Narrow Results

The left–right twin Higgs (LRTH) model predicts the existence of the charged Higgs ϕ^±. In this paper, we study the production of the charged Higgs boson ϕ^- with single top quark via the process bg → tϕ^- at the CERN Large Hadron Collider (LHC). The numerical results show that the production cross-section can reach the level of 10 pb in the reasonable parameter space of the LRTH model. We expect that, as long as it is not too heavy, the possible signatures of the heavy charged Higgs boson ϕ^-> might be detected via the decay mode at the LHC experiments.

The D0 experiment has reported a direct search for a charged Higgs boson produced by annihilation and decaying to final state, in the 180≤M_H⁺≤300 GeV mass range. The analysis has led to upper limits on the production cross-section in the framework of the two-Higgs doublet model types I, II and III. We compare the predictions of two different scenarios in the framework of the two-Higgs doublet type III to the cross-section limits reported by D0 collaboration, and we obtain constraints on the charged Higgs mass, for the case when the charged Higgs mass is bigger than the top quark mass. Also, searches for the charged Higgs boson with a mass smaller than top quark mass are considered, we discuss the possible limits on the charged Higgs boson mass obtained from measurements of the ratio within the two-Higgs doublet model type III.

Production of charged Higgs boson associated with a W gauge boson at the LHC is mainly induced by the tree-level annihilation and the one-loop gg fusion. In the context of the Higgs triplet model (HTM) and the left–right twin Higgs (LRTH) model, we calculate the production cross-section σ of the process pp→H^±W^∓ and compare our results with those given by supersymmetry (SUSY). We find that, in most of the parameter space of the HTM, the production cross-section σ is smaller than that predicted by the LRTH model or SUSY. The value of σ within the LRTH model is larger or smaller than the SUSY case, which depends on the relevant free parameters.

The constraints from the measurements of the $B\to X_s\gamma$ decay rate on the parameter space of 3-Higgs Doublet Models (3HDMs), where all the doublets have nonzero vacuum expectation values, are studied at the next-to-leading order in QCD. In order to naturally avoid the presence of flavour changing neutral currents at the tree level, we impose two softly-broken discrete $Z_2$ symmetries. This gives rise to five independent types of 3HDMs that differ in their Yukawa couplings. We show that in all these 3HDMs (including the case of type-II-like Yukawa interactions) both masses of the two charged Higgs bosons $m_{H_1^{\pm }}$ and $m_{H_2^{\pm }}$ can be smaller than the top mass $m_t$ while complying with the constraints from $B\to X_s\gamma$. As an interesting phenomenological consequence, the branching ratios of the charged Higgs bosons decay into the $cb$ final states can be as large as $80\%$ when their masses are taken to be below $m_t$ in two of the five 3HDMs (named as Type-Y and Type-Z). This light charged Higgs boson scenario provides a hallmark 3HDM signature that cannot be realised in $Z_2$ symmetric 2-Higgs doublet models. We find that in the Type-Y and Type-Z 3HDMs the scenario with $90\mathrm{\text{GeV}}<m_{H_1^{\pm }}$, $m_{H_2^{\pm }}<m_t$ is ruled out by the direct searches at the LHC, but in the Type-Y 3HDM $80\text{GeV}<m_{H_1^{\pm }}<90\text{GeV}$ and $90\text{GeV}<m_{H_2^{\pm }}<m_t$ is allowed by $B\to X_s\gamma$ and direct searches at LEP2, Tevatron and LHC due to the reduced sensitivity of these searches to the degenerate case $m_{H_1^{\pm }}\approx m_{W^{\pm }}$. The cases where only one or both charged Higgs bosons are above the top quark mass are also naturally allowed in the both Type-Y and Type-Z 3HDMs.

In the Standard Model (SM), the $\rho$ parameter is equal to 1 and the ratio ${\lambda }_{WZ}$ of Higgs $\to ZZ$ and Higgs $\to WW$ is also equal to 1 at the tree level. When going beyond the SM with more than one type of Higgs representations, these quantities may be different from the SM predictions which can provide crucial information about new physics. There may also exist a certain charged Higgs $h^{+}$ decays into a $W^{+}$ and a $Z$. Imposing a custodial symmetry can force the parameter $\rho$ to be equal to 1 with certain predictions for ${\lambda }_{WZ}$ and $h^{+}\to W^{+}Z$. However, imposing $\rho =1$ without custodial symmetry may have different predictions. We show how differences arise and how to use experimental data to obtain information about the underlying physics in a model with the SM, plus a real and a complex $SU{(2)}_L$ triplet.

In particle physics, search for signals of new particles in the proton–proton collisions is an ongoing effort. The energies and luminosities have reached a level where new search techniques are becoming a necessity. In this work, we develop a search technique for light-charged Higgs boson (nearly degenerate with $W$-boson), which is extremely hard to do with the traditional cut-based methods. To this end, we employ a deep anomaly detection approach to extract the signal (light-charged Higgs particle) from the vast $W$-boson background. We construct a Deviation Network (DevNet) to directly obtain anomaly scores used to identify signal events using background data and few labeled signal data. Our results show that DevNet is able to find regions of high efficiency and gives better performance than the autoencoders, the classic semi-supervised anomaly detection method. It shows that employing Deviation Networks in particle physics can provide a distinct and powerful approach to search for new particles.