Enhanced di-Higgs Production through Light Colored Scalars

TL;DR

This paper shows that introducing light colored scalars with Higgs portal couplings can dramatically boost di-Higgs production at the LHC, potentially by up to three orders of magnitude relative to the SM, for mh ≈ 125 GeV, or by substantial factors if mh is heavier. The authors develop both an EFT framework and a full one-loop calculation to capture momentum-dependent effects, using a real color-octet scalar as a benchmark. They find that negative Higgs-portal couplings κ and relatively light scalar masses M_S maximize the enhancement, with distinctive correlations between single- and di-Higgs rates and observable signals in γγbb, ττbb, and multi-boson final states. The work emphasizes the importance of momentum dependence and proposes concrete collider strategies, including jet-substructure techniques, to discover or constrain enhanced di-Higgs production. If validated, these enhancements offer a compelling avenue to probe new colored states and the Higgs sector at the LHC.

Abstract

We demonstrate enhanced di-Higgs production at the LHC in the presence of modifications of the effective couplings of Higgs to gluons from new, light, colored scalars. While our results apply to an arbitrary set of colored scalars, we illustrate the effects with a real color octet scalar -- a simple, experimentally viable model involving a light (~125-300 GeV) colored scalar. Given the recent LHC results, we consider two distinct scenarios: First, if the Higgs is indeed near 125 GeV, we show that the di-Higgs cross section could be up to nearly one thousand times the Standard Model rate for particular octet couplings and masses. This is potentially observable in \emph{single} Higgs production modes, such as $pp \to h h \to γγb\bar{b}$ as well as $pp \to h h \to τ^+τ^- b\bar{b}$ where a small fraction of the $γγ$ or $τ^+τ^-$ events near the putative Higgs invariant mass peak contain also a $b\bar{b}$ resonance consistent with the Higgs mass. Second, if the Higgs is not at 125 GeV (and what the LHC has observed is an impostor), we show that the same parameter region where singly-produced Higgs production can be suppressed below current LHC limits, for a heavier Higgs mass, also simultaneously predicts substantially enhanced di-Higgs production. We point out several characteristic signals of di-Higgs production with a heavier Higgs boson, such as $pp \to hh \to W^+W^-W^+W^-$, which could use same-sign dileptons or trileptons plus missing energy to uncover evidence.

Figures (8)

• Figure 1: Effective operator contributions to $gg \rightarrow hh$.
• Figure 2: Scalar loop contributions to $gg \rightarrow hh$. The three diagrams on left are $\mathcal{O}(\alpha_s \kappa)$, while the four diagrams on the right are $\mathcal{O}(\alpha_s \kappa^2)$, where $\kappa$ is the Higgs-portal coupling.
• Figure 3: Di-Higgs as well as single Higgs production cross sections normalized to the Standard Model values. The solid lines show $\sigma(pp \rightarrow hh)_{\rm scalar+top}/\sigma(pp \rightarrow hh)_{\rm top}$, while the colored regions show when $\sigma(pp \rightarrow h)_{\rm scalar+top}/\sigma(pp \rightarrow h)_{\rm top}$ is less than the numerical value labeling each region. Panels (b) and (c) are "zoomed in" versions of panel (a), to more clearly see the contours in the light $M_S < 200$ GeV region.
• Figure 4: Same as Fig. \ref{['fig:125']}, but for heavier Higgs masses (assuming the $125$ GeV particle observed by LHC is an imposter). The viable parameter space is roughly in the red and blue regions where $\sigma(pp \rightarrow h)_{\rm scalar + top}/\sigma(pp \rightarrow h)_{\rm top} \mathrel{\hbox{$<$$\sim$}} 0.25$. Whenever $m_h > 2\, M_S, 2\, m_t$ there is little space for a suppressed $\sigma(pp \rightarrow h)$. This occurs because the loop contributions to the amplitude become complex, and cancellation must be arranged simultaneously between the real and imaginary parts of the top quark and scalar loops.
• Figure 5: Kinematic distributions for the $p_{T,h}$ of the Higgs boson in di-Higgs production at LHC. Panel (a) shows $(1/\sigma) d\sigma(gg \rightarrow hh)/dp_{T,h}$ for the SM alone (red) and the SM combined with loops of scalars, $M_S = 160\,\text{GeV}$ (green), $M_S = 200\,\text{GeV}$ (orange), $M_S = 250\,\text{GeV}$ (gray) and $M_S = 300\,\text{GeV}$ (cyan). The Higgs-portal has been taken to be $\kappa = -1$ for all cases. The right panel shows the Higgs rapidity distribution $(1/\sigma) d\sigma(gg \rightarrow hh)/d Y_{h}$ for the same scalar values.