Triplet Scalars and Dark Matter at the LHC

TL;DR

This work analyzes the ΣSM, a minimal real triplet extension of the SM that preserves a SM-like Higgs while enriching the scalar sector. By examining vacuum structure, mass spectra, and interactions, the authors identify distinctive collider signatures, including light charged scalars, long-lived charged tracks when the triplet vev is tiny, and substantial modifications to the H_1→γγ decay amplitude via charged-H^± loops. They show that if the triplet vev vanishes, Σ^0 can be a cold dark matter component and the LHC can probe this scenario through monojet/monophoton plus track events or via diphoton channels, with the potential to constrain the quartic coupling a_2 and the masses M_{H_1}, M_{H_2}, M_{H^±}. The study also outlines discovery strategies across low- and high-mass regimes and discusses how future e^+e^− colliders could complement LHC searches to determine model parameters and distinguish the ΣSM from other extended Higgs sectors. δρ bounds and EWPO guide the viable parameter space, while distinctive decay and production patterns offer concrete paths to test the model experimentally, including the ratio tests in the heavy-Higgs regime.

Abstract

We investigate the predictions of a simple extension of the Standard Model where the Higgs sector is composed of one $SU(2)_L$ doublet and one real triplet. We discuss the general features of the model, including its vacuum structure, theoretical and phenomenological constraints, and expectations for Higgs collider studies. The model predicts the existence of a pair of light charged scalars and, for vanishing triplet vacuum expectation value, contains a cold dark matter candidate. When the latter possibility occurs, the charged scalars are long-lived, leading to a prediction of distinctive single charged track with missing transverse energy or double charged track events at the LHC. The model predicts a significant excess of two-photon events compared to SM expectations due to the presence of a light charged scalar.

Figures (20)

• Figure 1: Predictions for $\delta$, as defined in Eq. (\ref{['delta']}), in the case of $x_0=0$ and $M_{H_1}=120$ GeV. Left panel shows the $\delta$ dependence on $M_{H^+}$. Different curves correspond to different values of $a_2$. Right panel shows the $\delta$ dependence on $a_2$, with different curves corresponding to different charged Higgs masses, $M_{H^+}$.
• Figure 2: Values for $\delta$ in percent, as defined in Eq. (\ref{['delta']}), when $x_0=1$ GeV and $M_{H_1}=120$ GeV.
• Figure 3: Branching ratios for the singly charged Higgs as a function of $x_0$ for $M_{H_2}=150$ GeV $-\Delta M$ in Eq.(24) (left panel) and $M_{H_2}=300$ GeV $-\Delta M$ (right panel). Here, we have taken $M_{H_1}=120$ GeV.
• Figure 4: Branching ratios for the singly charged Higgs as a function of $M_{H^+}$ when $x_0=1$ GeV (left panel) and $x_0=10^{-6}$ (right panel) using $M_{H_1}=120$ GeV.
• Figure 5: Charged Higgs decay length as a function of $x_0$ for different values of $M_{H^+}$. The green line indicates the minimum needed for observation of a secondary vertex.