ILC Phenomenology of the $Z_3$ symmetric Type-Z Three Higgs Doublet Model

Abstract

The Three-Higgs-Doublet Model (3HDM) extends the Standard Model by introducing two additional scalar doublets, leading to a rich spectrum of new particles: three neutral CP-even Higgs bosons ($h_1$, $H_2$, $H_3$), two neutral CP-odd Higgs bosons ($A_2$, $A_3$), and two charged Higgs bosons ($H_2^+$, $H_3^+$). In this work, we present a phenomenological study of the 3HDM at the future International Linear Collider (ILC) with a center-of-mass energy of $\sqrt{s} = 1000\,\text{GeV}$. Applying a comprehensive set of theoretical and experimental constraints, we identify promising new physics signals with sufficiently large production cross-sections. Our analysis shows that $e^+e^- \to H_2 A_2$, $e^+e^- \to H_2 H_2 Z$, $A_2 A_2 Z$, $H_2 H_2^{\pm} W^{\mp}$, $A_2 H_2^{\pm} W^{\mp}$ and $H_1 H_2 A_2$ are among the most sensitive channels to probe this extended Higgs sector. We demonstrate that a future ILC would offer a powerful platform to test these interactions and discover these heavier Higgs bosons thus providing evidence of physics beyond the Standard Model.

Figures (4)

• Figure 1: A few illustrative Feynman diagrams for the $H_2A_2$ process.
• Figure 2: The plots in the upper panel represent the selection cuts applied to BP1. Both sets of plots show the selection cuts on $p_T(b_1)$ and $p_T(b_2)$. The shaded regions indicate the selected ranges that are implemented in the cutflow chart.
• Figure 3: Some sample kinematic distributions for the $H_2H_2Z$ decaying to a fully hadronic final state - as can be seen, the overlap of the signal and background distributions for much of the kinematic range does not permit a useful cut-based strategy in this case.
• Figure 4: Signal significance vs luminosity for all considered channels.