What's in the Loop? The Anatomy of Double Higgs Production

TL;DR

The paper addresses how double Higgs production via gluon fusion can illuminate the Higgs self-coupling and the ultraviolet origins of Higgs-gluon interactions. It develops a threshold-based analytic framework for 2h amplitudes with heavy fermion and colored scalar loops, deriving closed-form threshold expressions and exploring heavy-mass limits. Through detailed examples with anomalous Yukawa couplings, fermionic top partners, and scalar top partners, it shows that invariant-mass distributions of hh can distinguish loop spins and mass structures even when total cross sections align with the SM. The work highlights the high-$m_{hh}$ region as a sensitive probe for UV physics at current and future colliders, informing experimental strategies at the HL-LHC and beyond.

Abstract

Determination of Higgs self-interactions through the double Higgs production from gluon fusion is a major goal of current and future collider experiments. We point out this channel could help disentangle and resolve the nature of ultraviolet contributions to Higgs couplings to two gluons. Analytic properties of the double Higgs amplitudes near kinematic threshold are used to study features resulting from scalar and fermionic loop particles mediating the interaction. Focusing on the hh invariant mass spectrum, we consider the effect from anomalous top and bottom Yukawa couplings, as well as from scalar and fermionic loop particles. In particular, the spectrum at high hh invariant mass is sensitive to the spin of the particles in the loop.

Figures (21)

• Figure 1: Top row: Triangle diagrams for $g g \to h h$. Bubble diagrams with quartic scalar-gluon vertices are included with the triangle diagrams in our results. Bottom row: Box diagrams for $g g \to h h$. Triangle diagrams with quartic scalar-gluon vertices are included with the box diagrams.
• Figure 2: Cancellation between contributions to the $2h$ amplitude for fermions (left) or scalars (right) that get their mass entirely through couplings to the Higgs doublet. In the left panel, the value of $\tau_f$ corresponding to the top quark is indicated.
• Figure 3: $2h$ amplitude at threshold in the SM, as a function of the Higgs self-coupling. Only top quarks are included, with $m_t$ = 173 GeV.
• Figure 4: $2h$ amplitude at threshold for scalars that get different contributions to their masses from electroweak symmetry breaking. The left panel shows curves of constant $\kappa/\kappa_0$, while the right panel shows curves of constant physical scalar mass $m_s$.
• Figure 5: $2h$ partonic cross section in the SM, as a function of the Higgs self-coupling. Only top quarks are included, with $m_t$ = 173 GeV.