content_image/372556.jpg content_image/372554.jpg content_image/372553.jpg
by the point: 

<img src='content_image/372556.jpg'>

where m$_{0}$ is the universal scalar mass, m$_{1}$$_{/}$$_{2}$ is the universal gaugino mass, A$_{0}$ is the common trilinear coupling, tan β is the ratio of the Higgs VEVs, and µ is the Higgsino mass parameter, all of which are evaluated at M$_{GUT}$ ∼ 10 16 GeV and run down with the renormalization group equations to determine all the low-scale parameters of the theory. A feature of this benchmark point is that the gluino mass, m$_{˜}$ g = 782 GeV, is less that that of the squarks. Gluino decays to quark-squark pairs (˜ g → q ¯ ˜ q$_{L,R}$, ¯ q ˜ q$_{L,R}$ ) are kinematically inaccessible, opening up three-body decays via virtual squarks: 

<img src='content_image/372554.jpg'>

These decays can result in both single- and double-top final states with considerable branch- ing fractions of ≈ 10% − 20% when summing over all neutralinos and charginos, an enhance- ment that has been studied for similar regions of parameter space [12–14]. These branching fractions are given in Table II. 

Because gluinos are strongly interacting, the production of gluino pairs at the LHC will be very large, typically several hundred fb. With one gluino decaying to a single top via ˜ g → t ¯ bχ − i or ¯ tbχ + i and the other to a top pair through ˜ g → χ 0 $_{i}$t ¯ t , the rate of triple-top events can therefore be quite large in the MSSM in this region of parameter space. The diagram for the leading contribution is given in Figure 3. 

The major limitations to the rate of triple-top production in the SM, as discussed in Section II, are the W tb vertex and the initial state b -quark needed to create the single top (though the latter is not involved for pp → tt ¯ t b ). Models that can produce this single top with greater ease should therefore have a larger triple-top signal as well. An example of one such model is the addition of a U (1) ′ symmetry in which a leptophobic Z ′ couples the top directly to the u -quark. The additional interaction terms of the Lagrangian are given by 

<img src='content_image/372553.jpg'>

