Higgs Underproduction at the LHC

TL;DR

The paper investigates how new colored scalars coupled to the Higgs via Higgs portal interactions can destructively interfere with the Standard Model top-quark loop, substantially suppressing Higgs production through gluon fusion. Focusing on a color-octet real scalar, it derives the modified gg→h amplitude and identifies parameter regions (negative κ and relatively light scalar masses) where suppression can exceed an order of magnitude without severely impacting Higgs decays. It also analyzes experimental constraints, noting that ATLAS excludes certain low-mass color-octet scenarios while larger regions remain viable, and discusses collider signatures from pair-produced colored scalars leading to multi-jet final states. The results imply that the Higgs could exist across a broad mass range consistent with LHC limits, provided new colored states exist that modify production rates, thereby motivating revised Higgs-search strategies and complementary probes such as di-Higgs production and VBF/associated channels.

Abstract

We show that production of the Higgs boson through gluon-fusion may be suppressed in the presence of colored scalars. Substantial destructive interference between the top quark diagrams and colored scalar diagrams is possible due to cancellations between the real (and also imaginary) parts of the amplitudes. As an example, we consider a color-octet scalar that has a negative, order one coupling to the Higgs doublet. We find that gluon fusion can be suppressed by more than an order of magnitude when the scalar mass is below a few hundred GeV, while milder suppressions occur for larger scalar masses or smaller couplings. Thus, the standard model extended with only one particle can evade the full range of present LHC exclusion limits on the Higgs mass. The colored scalars, however, would be produced in pairs with a large rate at the LHC, leading to multi-jet final states to which the LHC experiments are now becoming sensitive.

Figures (5)

• Figure 1: Feynman diagrams for scalar loop contributions to $gg \rightarrow h$. A real scalar field has precisely these diagrams, while a complex field also has a third diagram that can be obtained from the second diagram by swapping the initial state gluons.
• Figure 2: Contours of the Higgs production cross section through gluon fusion at leading order, including the effects of a color-octet real scalar having Higgs portal coupling $\kappa$ and mass $M_\Theta$, normalized to the standard model value. The inner (red), middle (blue), outer (green) regions correspond to $\sigma(pp\rightarrow h)/\sigma(pp\rightarrow h)_{SM} < 0.1, 0.25, 0.5$ respectively. The top, middle, and bottom panels show increasing Higgs mass. As thresholds for $h \rightarrow 2$-body decays are crossed, qualitative changes in the suppression of the Higgs production through gluon fusion are evident.
• Figure 3: Contours of the Higgs production cross section through gluon fusion at leading order, including the effects of a color-octet real scalar, normalized to the standard model value. Unlike Fig. \ref{['fig:matching']}, we have fixed the Higgs portal coupling to $\kappa = -0.6, -1.2$ in the upper and lower plots, respectively, while allowing $M_h$ and $M_\Theta$ to vary.
• Figure 4: Cross section $\sigma(pp \rightarrow h)$ relative to the standard model value for octets of mass $125\,\text{GeV}$ (dotted line), $175\,\text{GeV}$ (small dashes) and $250\,\text{GeV}$ (large dashes) and Higgs portal coupling $\kappa = -0.75$.
• Figure 5: Limit on the production cross section for a pair of dijet resonances from ATLAS Aad:2011yh (solid line), and the leading-order theoretical cross section (dashed line) for pair production of a color-octet real scalar at the 7 TeV LHC.