Color-Octet Scalars of N=2 Supersymmetry at the LHC

TL;DR

This work examines color-octet scalars (sgluons) in an $N=1/N=2$ hybrid SUSY framework, predicting large $gg$ and $q\bar{q}$–initiated pair production of $\sigma$ at the LHC and distinctive decay cascades. The $\sigma$ field, a color-octet complex scalar, couples to gluinos and squarks with a Dirac gluino structure, yielding tree-level decays to gluino/squark pairs and loop-induced decays to $gg$ or $t\bar{t}$; single production arises at one loop and is suppressed unless squark masses are nondegenerate. Phenomenologically, $\sigma$ pair production leads to spectacular final states, notably eight jets plus four LSPs, or four tops if kinematically allowed, with loop-induced decays providing additional resonant signatures. The study also notes that introducing the N=2 sector alters one-loop running of gauge couplings, removing simple unification, though this has limited impact on the low-energy, collider-focused analysis. Overall, the color-octet scalar sector offers distinctive LHC signatures that differ from the MSSM, motivating targeted searches for high-multiplicity jet events and potential top-quark-rich final states.

Abstract

The color gauge hyper-multiplet in N=2 supersymmetry consists of the usual N=1 gauge vector/gaugino super-multiplet, joined with a novel gaugino/scalar super-multiplet. Large cross sections are predicted for the production of pairs of the color-octet scalars $σ$ [sgluons] at the LHC: $gg, q\bar{q} \to σσ^{\ast}$. Single $σ$ production is possible at one-loop level, but the $g g\to σ$ amplitude vanishes in the limit of degenerate $L$ and $R$ squarks. When kinematically allowed, $σ$ decays predominantly into two gluinos, whose cascade decays give rise to a burst of eight or more jets together with four LSP's as signature for $σ$ pair events at the LHC. $σ$ can also decay into a squark-antisquark pair at tree level. At one-loop level $σ$ decays into gluons or a $t \bar t$ pair are predicted, generating exciting resonance signatures in the final states. The corresponding partial widths are very roughly comparable to that for three body final states mediated by one virtual squark at tree level.

Figures (5)

• Figure 1: Diagrams for (a) the effective $\sigma gg$ vertex built up by squark loops; (b) the effective $\sigma q\bar{q}$ vertex with $L$ squarks and gluinos -- the coupling to $R$ squarks being mediated by the charge-conjugate Dirac gluinos.
• Figure 2: Branching ratios for $\sigma$ decays, for $m_{\tilde{q}_L} = 2 m_{\tilde{g}} = 1$ TeV (Left) and $m_{\tilde{g}} = 2 m_{\tilde{q}_L} = 1$ TeV (Right). In both cases we assumed a neutralino mass $m_{\tilde{\chi}} = 0.16 m_{\tilde{g}}$, and moderate squark mass splitting: $m_{\tilde{q}_R} = 0.95 m_{\tilde{q}_L}, \, m_{\tilde{t}_L} = 0.9 m_{\tilde{q}_L},\, m_{\tilde{t}_R} = 0.8 m_{\tilde{q}_L}$, with $\tilde{t}_L$-$\tilde{t}_R$ mixing determined by $X_t = m_{\tilde{q}_L}$.
• Figure 3: Feynman diagrams for sigma-pair production in quark annihilation (a) and gluon fusion (b).
• Figure 4: Parton cross sections for $\sigma\sigma^\ast$ production in the $q\bar{q}$ (Left) and $gg$ (Right) channel. For comparison, the production of 3rd generation squark pairs is shown by the dashed lines for the same masses.
• Figure 5: Cross sections for $\sigma$-pair [and $\tilde{q}_3$-pair] production (red lines), as well as for single $\sigma$ production (blue lines), at the LHC. In the latter case the solid blue curve has been obtained using the same mass parameters as in Fig.2 (Right), while the dashed blue curve adopts the mSUGRA benchmark point SPS1a$'$.