Two-loop BSM contributions to Higgs pair production in the aligned THDM

TL;DR

The paper tackles the challenge of precise Higgs-pair production predictions in the aligned THDM when BSM quartic couplings are large. It advances the theory by recomputing the two-loop corrections to the SM-like Higgs trilinear λ_{hhh}, computing the first full two-loop corrections to λ_{hhH}, and including relevant two-loop Higgs–gluon and s-channel propagator corrections, all within a renormalization framework that preserves alignment beyond tree level. The authors find that two-loop BSM corrections to λ_{hhh} can be as large as the one-loop contributions, and that λ_{hhH} receives non-negligible two-loop effects; the NNLO cross section is largely controlled by λ_{hhh} corrections, with subdominant terms contributing up to about 10–20% depending on the scenario. A key message is the strong dependence of the results on the renormalization prescription for the parameter M^2, illustrating the sensitivity of BSM scenarios with large couplings and motivating further refinements including NNLO QCD matching and parameter-space scans.

Abstract

We study the impact of the two-loop corrections controlled by the BSM Higgs couplings on the cross section for the production of a pair of SM-like Higgs bosons via gluon fusion in the aligned THDM. To this aim, we reassess the two-loop calculation of $λ_{hhh}$, we compute for the first time the two-loop corrections to $λ_{hhH}$, and we include the relevant corrections to the Higgs-gluon couplings and to the s-channel propagators entering the $gg \rightarrow hh$ amplitude. We discuss the numerical impact of the two-loop BSM contributions, first on the individual couplings and then on the prediction for the pair-production cross section, in two benchmark scenarios for the aligned THDM.

Figures (4)

• Figure 1: Left: Trilinear coupling modifier $\kappa_\lambda$ as function of a common pole mass $M_\Phi$ for the BSM Higgs bosons, in a benchmark scenario for the aligned THDM where $M^2=(600~{\rm GeV})^2$ and $\tan\beta=1.2$. The dot-dashed line is the one-loop result and the solid lines are two-loop results. The latter correspond to three different definitions of the parameter $M^2$, as explained in the text. Right: Same as in the left plot, for the scenario with $M_H^2 = M^2=(600~{\rm GeV})^2$ and $M_A^2=M_{H^\pm}^2 \equiv M_\Phi^2$.
• Figure 2: Left: Trilinear coupling $\lambda_{hhH}$ as function of a common pole mass $M_\Phi$ for the BSM Higgs bosons, in a benchmark scenario for the aligned THDM where $M^2=(600~{\rm GeV})^2$ and $\tan\beta=1.2$. The dot-dashed line is the one-loop result, the solid lines are two-loop results for three different definitions of the parameter $M^2$. Right: Same as in the left plot, for the scenario with $M_H^2 = M^2=(600~{\rm GeV})^2$, $M_A^2=M_{H^\pm}^2 \equiv M_\Phi^2$, and $\tan\beta=1.2$. Note the different scale on the $y$ axis w.r.t. the left plot.
• Figure 3: Top: Cross section for the production of a pair of SM-like Higgs bosons at the LHC with $\sqrt s = 13$ TeV, normalized to the SM prediction, as function of a common pole mass $M_\Phi$ for the BSM Higgs bosons, in a benchmark scenario for the aligned THDM where $M^2=(600~{\rm GeV})^2$ and $\tan\beta=1.2$. The meaning of the different lines is described in the text. Bottom: Ratios of the dashed lines over the solid lines.
• Figure 4: Same as figure \ref{['fig:XS1']} for the scenario with $M_H^2 = M^2=(600~{\rm GeV})^2$ and $M_A^2=M_{H^\pm}^2 \equiv M_\Phi^2$.