Abstract This work examines the $h\to Z\gamma$ and $h\to\gamma\gamma$ decays in the flavor-gauged two Higgs doublet model (FG2HDM), which augments the Standard Model (SM) with an additional scalar doublet, a singlet, and a $U(1)'$ flavor gauge symmetry. Beyond the SM spectrum, the FG2HDM predicts five additional physical scalars and a new neutral gauge boson, $Z'$. We demonstrate that while both decay channels are sensitive to charged Higgs loops, $h \to Z\gamma$ is uniquely modified by fermion-antifermion-$Z$ ($f\bar{f}Z$) vertex corrections. These vertex corrections further impact top-quark observables and the flavor-changing neutral current (FCNC) process $b\to s\ell^+\ell^-$. Our analysis identifies a viable parameter space ($m_{H^\pm}>200$~GeV and $\lambda_{hH^+H^-}<0$) consistent with current $1\sigma$ experimental limits, where the signal strength $\mu_{\gamma\gamma}$ remains the primary constraint on scalar sector parameters. Regarding the $f\bar{f}Z$ couplings, we delineate the allowed regions in the $\mathcal{Q}_{tL}$-$\mathcal{Q}_{tR}$ plane by evaluating the leading top-quark contributions, revealing that $b\to s\ell^+\ell^-$ imposes the most stringent bounds. Finally, we highlight that the $14\%$ projected precision for $\mu_{Z\gamma}$ at the High-Luminosity LHC (HL-LHC) will significantly enhance the sensitivity to the FG2HDM. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.

The present study aims to unveil a scenario with a nonminimal secluded dark sector (DS) in an effective field theory (EFT) framework. To explore this, we have examined a suitable extension of the type-X two Higgs doublet model (2HDM) as a potential origin for the secluded DS. The DS comprises a dark matter (DM) candidate and a mediator particle “ a ” and possesses some nonminimal characteristics. It becomes nonthermally populated through diverse dim-6 four-Fermi operators, effectively generated by integrating out the heavier Higgs particles. The analysis further focuses on the consequences of the collision processes DM + a ↔ a + a and DM + DM ↔ a + a occurring within the DS. We have investigated the significance of employing an EFT approach in tracking the temperature evolution of the DS. Within the present framework, the observed relic abundance of the DM can be realized through both dark freeze-out and freeze-in mechanisms. Further, we have delineated the permissible ranges of the relevant parameters, viz., the DM mass ( m χ ≳ 20 GeV ), the portal coupling ( C τ ≲ 10 − 14 GeV − 2 ), and the DS coupling ( λ ≲ 10 − 6 GeV − 2 ), by taking into account the perturbativity of the involved couplings while reproducing the observed DM relic and complying with the bounds from successful big bang nucleosynthesis (BBN) and γ -ray searches.

The Standard Model effective field theory (SMEFT) provides a robust framework for probing deviations in the couplings of Standard Model particles from their theoretical predictions. This framework relies on an expansion in higher-dimensional operators, often truncated at dimension-six. In this work, we compute the effective dimension-eight operators generated by integrating out heavy scalar fields at one-loop order in the Green’s basis within two extended scalar sector models: the two Higgs doublet model and the complex triplet scalar model. In this work, we consider loops that consist of heavy field propagators only. We also investigate the impact of heavy scalar fields on the fermion sector, deriving the fermionic effective operators up to dimension-eight for these models, and detail how contributions can be mapped onto nonredundant bases. To assess the importance of higher-order contributions in the SMEFT expansion, we analyze dimension-eight effects for electroweak precision observables at the next frontier of precision lepton machines such as GigaZ.

In this work, we explore how the 2-Higgs doublet model (2HDM) type-I, extended by an inert doublet, can provide an explanation for the recently observed excesses at the Large Hadron Collider (LHC) in the γ γ and τ + τ − final states. Hence, by imposing theoretical constraints and experimental bounds on the model parameter space, our findings show that a light C P -even Higgs boson, h , with a mass around 95 GeV, can account for these anomalies. This result aligns with the excess in b b ¯ signatures reported in earlier data from the Large Electron-Positron (LEP) collider.

We investigate a the constraints and phenomenology of a three Higgs doublet model (3HDM) with a [Formula: see text] symmetry, featuring two inert scalar doublets that give rise to a two-component dark matter (DM) scenario. We analyze the model’s vacuum structure, exploring the competition between different symmetry-breaking minima, and subject it to comprehensive theoretical and current experimental constraints. Our analysis reveals previously unexplored regions of parameter space with viable dark matter candidates. Notably, we identify scenarios where both DM particles contribute comparably to the observed relic density, offering distinctive experimental signatures that could guide future searches.

Study of the Relation Between Charged Yukawa Coupling Constants Under the Leptonic Specific Two Higgs Doublet Model

A bstract The origin of the baryon asymmetry of the universe remains one of the most pressing open questions in particle physics and cosmology. Electroweak baryogenesis offers an experimentally testable explanation, requiring new sources of CP violation and a strong first-order electroweak phase transition. The Two Higgs doublet model (2HDM) is the simplest scalar extension of the Standard Model that can accommodate both ingredients. We critically assess the viability of the complex 2HDM (C2HDM) (a 2HDM with a softly broken ℤ 2 symmetry and a single source of explicit CP violation in the Higgs sector) as a framework for electroweak baryogenesis, incorporating for the first time a comprehensive set of LHC Run 2 results at 13 TeV. By defining CP-violating benchmark planes tailored for a strong first-order electroweak phase transition, we identify regions of parameter space motivated by electroweak baryogenesis that will be testable at the LHC, and at future space-based gravitational wave experiments. The benchmark planes are intended to guide ongoing efforts in defining representative scenarios for the exploration of CP-violation in extended scalar sectors at the LHC Run 3 and beyond, while also assessing the emerging synergy between the LHC and future gravitational wave observatories such as LISA. We also quantify the current tension between the realisation of electroweak baryogenesis and the non-observation of the electron electric dipole moment (EDM), finding that the predicted electron EDMs typically exceed the experimental limits by at least an order of magnitude.

We explore the phenomenology of three Higgs doublet scenario, where the scalar potential is augmented by ℤ3 × ℤ2 symmetry making one doublet inert. Thus in effect, our model of interest is two Higgs plus inert Higgs doublet model charged under ℤ3((2+I)HDM-ℤ3) symmetry. We observe a blind spot feature for dark matter direct detection, as the tree-level dark matter-nucleon scattering cross-section vanishes depending on the mass splitting of dark sector particles. We perform a detailed analysis based on vacuum stability, unitarity, relic abundance, and direct detection results on the model. We also perform profile likelihood analysis and constrain the corresponding parameter space.

Recent experimental measurements of several observables in semileptonic B meson decays have pointed towards the possibility of new physics. The LHCb collaboration has reported a significant deviation, exceeding [Formula: see text], in the combined measurement of the ratio of branching ratios [Formula: see text] from the predictions of the standard model. Furthermore, other observables, such as [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] in the [Formula: see text] transition, have also exhibited noticeable deviations from the standard model predictions. Motivated by these anomalies in the [Formula: see text] transitions, we perform a log-likelihood fit incorporating new physics coming from right-handed neutrino couplings and explored the implications of a charged Higgs boson within a generic two Higgs doublet model (G2HDM). Our comprehensive analysis, focused on the [Formula: see text] and [Formula: see text] final states, was performed using the High Luminosity run of the Large Hadron Collider (HL-LHC). We demonstrate that HL-LHC has the sensitivity to exclude the remaining allowed region in G2HDM model in explaining these anomalies with charged Higgs boson coupled to right-handed neutrino.

Low scale leptogenesis and TM1 mixing in neutrinophilic two Higgs doublet model (ν2HDM) with S4 flavor symmetry

Large hadron collider signatures of exotic vector-like quarks within the 2-Higgs doublet model type-II

In 2022, the collider detector at Fermilab (CDF) collaboration reported the W-boson mass ( ), which deviates from the standard model (SM) prediction ( ) by ~ . In contrast, the CMS collaboration obtained , which was very close to the SM global electroweak fit value of . Motivated by this situation, we reassess the W-boson mass within the lepton-specific two Higgs doublet model (LS-2HDM). To this end, we perform random scans (generated with SARAH 4.13.0 and evaluated with SPheno 4.0.3) and confront the results with up-to-date theoretical and experimental constraints. The scan enforces vacuum stability, perturbative unitarity, and perturbativity; electroweak precision observables via the oblique parameters ; LEP bounds on ; rare B-meson decays; lepton flavor universality (LFU) in Z and τ decays; and 13 TeV LHC searches for additional Higgs bosons. Viable points are further tested with HiggsTools (HiggsSignals + HiggsBounds). In the LS-2HDM, if is the SM-like Higgs at GeV with , , GeV, and GeV, the model reproduces the 2024 CMS W-boson mass within . Solutions near the 2022 CDF value ( ) survive; however, after applying all constraints, including HiggsTools, they approach it at best within . Our findings emphasize that LS-2HDM favors the CMS results consistently with the current experimental results. Although one can theoretically accommodate the CDF results in this model, up-to-date electroweak precision bounds on oblique parameters with the SM-like Higgs and LFU constraints exclude these solutions. Our results for -boson mass can only be as close as about to the CDF results.

Abstract We study two Higgs doublet models with successful electroweak baryogenesis but without cancellations of electric dipole moments (EDMs). For the baryogenesis, additional scalar bosons are favored to couple mainly with the top quark with CP violations. However, if they also couple to light fermions of the Standard Model, the model is limited severely by EDMs, and additional CP phases irrelevant to the baryogenesis are often introduced to cancel the contributions to the EDMs. Alternatively, we consider a scenario where the light-fermion couplings are suppressed to avoid the constraints. In our scenario, it is found that the leading contributions arise in the top-quark EDMs at the two-loop level. They induce the electron, neutron, and proton EDMs via radiative corrections. Since there is no additional CP-violating phase, they are correlated with the baryon asymmetry. We show that our scenario is compatible with the current experimental bounds and is within the scope of future EDM experiments.

One of the standard ways to study scenarios beyond the Standard Model involves extending the Higgs sector. This work examines the three Higgs doublet model (3HDM) in a type-Z or democratic setup, where each Higgs doublet couples exclusively to a specific type of fermion. The particle spectrum of the 3HDM includes four charged Higgs bosons, two CP-odd scalars, and three CP-even scalars. This work investigates the allowed mass and coupling parameter space in the type-Z 3HDM after imposing all theoretical and experimental constraints. We extract the allowed parameter space under three distinct alignment-limit conditions or mass hierarchies leveraging machine learning techniques. Specifically, we analyze scenarios where the 125 GeV Higgs is the lightest, an intermediary, or the heaviest CP-even Higgs boson. Our findings indicate that while a single lighter CP-even Higgs boson below 125 GeV still remains a possibility, the presence of two lighter Higgses is ruled out. Published by the American Physical Society 2025

We investigate the LHC discovery prospects for a second Higgs doublet through A→ZH weak decay. The latter is identified as the of two Higgs doublet models (2HDMs) with first-order electroweak (EW) phase transition, a necessary condition for EW baryogenesis. In the general 2HDM (G2HDM) that has flavor-changing neutral Higgs couplings, H may decay dominantly via tc¯+t¯c final states, giving rise to trilepton signals. By a phenomenological analysis, we show that A→ZH in ℓ+ℓ−tc¯ or ℓ+ℓ−t¯c final states could be a promising probe of G2HDM at the LHC with flavor violation.

Both ATLAS and CMS have recently performed the first searches for a heavy new spin-0 resonance decaying into a lighter new spin-0 resonance and a Z boson, where the lighter spin-0 resonance subsequently decays into tt¯ pairs. These searches are of particular interest to probe Two Higgs doublet model (2HDM) parameter space regions that predict a strong first-order electroweak phase transition. In the absence of CP violation, the investigated decay is possible if the lighter and the heavier spin-0 particles have opposite CP parities. The analysis techniques employed by ATLAS and CMS do not distinguish between the two possible signatures A → ZH and H → ZA, where A and H denote CP-odd and CP-even Higgs bosons, respectively, if both signals are predicted to have the same total cross sections. We demonstrate the capability of angular variables that are sensitive to spin correlations of the top quarks to differentiate between A → ZH and H → ZA decays, even in scenarios where both signals possess identical total cross sections. Focusing on masses of 600 GeV and 800 GeV as a representative 2HDM benchmark, we find that a distinction between the two possible channels is possible with high significance with the anticipated data from the high-luminosity LHC, if the invariant mass distribution of the tt¯ system is further binned in angular variables defined by the direction of flight of the leptons produced in the top-quark decays. Moreover, we find a moderate gain in experimental sensitivity due to the improved background rejection for both signals.

We study the discovery potential for a light Higgs boson via gg→HSM−like→hh→bb¯γγ process at the Large Hadron Collider (LHC). Focusing on the 2-Higgs Doublet Model Type-I, which can accommodate light neutral Higgs states, of O(100) GeV or less in mass, while agreeing with theoretical and up-to-date experimental constraints, we explore the feasibility of a light CP-even Higgs state h via the largely unexplored final state bb¯γγ at Run-3 of the LHC. We further propose a few benchmark points for future searches. Published by the American Physical Society 2025

The charged Kaon meson ([Formula: see text]) features several hadronic decay modes, but the most relevant contribution to its decay width stems from the leptonic decay [Formula: see text]. Given the precision acquired on the rare decay mode [Formula: see text], one can use the data to set constraints on sub-GeV hidden sectors featuring light species that could contribute to it. Light gauge bosons that couple to muons could give rise to sizeable contributions. In this work, we will use data from the [Formula: see text] and [Formula: see text] decays to place limits on light vector bosons present in Two Higgs Doublet Models (2HDM) augmented by an Abelian gauge symmetry, 2HDM-[Formula: see text]. We put our findings into perspective with collider bounds, atomic parity violation, neutrino-electron scattering, and polarized electron scattering probes to show that rare Kaon decays provide competitive bounds in the sub-GeV mass range for different values of [Formula: see text].

The results obtained at the LHC for constraining the trilinear Higgs self-coupling of the detected Higgs boson at about 125 GeV, λhhh, via the Higgs pair production process have significantly improved during the last years. We investigate the impact of potentially large higher-order corrections and interference effects on the comparison between the experimental results and the theoretical predictions for the pair production of the 125 GeV Higgs boson at the LHC. We use the theoretical framework of the Two Higgs Doublet Model (2HDM), containing besides the SM-like CP-even Higgs boson h a second CP-even Higgs boson H, which we assume to be heavier, mH>mh mh$$\\end{document}]]>. We analyze in particular the invariant mass distribution of the two produced Higgs bosons and show that the loop corrections to the trilinear Higgs couplings λhhh and λhhH as well as interference contributions give rise to important effects both for the differential and the total cross section. We point out the implications for the experimental limits that can be obtained in the 2HDM for the case of the resonant production of the heavy Higgs boson H. We emphasize the importance of the inclusion of interference effects between resonant and non-resonant contributions in the experimental analysis for a reliable determination of exclusion bounds for a heavy resonance of an extended Higgs sector.

The coupling of the Higgs boson to first and second generation fermions has yet to be measured experimentally. There still could be very large deviations in these couplings, as the origin of flavor is completely unknown. Nevertheless, if Yukawa couplings are modified, especially for light generations, there are generically strong constraints from flavor-changing neutral currents (FCNCs). Therefore, it is imperative to understand whether there exists viable UV physics consistent with current data that motivates future Higgs coupling probes. In particular, the charm-quark Yukawa is the next quark coupling that could be measured at the LHC if it is a few times larger than the SM and compatible with flavor data. This is difficult to achieve in the context of standard ansatz such as Minimal Flavor Violation. In this paper we show that within the framework of Spontaneous Flavor Violation (SFV), using a Two Higgs Doublet Model as an example, the Higgs can be sufficiently charming that new LHC probes are relevant. In this charming region, we show that new Higgs states near the EW scale with large couplings to quarks are required, providing complementary observables or new constraints on the SM Yukawa couplings. The down-type SFV mechanism enabling the suppression of FCNCs also allows for independent modifications to the up-quark Yukawa coupling, which we explore in detail as well.