Di-Higgs Peaks and Top Valleys: Interference Effects in Higgs Sector Extensions

TL;DR

This paper compares interference effects in double Higgs and top quark final states within extended scalar models, revealing that di-Higgs searches may have underestimated discovery potential due to interference phenomena.

Contribution

It provides a detailed analysis of interference effects in BSM models, highlighting their impact on the relative sensitivity of di-Higgs and top pair resonance searches.

Findings

Top pair signals are suppressed by destructive interference.

Double Higgs signals can be enhanced by signal-signal interference.

Production cross section estimates remain accurate within 10% for di-Higgs final states.

Abstract

In models with extended scalars and CP violation, resonance searches in double Higgs final states stand in competition with related searches in top quark final states as optimal channels for the discovery of beyond the Standard Model (BSM) physics. This complementarity is particularly relevant for benchmark scenarios that aim to highlight multi-Higgs production as a standard candle for the study of BSM phenomena. In this note, we compare interference effects in $t\bar t$ final states with correlated phenomena in double Higgs production in the complex singlet and the complex 2-Higgs-Doublet Models. Our results indicate that the BSM discovery potential in di-Higgs searches can be underestimated in comparison to $t\bar t $ resonance searches. Top pair final states are typically suppressed due to destructive signal-background interference, while $hh$ final states can be enhanced due to signal-signal interference. For parameter choices where the two heavy Higgs resonances are well separated in mass, top final states are suppressed relative to the naive signal expectation, while estimates of the production cross section times branching ratio remain accurate at the ${\cal{O}}(10\%)$ level for double Higgs final states.