Color Octet Scalar Production at the LHC

TL;DR

The paper addresses the potential collider phenomenology of color octet scalars under minimal flavor violation (MFV), focusing on a single neutral octet scalar produced via gluon fusion. It derives an experimental constraint on the up-type Yukawa coupling η_U from precision electroweak data (R_b) and provides explicit formulas for the one-loop gg→S^0 production rates, showing that single production can surpass tree-level pair production at TeV-scale masses. The work demonstrates how MFV shapes the viable parameter space and identifies the LHC energy regime where loop-induced single production of color octet scalars is most impactful. These results inform searches for TeV-scale color octet resonances and guide interpretation of future collider data.

Abstract

New physics at the weak scale that can couple to quarks typically gives rise to unacceptably large flavor changing neutral currents. An attractive way to avoid this problem is to impose the principal of minimal flavor violation (MFV). Recently it was noted that in MFV only scalars with the same gauge quantum numbers as the standard model Higgs doublet or color octet scalars with the same weak quantum numbers as the Higgs doublet can couple to quarks. In this paper we compute the one-loop rate for production of a single color octet scalar through gluon fusion at the LHC, which can become greater than the tree level pair production rate for octet scalar masses around a TeV. We also calculate the precision electroweak constraint from Z decays to a b and anti-b quark; this constraint on color octet mass and Yukawa coupling affects the allowed range for single octet scalar production through gluon fusion.

Figures (5)

• Figure 1: Feynman diagrams contributing to $Z b \bar{b}$ vertex correction.
• Figure 2: One (solid line) and two (dashed line) standard deviation exclusion contours due to $R_b$. (Parameter space above these lines is excluded.) The curves were calculated using $m_t = 170.9$ GeV, $\sin^2 \theta_{\text{eff, lept}} = 0.23153$, $m_Z = 91.1876$ GeV, and $v = 246$ GeV.
• Figure 3: Diagrams contributing to $S^0_R$ production via gluon fusion. For real $\lambda_{4,5}$, only the top loop contributes to $S^0_I$ production.
• Figure 4: Production cross sections (in femto-barns) at LHC center of mass energy $\sqrt{s} = 14$ TeV for two real neutral scalars (solid line: $pp \rightarrow S^0_{R(I)} S^0_{R(I)} X$), one real neutral scalar (long dash: $pp \rightarrow S^0_{R} X$), and one real neutral pseudoscalar (short red dash: $pp \rightarrow S^0_{I} X$). The single color octet production cross sections are plotted with $\eta_U = 1$ and include only the top loop contribution, as the scalar loop contributions are negligible for $\lambda_{4, 5} \sim 1$. We used CTEQ5 next-to-leading order parton distribution functions cteq, and we used the two-loop $\beta$ function to run $\alpha_s(m_Z) = 0.1216$ up to $\alpha_s(2 m_S)$ for scalar pair production and $\alpha_s(m_S)$ for single scalar production. The curves were calculated using $m_t = 170.9$ GeV.
• Figure 5: Production cross sections (in femto-barns) at Tevaton center of mass energy $\sqrt{s} = 1.96$ TeV for one real neutral scalar (solid line: $p \bar{p} \rightarrow S^0_{R} X$), and one real neutral pseudoscalar (dashed line: $p \bar{p} \rightarrow S^0_{I} X$). For this plot, $\eta_U = 1$ and the $\lambda_{4,5}$ terms in \ref{['decayrate']} are neglected. We used CTEQ5 next-to-leading order parton distribution functions cteq, and we used the two-loop $\beta$ function to run $\alpha_s(m_Z) = 0.1216$ up to $\alpha_s(m_S)$. The curves were calculated using $m_t = 170.9$ GeV.