Higgs Singlet Research Articles

Top quark decays in the flavor-dependent U(1)X model

The branching ratios of the flavor changing top quark decays in the SM are too small to be detected experimentally. Therefore, any observable signal for these processes at the LHC would serve as compelling evidence for new physics. In the flavor-dependent U(1)X model, a newly introduced Higgs singlet interacts directly with the quark sector and mixes with the SM-like Higgs, influencing the t→ch and t→uh process. Additionally, the flavor dependence of the U(1)X charge affect the t→cZ process. In this work, we investigate these process within the framework of the flavor-dependent U(1)X model. Numerical results indicates that with suitable choices of new physics parameters, the branching ratios of these processes in the flavor-dependent U(1)X model can be significantly enhanced. Specifically, the branching ratios of t→ch and t→uh can reach the order of 10-4 in some chosen parameter spaces, which is close to the current experimental upper limit. This suggests that these processes have significant opportunities to be observed experimentally, and the parameter space of the model will face constraints from the experimental upper bounds.

The Higgs boson decay h → bs in the U(1)XSSM

In the U(1)XSSM, we delve into the quark flavor violation of h → bs, where h is identified as the SM-like Higgs boson discovered at the LHC. As the U(1) extension of the minimal supersymmetric standard model (MSSM), the U(1)XSSM has new super fields such as right-handed neutrinos and three Higgs singlets. We conduct a thorough analysis of the underlying mechanisms and parameter dependencies of h → bs in the U(1)XSSM. In the U(1)XSSM, we discover that the Br(h → bs) for the Higgs decay to bs could significantly differ from the expectation in the standard model (SM), depending on the values of the new parameters introduced in the model. Our research not only contributes to a deeper understanding of Higgs physics within the U(1)XSSM, but also provides valuable guidance for new physics (NP).

Top-quark FCNC decays, LFVs, lepton g − 2, and W mass anomaly with inert charged Higgses

The observed flavor-changing neutral-current (FCNC) processes in the standard model (SM) arise from the loop diagrams involving the weak charged currents mediated by the W-gauge boson. Nevertheless, the top-quark FCNCs and lepton flavor-violating processes resulting from the same mechanism are highly suppressed. We investigate possible new physics effects that can enhance the suppressed FCNC processes, such as a top quark decaying into a light quark with a Higgs or gauge boson in the final state, i.e. t → q(h, V) with V = γ, Z, g, h→ℓℓ′ , and ℓ→ℓ′γ . To achieve the assumption that the induced FCNCs are all from quantum loops, we consider the scotogenic mechanism, where a Z 2 symmetry is introduced and only new particles carry an odd Z 2 parity. With the extension of the SM to include an inert Higgs doublet, an inert charged Higgs singlet, a vector-like singlet quark, and two neutral leptons, it is found that, with relevant constraints taken into account, the t → c(h, Z), h → μ τ, and τ → ℓ γ decays can be enhanced up to the expected sensitivities in experiments. The branching ratios of h → μ + μ −/τ + τ − from only new physics effects can reach up to O(10−3) . Intriguingly, the resulting muon g − 2 can fit the combined data within 2 standard deviations, whereas the electron g − 2 can have either sign with a magnitude of O(10−13−10−12) . In addition, we examine the oblique parameters in the model and find that the resulting W-mass anomaly observed by CDF II can be accommodated.

Top-quark rare decays with flavor violation* *This work is supported by the National Natural Science Foundation of China (12075074), the Natural Science Foundation of Hebei Province, China (A2020201002, A2022201022, A2022201017, A2023201040), the Natural Science Foundation of Hebei Education Department, China (QN2022173), the Post-graduate's Innovation Fund Project of Hebei University (HBU2024SS042), and the Youth Top-notch Talent Support Program of the Hebei

In the present study, we investigated the decays of the top quark: , , , and . They are extremely rare processes in the standard model (SM). As the extension of the minimal supersymmetric standard model (MSSM), the SSM features new superfields such as the right-handed neutrinos and three Higgs singlets. We analyzed the effects of different sensitive parameters on the results and made reasonable theoretical predictions, thereby providing a useful reference for future experimental development. Considering the constraint set by the updated experimental data, the numerical results show that the branching ratios of the four processes, i.e., , can reach the same order of magnitude as their experimental upper limits. Among them, has the most evident effect on these processes and is the main parameter; , , , , , , and are also important parameters for the processes, and have effects on the numerical results.

H-COUP Version 3: A program for one-loop corrected decays of any Higgs bosons in non-minimal Higgs models

The H-COUP program is provided as a package of Fortran codes, which can compute observables related to Higgs bosons including radiative corrections in various extended Higgs sectors. We give a manual for the latest version of H-COUP (H-COUP_3.0), in which decay rates and branching ratios of all the Higgs bosons can be calculated at one-loop level in EW and Higgs interactions with QCD corrections in the Higgs singlet model, four types of the two Higgs doublet model with a softly-broken Z2 symmetry, and the inert doublet model. The previous version (H-COUP_2.0) can evaluate those only for the standard model like Higgs boson with the mass of 125 GeV (h). In H-COUP_3.0, renormalized quantities are computed based on the gauge-independent on-shell renormalization scheme. The source code of H-COUP_3.0 can be downloaded via the following link: http://www-het.phys.sci.osaka-u.ac.jp/~hcoup. By using H-COUP_3.0, we can compare the precise measurements of the properties of h and direct searches for additional Higgs bosons with their predictions at one-loop level, by which we can reconstruct the structure of the Higgs sector. New version program summaryProgram Title: H-COUP Version 3 5CPC Library link to program files:https://doi.org/10.17632/f88szmrj5x.3Developer's repository link:http://www-het.phys.sci.osaka-u.ac.jp/~hcoupLicensing provisions: GPLv3Programming language: Fortran90Journal reference of previous version: Comput. Phys. Commum. 257 (2020) 107512Does the new version supersede the previous version?: YesReasons for the new version: The previous version (H-COUP version 2) is a package of Fortran codes to provide one-loop corrected couplings, decay rates and branching ratios of the 125 GeV Higgs boson in the Higgs Singlet Model (HSM), the Two Higgs doublet models (THDMs) with a softly-broken Z2 symmetry, and the Inert Doublet Model (IDM). In the new version (H-COUP version 3), the H-COUP program has been improved to calculate the decay rates and the branching ratios of all the Higgs bosons including one-loop corrections in the above models. These calculations are performed based on the gauge independent on-shell renormalization scheme.Summary of revisions: We have added radiatively corrected decay rates and branching ratios for all the additional Higgs bosons, not only for the 125 GeV Higgs boson, in the extended Higgs models. Furthermore, several choices are provided for renormalization schemes used to evaluate electroweak corrections. The scalar two-point functions are renormalized by on-shell scheme as in the previous version, while the renormalization for the tadpole is performed by either the standard tadpole scheme or the alternative tadpole scheme. The users can choose these renormalization schemes.Nature of problem: Decay rates and branching ratios of all the Higgs bosons can be calculated with one-loop electroweak corrections and QCD corrections in the HSM, four types of the THDMs with the softly-broken Z2 symmetry, and the IDM. In the calculations of additional Higgs boson decays, for the three-body decay processes and loop induce processes of additional Higgs bosons, electroweak corrections are not included. As for the QCD correction, next-to-leading order or next-to-next-to-leading order corrections are included, depending on the decay process.Solution method: Electroweak corrections are evaluated based on the gauge independent on-shell renormalization scheme, while some parameters are renormalized by the MS‾ scheme. QCD corrections are evaluated with the MS‾ scheme.Additional comments including restrictions and unusual features: All functions up to the previous version are included in H-COUP version 3.

Solving the strong CP problem via a -characterized mirror symmetry* *Supported in part by the National Natural Science Foundation of China (12175038) and in part by the Fundamental Research Funds for the Central Universities

In the standard model QCD Lagrangian, a term of CP violating gluon density is theoretically expected to have a physical coefficient , which is typically on the order of unity. However, the upper bound on the electric dipole moment of the neutron enforces the value of to be extremely small. The significant discrepancy between theoretical expectations and experimental results in this context is widely recognized as the strong CP problem. To solve this puzzle in an appealing context of two Higgs doublets, we propose a -characterized mirror symmetry between two Higgs singlets with respective discrete symmetries. In our scenario, the parameter can completely disappear from the full Lagrangian after the standard model fermions take a proper phase rotation as well as the Higgs doublets and singlets. Moreover, all of new physics for solving the strong CP problem can be allowed near the TeV scale.

Physics implication from higher weak isospin decomposition

The SU(3)_Lotimes U(1)_X symmetry actually studied is directly broken to the electroweak symmetry SU(2)_Lotimes U(1)_Y by a Higgs triplet, predicting a relevant new physics at TeV scale. This work argues, by contrast, that the higher weak isospin SU(3)_L might be broken at a high energy scale, much beyond 1 TeV, by a Higgs octet to an intermediate symmetry SU(2)_Lotimes U(1)_{T_8} at TeV, before the latter U(1)_{T_8} recombined with U(1)_X defines (i.e., broken to) U(1)_Y by a Higgs singlet. The new physics coupled to SU(3)_L breaking phase is decoupled, whereas what remains is a novel family-nonuniversal abelian model, U(1)_{T_8}otimes U(1)_X, significantly overhauling the standard model as well as yielding consistent results for neutrino mass, dark matter, W-mass anomaly, and FCNC, differently from the usual 3-3-1 model.

Formula omitted] universal seesaw

We extend the SU(3)c×SU(2)L×U(1)Y standard model by a U(1)Y′ gauge symmetry. Three right-handed neutrinos are introduced to cancel the gauge anomaly. One Higgs singlet is responsible for spontaneously breaking the U(1)Y′ symmetry while the standard model Higgs doublet does not carry any U(1)Y′ charges. The down-type quarks, up-type quarks, charged leptons and neutral neutrinos obtain their Dirac masses through four types of dimension-5 operators constructed by the fermion doublets and singlets with the Higgs doublet and singlet. This effective theory is realized in three renormalizable contexts with heavy fermion singlets, scalar doublets and fermion doublets. The heavy fermion singlets and doublets for generating the neutrino masses also accommodate a successful Dirac leptogenesis to explain the baryon asymmetry in the universe.

A Study of the Higgs Mass with the Effective Potential and Higgs Decays in the U(1)XSSM

As the U(1) extension of the minimal supersymmetric standard model, the U(1)XSSM has new superfields, such as right-handed neutrinos, and three Higgs singlets. In the U(1)XSSM, the lightest CP-even Higgs mass mh0 is studied by using the Higgs effective potential with one-loop corrections. We also calculate the Higgs decays h0→γγ, h0→VV(V=W,Z), h0→ll¯Z, and h0→νν¯Z. The obtained results are reasonable, and they are in favor of the study of the Higgs characteristic and the phenomenology of the U(1)XSSM.

Phenomenology of a 96 GeV Higgs boson in the 2HDM with an additional singlet

We discuss a $\ensuremath{\sim}3\ensuremath{\sigma}$ signal (local) in the light Higgs-boson search in the diphoton decay mode at $\ensuremath{\sim}96\text{ }\text{ }\mathrm{GeV}$ as reported by CMS, together with a $\ensuremath{\sim}2\ensuremath{\sigma}$ excess (local) in the $b\overline{b}$ final state at the Large Electron Positron Collider (LEP) in the same mass range. We interpret this possible signal as a Higgs boson in the 2 Higgs doublet model type II with an additional Higgs singlet, which can be either complex (2HDMS) or real (N2HDM), where the 2HDMS so far has never been analyzed as an explanation of these excesses. An emphasis of our work is the differences between and the possible distinction of the two models in this context. We find that the lightest $\mathcal{C}\mathcal{P}$-even Higgs boson of the two models can equally yield a perfect fit to both excesses simultaneously, while the second lightest state is in full agreement with the Higgs-boson measurements at 125 GeV, and the full Higgs-boson sector is in agreement with all Higgs exclusion bounds from LEP, the Tevatron and the LHC as well as other theoretical and experimental constraints. We derive bounds on the 2HDMS and N2HDM Higgs sectors from a fit to both excesses and describe how this signal can be further analyzed at future ${e}^{+}{e}^{\ensuremath{-}}$ colliders, such as the International Linear Collider (ILC). We analyze in detail the anticipated precision of the coupling measurements of the 96 GeV Higgs boson at the ILC. We find that these Higgs-boson measurements at the LHC and the ILC cannot distinguish between the two Higgs-sector realizations.

Study of lepton EDMs in the U(1) X SSM * *Supported by National Natural Science Foundation of China (NNSFC) (11535002, 11705045), Natural Science Foundation of Hebei Province (A2020201002) and the youth top-notch talent support program of the Hebei Province

The minimal supersymmetric extension of the standard model (MSSM) is extended to the SSM, whose local gauge group is . To obtain the SSM, we add new superfields to the MSSM, namely, three Higgs singlets and right-handed neutrinos . The charge conjugate and parity (CP) violating effects are considered to study the lepton electric dipole moment (EDM) in the SSM. There are more CP violating phases in the SSM than in the standard model (SM). In this model, several new parameters are considered as CP violating phases; hence, there are new contributions to lepton EDMs. This is conducive to exploring the source of CP violation and probing new physics beyond the SM.

Gravitational waves from the phase transition in the B-LSSM

Based on the gauge symmetry group SU(3)C ⨂ SU(2)L ⨂ U(1)Y ⨂ U(1)B–L, the minimal supersymmetric extension of the SM with local B-L gauge symmetry(B-LSSM) has been introduced. In this model, we study the Higgs masses with the one-loop zero temperature effective potential corrections. Besides, the finite temperature effective potentials connected with two U(1)B-L Higgs singlets are deduced specifically. Then we can obtain the gravitational wave spectrums generated from the strong first-order phase transition. In the B-LSSM, with the fine-tuned parameter regions, we can obtain the strength parameter αθ ~ 0.14 and the ratio of speed to Hubble rate β/Hn ~ 5 at nucleation temperature, and then obtain observable gravitational wave signals. The gravitational wave signals can be as strong as h2ΩGW ~ 10–9, which may be detectable in the future experiments.

Next-to-leading-order corrections to the Higgs strahlung process from electron\u2013positron collisions in extended Higgs models

We present the cross section for e^{+}e^{-}rightarrow hZ with arbitrary sets of electron and Z boson polarizations at the full next-to-leading order in various extended Higgs models, such as the Higgs singlet model (HSM), the inert doublet model (IDM) and the two Higgs doublet model (2HDM). We systematically perform complete one-loop calculations to the helicity amplitudes in the on-shell renormalization scheme, and present the full analytic results as well as numerical evaluations. The deviation Delta R^{hZ} in the total cross section from its standard model (SM) prediction is comprehensively analyzed, and the differences among these models are discussed in details. We find that new physics effects appearing in the renormalized hZZ vertex almost govern the behavior of Delta R^{hZ}, and it takes a negative value in most cases. The possible size of Delta R^{hZ} reaches several percent under the theoretical and experimental bounds. We also analyze the deviation Delta R^{hZ}_{XY} in the total cross section times decay branching ratios of the discovered Higgs boson by utilizing the H-COUP program. It is found that the four types of 2HDMs can be discriminated by analyzing the correlation between Delta R^{hZ}_{tau tau } and Delta R^{hZ}_{bb} and those between Delta R^{hZ}_{tau tau } and Delta R^{hZ}_{cc}. Furthermore, the HSM and the IDM can be discriminated from the 2HDMs by measuring Delta R^{hZ}_{WW}. These signatures can be tested by precision measurements at future Higgs factories such as the International Linear Collider.

From Peccei Quinn symmetry to mass hierarchy problem

We propose a non-universal U(1) X gauge extension to the standard model (SM) and an additional Peccei–Quinn (PQ) global symmetry to study the mass hierarchy and strong CP problem. The scheme allows us to distinguish among fermion families and to generate the fermionic mass spectrum of particles of the SM. The symmetry breaking is performed by two scalar Higgs doublets and two scalar Higgs singlets, where one of these has the axion which turns out to be a candidate for cold dark matter. The exotic sector is composed by one up-like T and two down-like J 1,2 heavy quarks, two heavy charged leptons , one additional right-handed neutrino per family , and an invisible axion a. In addition, the large energy scale associated to the breaking of the PQ-symmetry gives masses to the right-handed neutrinos in such a way that the active neutrinos acquire eV-mass values due to the see-saw mechanism. On the other hand, from the non-linear effective Lagrangian, the flavour changing of the down quarks and charged leptons with the axion are considered.

The “96 GeV excess” at the LHC

The CMS collaboration reported an intriguing [Formula: see text] (local) excess at 96 GeV in the light Higgs-boson search in the diphoton decay mode. This mass coincides with a [Formula: see text] (local) excess in the [Formula: see text] final state at LEP. We briefly review the proposed combined interpretations for the two excesses. In more detail, we review the interpretation of this possible signal as the lightest Higgs boson in the 2 Higgs Doublet Model with an additional real Higgs singlet (N2HDM). We show which channels have the best prospects for the discovery of additional Higgs bosons at the upcoming Run 3 of the LHC.

The two-loop contributions to muon MDM in U(1)_X SSM

The MSSM is extended to the U(1)_X SSM, whose local gauge group is SU(3)_C times SU(2)_L times U(1)_Y times U(1)_X. To obtain the U(1)_X SSM, we add the new superfields to the MSSM, namely: three Higgs singlets {hat{eta }},~hat{{bar{eta }}},~{hat{S}} and right-handed neutrinos {hat{nu }}_i. It can give light neutrino tiny mass at the tree level through the seesaw mechanism. The study of the contribution of the two-loop diagrams to the MDM of muon under U(1)_X SSM provides the possibility for us to search for new physics. In the analytical calculation of the loop diagrams (one-loop and two-loop diagrams), the effective Lagrangian method is used to derive muon MDM. Here, the considered two-loop diagrams include Barr-Zee type diagrams and rainbow type two-loop diagrams, especially Z–Z rainbow two-loop diagram is taken into account. The obtained numerical results can reach 7.4times 10^{-10}, which can remedy the deviation between SM prediction and experimental data to some extent.

Uncovering the high-scale Higgs singlet model

The scalar singlet model extends the Standard Model with the addition of a new gauge singlet scalar. We reexamine the limits on the new scalar from oblique parameter fits and from a global fit to precision electroweak observables and present analytic expressions for our results. For the case when the new scalar is much heavier than the weak scale, we map the model onto the dimension-six Standard Model effective field theory and review the allowed parameter space from unitarity considerations and from the requirement that the electroweak minimum be stable. A global fit to precision electroweak data, along with LHC observables, is used to constrain the parameters of the high scale singlet model, and we determine the numerical effects of performing the matching at both tree level and one loop.

Anomaly-free chiral U(1)D and its scotogenic implication

We assume a dark $U_{D}$ symmetric hidden sector and explore its possible content such that neutrino mass and Dark Matter are generated through the scotogenic mechanism. The hidden sector is considered analogue to the Standard Model, namely the charge assignment of hidden fermions is chiral and anomaly-free. Moreover, $U_{D}$ is assumed broken by an only Higgs singlet that also generates masses to all hidden fermions, therefore the charge assignment is subjected to additional restriction. We search by computer program for charge assignments satisfying all these conditions, and identify the resulting minimal scotogenic models for Majorana neutrinos and Dirac neutrinos respectively in the sense of minimal number of messenger scalar involved. Particle spectrum, couplings, and phenomenologies of these minimal models are briefly discussed. DM is found multicomponent and always contains Dirac fermionic species.

Hierarchical quark and lepton masses with sequential U(1) gauge symmetry

Instead of right-handed neutrino singlets, the standard model is extended to include lepton triplets (Σ+,Σ0,Σ−). Each quark and lepton family may now transform under an anomaly-free U(1)X gauge symmetry, known already for many years. A new sequential application is presented, using just the one Higgs doublet of the standard model, together with two U(1)X Higgs singlets. The resulting structure has hierarchical quark and lepton masses, as well as a viable seesaw neutrino mass matrix.

Leading two-loop corrections to the Higgs boson self-couplings in models with extended scalar sectors

We compute the dominant two-loop corrections to the Higgs trilinear coupling lambda _{hhh} and to the Higgs quartic coupling lambda _{hhhh} in models with extended Higgs sectors, using the effective-potential approximation. We provide in this paper all necessary details about our calculations, and present general overline{{mathrm{MS}}} expressions for derivatives of the integrals appearing in the effective potential at two loops. We also consider three particular Beyond-the-Standard-Model (BSM) scenarios – namely a typical scenario of an Inert Doublet Model (IDM), and scenarios of a Two-Higgs-Doublet Model (2HDM) and of a Higgs Singlet Model (HSM) without scalar mixing – and we include all the necessary finite counterterms to obtain (in addition to overline{{mathrm{MS}}} results) on-shell scheme expressions for the corrections to the Higgs self-couplings. With these analytic results, we investigate the possible magnitude of two-loop BSM contributions to the Higgs self-couplings and the fate of the non-decoupling effects that are known to appear at one loop. We find that, at least as long as pertubative unitarity conditions are fulfilled, the size of two-loop corrections remains well below that of one-loop corrections. Typically, two-loop contributions to lambda _{hhh} amount to approximately 20% of those at one loop, implying that the non-decoupling effects observed at one loop are not significantly modified, but also meaning that higher-order corrections need to be taken into account for the future perspective of precise measurements of the Higgs trilinear coupling.