Color-octet scalars at the LHC

TL;DR

The paper analyzes color-octet scalars in the representation $$(8,2)_{1/2}$$ that couple to quarks under minimal flavor violation. RG running and Tevatron constraints strongly disfavor two-body gauge-boson decays, steering decays toward heavy fermion pairs and making pair production the most promising discovery channel at the LHC. Through detailed collider studies, it shows that neutral and charged $S$-pairs can yield robust signals in $t\bar t t\bar t$, $b\bar b b\bar b$, and $b\bar b t\bar t$ final states, with discovery potential for masses well above 1 TeV, using boosted-top jet reconstruction. The work also discusses potential probes of $S$–Higgs couplings via exotic Higgs decays or associated production, though such signatures face significant experimental challenges. Overall, the paper argues that MFV color-octet scalars are testable at the LHC, primarily through heavy-quark rich final states, provided careful top-tagging and background control are employed.

Abstract

Color-octet scalars, if present at the TeV scale, will be produced in abundance at the LHC. We discuss in some detail the phenomenology of scalars in the (8,2)_{1/2} representation, recently identified by Manohar and Wise as an addition to the standard-model Higgs sector consistent with the principle of minimal flavor violation. Couplings of this multiplet to the Higgs lift the mass degeneracy among its states, possibly allowing for two-body decays of a heavier colored scalar to a lighter one and a gauge boson. We perform a renormalization group analysis of these couplings and find that limits from Tevatron searches leave little room for these decays. This fact, and the assumption of minimal flavor violation, lead us to study the case where the octets decay to the heaviest kinematically accessible fermion pairs. Focusing on pair-production events leading to (t t-bar t t-bar), (b b-bar b b-bar), and (b b-bar t t-bar) final states, we find that discovery at the LHC should be possible up to masses exceeding 1 TeV.

Figures (6)

• Figure 1: The minimum value of $|\lambda_2 \pm 2\lambda_3|$ that allows for two-body decays involving $W^+$. The positive sign corresponds to $S^R \to W^+ S^-$ or $S^- \to W^- S^R$, and negative corresponds to $S^I \to W^+ S^-$ or $S^- \to W^- S^I$.
• Figure 2: The minimum value of $|\lambda_3|$ that allows for $S^I \to Z S^R$ or $S^R \to Z S^I$.
• Figure 3: Invariant mass distributions from reconstructed top quark pairs, for signal and $t{\overline t}$ background. The signal is stacked on the background. Looking in the mass window $1 \pm 0.1$ TeV gives a signal significance of over 5$\sigma$.
• Figure 4: Invariant-mass distribution for pairs of b-tagged jets, for the case where the neutral $S$ states decay dominantly to $b {\overline b}$.
• Figure 5: Invariant mass distributions from $b$-jet -- reconstructed top quark pairs, for charged-octet signal and $t{\overline t}$ background. The signal is stacked on the background. Looking in the mass window $1 \pm 0.1$ TeV gives a signal significance of over 5$\sigma$.