In this paper, we examine the consistency of the Large Hadron Collider (LHC) data collected during Runs 1 and 2 by the ATLAS and CMS experiments with the predictions of a 2-Higgs doublet model embedding vectorlike quarks (VLQs) for $pp\to H$, $A$ production and $H$, $A\to \gamma \gamma$ decay mechanisms, respectively, of (nearly) degenerate $CP$-even ($H$) and $CP$-odd ($A$) Higgs bosons. We show that a scenario containing one single VLQ with electromagnetic charge $2/3$ can explain the above ATLAS and CMS data for masses in the region $350\mathrm{GeV}\le m_{\mathrm{VLQ}}\le 1.5\mathrm{TeV}$ or so, depending on $\tan \beta$, and for several values of the mixing angle between the top quark ($t$) and its VLQ counterpart ($T$). We then perform a global fit onto the model by including all relevant experimental as well as theoretical constraints. The surviving samples of our analysis are discussed within $2\sigma$ of the LHC measurements. Additionally, we also comment on the recent anomalous result reported by CMS using Run 2 data on the associated Standard Model Higgs boson production with top quark pairs $pp\to t\overline{t}h$ with an observed significance of $3.3\sigma$. Other than these specific examples, we also present a phenomenological analysis of the main features of the model, including the most promising $T$ decay channels.

At the Large Hadron Collider (LHC), both the ATLAS and CMS Collaborations have been searching for light charged Higgs bosons via top (anti)quark production and decays channels, like pp → t $$ \overline{t} $$t ¯ with one top (anti)quark decaying into a charged Higgs boson and a b (anti)quark, when the decay is kinematically open (i.e., when $$ {m}_{H^{\pm }} $$m H ± ≲ m_t). In this paper, we propose new searches at the LHC involving light charged Higgs bosons via their pair production channels like pp → H^±h/A and pp → H⁺H⁻ in the 2-Higgs Doublet Model (2HDM) Type-I and -X scenarios. By focusing on the case where the heavy H state plays the role of the Standard Model (SM)-like Higgs boson with a mass near 125 GeV, we study the aforementioned Higgs boson pair production channels and investigate their bosonic decays, such as H^± → W^±h and/or H^± → W^±A. We demonstrate that for a light charged Higgs boson state, with $$ {m}_{H^{\pm }} $$m H ± ≲ m_t, at the LHC, such di-Higgs production and decay channels can give rise to signatures with event rates much larger than those emerging from pp → t $$ \overline{t} $$t ¯ → t $$ \overline{b} $$b ¯ H⁻ + c.c. We specifically study h/A → b $$ \overline{b} $$b ¯ and τ⁺τ⁻ decays. We, therefore, claim that the discussed combination of new production and decay modes can result in an alternative discovery channel for charged Higgs bosons lighter than the top (anti)quark at the LHC within the above two 2HDM Types. Finally, in order to motivate experimentalists in ATLAS and CMS to search for such signatures, we propose 16 Benchmark Points (BPs) which are compatible with both theoretical and experimental constraints.

We analyse a light charged Higgs boson in the 2-Higgs Doublet Model (2HDM) Type-I, when its mass satisfies the condition M_H±< M_t + M_b and the parameter space is consistent with theoretical requirements of self-consistency as well as the latest experimental constraints from Large Hadron Collider (LHC) and other data. Over such a parameter space, wherein the Standard Model (SM)-like state discovered at the LHC in 2012 is the heaviest CP-even state of the 2HDM, it is found that the decay modes of the charged Higgs boson are dominated by H^±→ W^±(∗)h. Furthermore, the light neutral Higgs boson h dominantly decays into two photons. Under these conditions, we find that the production and decay process pp → H^±h → W^±(∗)hh → ℓν_ℓ + 4γ (ℓ = e, μ) is essentially background free. However, since the W^±(∗) could be largely off-shell and the h state is very light, so that both the lepton coming from the former and the photons coming from the latter could be rather soft, we perform here a full Monte Carlo (MC) analysis at the detector level demonstrating that such a W^± + 4γ signal is very promising, as it would be yielding significant excesses at the LHC with an integrated luminosity of L = 300 fb⁻¹ at both $$ \sqrt{s} $$s = 13 and 14 TeV.