_{\mathrm{eff}}$ and $M_{4\ell }$ observables for the $\mathbf{BP}\mathbf{1}$ benchmark scenario and the dominant contributions to the SM background, once the preselection cuts of Eq. (5.3) have been imposed. The normalization is arbitrary.