E6 GUT and Baryon Asymmetry Generation in the E6CHM

Grand unified theories (GUTs) may result in the E6-inspired composite Higgs model (E6CHM) at low energies, almost stabilizing the electroweak scale. We consider an orbifold GUT in 6 dimensions in which the E6-gauge group is broken to the gauge symmetry of the standard model (SM) while different multiplets of the SM fermions come from different 27-plets. The strongly coupled sector of the E6CHM is confined on the brane where E6 is broken down to its SU(6) subgroup. Near the scale of f≳5TeV, this approximate SU(6) symmetry is expected to be further broken down to its SU(5) subgroup, which contains the SM-gauge group. Such a breakdown leads to a set of pseudo-Nambu–Goldstone bosons (pNGBs) that includes an SM-like Higgs doublet. The approximate gauge coupling unification in the E6CHM takes place at high energies when the right-handed top quark is a composite fermion. To ensure anomaly cancellation, the weakly coupled sector of this model contains extra exotic matter beyond the SM. We discuss the mechanism of the generation of matter–antimatter asymmetry within the variant of the E6CHM in which the baryon number and CP invariance are violated.

The $$R^2$$-Higgs inflation with two Higgs doublets

We study $$R^2$$ R 2 -Higgs inflation in a model with two Higgs doublets in which the Higgs sector of the Standard Model is extended by an additional Higgs doublet, thereby four scalar fields are involved in the inflationary evolutions. We first derive the set of equations required to follow the inflationary dynamics in this two Higgs doublet model, allowing a nonminimal coupling between the Higgs-squared and the Ricci scalar R, as well as the $$R^2$$ R 2 term in the covariant formalism. By numerically solving the system of equations, we find that, in parameter space where a successful $$R^2$$ R 2 -Higgs inflation are realized and consistent with low energy constraints, the inflationary dynamics can be effectively described by a single slow-roll formalism even though four fields are involved in the model. We also argue that the parameter space favored by $$R^2$$ R 2 -Higgs inflation requires nearly degenerate masses for $$m_{\mathsf {H}}$$ m H , $$m_A$$ m A and $$m_{{\mathsf {H}}^{\pm }}$$ m H ± , where $${\mathsf {H}}$$ H , A, and $${\mathsf {H}}^{\pm }$$ H ± are the extra CP even, CP odd, and charged Higgs bosons in the general two Higgs doublet model taking renormalization group evolutions of the parameters into account. Discovery of such heavy scalars at the Large Hadron Collider (LHC) are possible if they are in the sub-TeV mass range. Indirect evidences may also emerge at the LHCb and Belle-II experiments, however, to probe the quasi degenerate mass spectra one would likely require high luminosity LHC or future lepton colliders such as the International Linear Collider and the Future Circular Collider.

Likelihood analysis of the flavour anomalies and g – 2 in the general two Higgs doublet model

We present a likelihood analysis of the general two Higgs doublet model, using the most important currently measured flavour observables, in view of the anomalies in charged current tree-level and neutral current one-loop rare decays of B mesons in b → cl$$ \overline{\nu} $$ ν ¯ and b → sμ+μ− transitions, respectively. We corroborate that the model explains the latter and it is able to simultaneously fit the experimental values of the R(D) charged current ratio at 1σ, but it can not accommodate the D* charmed meson observables R(D*) and FL(D*). We find that the fitted values for the angular observables in b → sμ+μ− transitions exhibit better agreement with the general two Higgs double model in comparison to the SM. We also make predictions for future collider observables BR(t → ch), BR(h → bs), BR(h → τμ), BR(Bs → τ+τ−), BR(B+ → K+τ+τ−) and the flavour violating decays of the τ lepton, BR(τ → 3μ) and BR(τ → μγ). The model predicts values of BR(t → ch), BR(Bs → τ+τ−) and BR(B+ → K+τ+τ−) that are out of reach of future experiments, but its predictions for BR(h → bs) and BR(h → τμ) are within the future sensitivity of the HL-LHC or the ILC. We also find that the predictions for the τ → 3μ and τ → μγ decays are well within the projected limits of the Belle II experiment. Finally, using the latest measurement of the Fermilab Muon g − 2 Collaboration, we performed a simultaneous fit to ∆aμ constrained by the charged anomalies, finding solutions at the 1σ level. Once the neutral anomalies are included, however, a simultaneous explanation is unfeasible.

Electroweak phase transitions with BSM fermions

We study the impact of additional beyond-the-Standard Model (BSM) fermions, charged under the Standard Model (SM) SU(2)L ⊗ U(1)Y gauge group, on the electroweak phase transition (EWPT) in a 2-Higgs-Doublet-Model (2HDM) of type II. We find that the strength of the EWPT can be enhanced by about 40% compared to the default 2HDM. Therefore, additional light fermions are a useful tool to weaken the tension between increasing mass constraints on BSM scalars and the requirement of additional light scalar degrees of freedom to accommodate a strong first order EWPT. The findings are of particular interest for a variety of (non-minimal) split supersymmetry scenarios which necessarily introduce additional light fermion degrees of freedom.

New Light H± Discovery Channels at the LHC

A light charged Higgs boson has been searched for at the Large Hadron Collider (LHC) via top (anti)quark decay, i.e., t→bH+, if kinematically allowed. In this contribution, we propose new channels for light charged Higgs boson searches via the pair productions pp→H±h/A and pp→H+H− at the LHC in the context of the Two-Higgs Doublet Model (2HDM) Type-I. By focusing on a case where the heavy H state is the Standard Model (SM)-like one already observed, we investigate the production of the aforementioned charged Higgs bosons and their bosonic decay channels, namely, H±→W±h and/or H±→W±A. We demonstrate that such production and decay channels can yield substantial alternative discovery channels for H± bosons at the LHC. Finally, we propose eight benchmark points (BPs) to motivate the search for such signatures.

Electroweak symmetry non-restoration from dark matter

Restoration of the electroweak symmetry at temperatures around the Higgs mass is linked to tight phenomenological constraints on many baryogenesis scenarios. A potential remedy can be found in mechanisms of electroweak symmetry non-restoration (SNR), in which symmetry breaking is extended to higher temperatures due to new states with couplings to the Standard Model. Here we show that, in the presence of a second Higgs doublet, SNR can be realized with only a handful of new fermions which can be identified as viable dark matter candidates consistent with all current observational constraints. The competing requirements on this class of models allow for SNR at temperatures up to ∼TeV, and imply the presence of sub-TeV new physics with sizable interactions with the Standard Model. As a result this scenario is highly testable with signals in reach of next-generation collider and dark matter direct detection experiments.

Generalized 2HDM with wrong-sign lepton-Yukawa coupling, in light of $$g_{\mu }-2$$ and lepton flavor violation at the future LHC

To explain the observed muon anomaly and simultaneously evade bounds from lepton flavor violation in the same model parameter space is a long-cherished dream. In view of a generalized Two Higgs Doublet Model, with a Yukawa structure as a perturbation of Type-X, we are able to get substantial parameter space satisfying these criteria. In this work, we focus on a region with “wrong-sign” lepton-Yukawa coupling which gives rise to interesting phenomenological consequences. Performing a simple cut-based analysis, we show that at 14 TeV run of the LHC with $$300 \mathrm{{fb}}^{-1}$$ 300 fb - 1 integrated luminosity, part of the model parameter space can be probed with significance "Equation missing" which further improves with Artificial Neural Network analysis.

Solving the electron and muon $$g-2$$ anomalies in $$Z'$$ models

We consider simultaneous explanations of the electron and muon $$g-2$$ g - 2 anomalies through a single $$Z'$$ Z ′ of a $$U(1)'$$ U ( 1 ) ′ extension to the Standard Model (SM). We first perform a model-independent analysis of the viable flavour-dependent $$Z'$$ Z ′ couplings to leptons, which are subject to various strict experimental constraints. We show that only a narrow region of parameter space with an MeV-scale $$Z'$$ Z ′ can account for the two anomalies. Following the conclusions of this analysis, we then explore the ability of different classes of $$Z'$$ Z ′ models to realise these couplings, including the SM$$+U(1)'$$ + U ( 1 ) ′ , the N-Higgs Doublet Model$$+U(1)'$$ + U ( 1 ) ′ , and a Froggatt–Nielsen style scenario. In each case, the necessary combination of couplings cannot be obtained, owing to additional relations between the $$Z'$$ Z ′ couplings to charged leptons and neutrinos induced by the gauge structure, and to the stringency of neutrino scattering bounds. Hence, we conclude that no $$U(1)'$$ U ( 1 ) ′ extension can resolve both anomalies unless other new fields are also introduced. While most of our study assumes the Caesium $$(g-2)_e$$ ( g - 2 ) e measurement, our findings in fact also hold in the case of the Rubidium measurement, despite the tension between the two.