Mass bounds of the lightest CP-even Higgs boson in the two-Higgs-doublet model

The upper and the lower bounds of the lightest CP-even Higgs-boson mass (m_h) are discussed in the two-Higgs-doublet model (2HDM) with a softly-broken discrete symmetry. They are obtained as a function of a cut-off scale Λ (≤10¹⁹ GeV) by imposing the conditions in which the running coupling constants neither blow up nor fall down below Λ. In comparison with the standard model (SM), although the upper bound does not change very much, the lower bound is considerably reduced. In the decoupling regime where only one Higgs boson (h) becomes much lighter than the others, the lower bound is given, for example, by about 100 GeV for Λ=10¹⁹ GeV and m_t=175 GeV, which is smaller by about 40 GeV than the corresponding lower bound in the SM. In generic cases, m_h is no longer bounded from below by these conditions. If we consider the b→sγ constraint, small values of m_h are excluded in Model II of the 2HDM.     

LEP Higgs boson searches beyond the standard model and minimum supersymmetric standard model

Ever since the center-of-mass energy was increased in 1995 above the Zℴ resonance, the four LEP experiments (ALEPH, DELPHI, OPAL and L3) have renewed their effort to search for the Higgs boson. Data taking ended in the year 2000 with about 130 pb⁻¹ of data collected per experiment above 206 GeV ine ⁺ e ⁻¹ collisions but the data analysis is still very active. Most recently, the wealth of theoretical models and predictions has stimulated new analyses and model interpretations which go beyond the standard model and minimal supersymmetric standard model. These include the searches for charged Higgs bosons, models with two Higgs field doublets, searches for ‘fermiophobic’ Higgs decay, invisible Higgs boson decays, decay-mode independent searches, and limits on Yukawa and anomalous Higgs couplings. I review the searches done by the four LEP experiments and present the LEP combined results when they exist.     

Upper limit to the lightest Higgs mass in supersymmetric models

Consider all models in which the effective low-energy theory has an SU(3) × SU(2) × U(1) gauge group, softly or spontaneously broken supersymmetry, and Higgs doublets. Even though, in general, mass terms in such models are arbitrary (thus “ino” masses can be pushed up to higher and higher values), one can derive mass relations between ordinary Higgs particles. The most crucial relation gives an upper bound of 93 GeV on the mass of the lightest Higgs scalar. We discuss these relations and calculate radiative corrections to them. It is shown that the upper bound can not exceed 95 GeV, and the lower limit to the mass of charged scalar is 78 GeV. Corrections to other relations are also discussed. These relations may provide the first definitive test of low-energy supersymmetry.     

Precise prediction for the mass of the lightest Higgs boson in the MSSM

The leading diagrammatic two-loop corrections are incorporated into the prediction for the mass of the lightest Higgs boson, m_h, in the Minimal Supersymmetric Standard Model (MSSM). The results, containing the complete diagrammatic one-loop corrections, the new two-loop result and refinement terms incorporating leading electroweak two-loop and higher-order QCD contributions, are discussed and compared with results obtained by renormalization group calculations. Good agreement is found in the case of vanishing mixing in the scalar quark sector, while sizable deviations occur if squark mixing is taken into account.     

Yukawa coupling quantum corrections to the self-couplings of the lightest MSSM Higgs boson

A detailed analysis of the top-quark/squark quantum corrections to the lightest CP-even Higgs boson self-couplings is presented in the MSSM. By considering the leading one-loop Yukawa-coupling contributions of , we discuss the decoupling behavior of these corrections when the top squarks are heavy compared to the electroweak scale. As shown analytically and numerically, the large corrections can almost completely be absorbed into the -boson mass. Our conclusion is that the self-couplings remain similar to the coupling of the SM Higgs boson for the heavy top-squark sector. Received: 15 November 2001 / Published online: 25 January 2002     

Radiative corrections to Higgs boson masses in supersymmetric models

The effect of radiative corrections on the Higgs masses and couplings in supersymmetric models is summarized. Radiative corrections in both the minimal and nonminimal models are discussed. It is pointed out that large singlet Higgs vacuum expectation values are screened out from the radiative corrections to the lightest Higgs mass in nonminimal models. In supersymmetric models the crucial mass limit for the Higgs search may be around 150 GeV.     

Radiative corrections to Higgs boson masses in supersymmetric models

The effect of radiative corrections on the Higgs masses and couplings in supersymmetric models is summarized. Radiative corrections in both the minimal and nonminimal models are discussed. It is pointed out that large singlet Higgs vacuum expectation values are screened out from the radiative corrections to the lightest Higgs mass in nonminimal models. In supersymmetric models the crucial mass limit for the Higgs search may be around 150 GeV.     

The search for a supersymmetric Higgs boson at LEP

It is shown that LEP can set a lower bound on the mass of the lightest supersymmetric Higgs boson (H₂⁰) only if both processes Z⁰→H₂⁰μ⁺μ⁻ and Z⁰→H₂⁰H₃⁰ (where H₃⁰ is an extra supersymmetric Higgs) are simultaneously considered.     

Triviality bound on lightest Higgs mass in next to minimal supersymmetric model

We study the implication of triviality on Higgs sector in next to minimal supersymmetric model (NMSSM) using variational field theory. It is shown that the mass of the lightest Higgs boson in NMSSM has an upper bound ∼10M _W which is of the same order as that in the standard model.     

Electroweak Higgs boson production in the standard model effective field theory beyond leading order in QCD

We study the impact of dimension-six operators of the standard model effective field theory relevant for vector-boson fusion and associated Higgs boson production at the LHC. We present predictions at the next-to-leading order accuracy in QCD that include matching to parton showers and that rely on fully automated simulations. We show the importance of the subsequent reduction of the theoretical uncertainties in improving the possible discrimination between effective field theory and standard model results, and we demonstrate that the range of the Wilson coefficient values allowed by a global fit to LEP and LHC Run I data can be further constrained by LHC Run II future results.     

Higgs boson properties in the Standard Model and its supersymmetric extensions

We review the realization of the Brout–Englert–Higgs mechanism in the electroweak theory and describe the experimental and theoretical constraints on the mass of the single Higgs boson expected in the minimal Standard Model. We also discuss the couplings of this Higgs boson and its possible decay modes as functions of its unknown mass. We then review the structure of the Higgs sector in the minimal supersymmetric extension of the Standard Model (MSSM), noting the importance of loop corrections to the masses of its five physical Higgs bosons. Finally, we discuss some non-minimal models. To cite this article: J. Ellis et al., C. R. Physique 8 (2007).     

The coupling of the lightest SUSY Higgs boson to two photons in the decoupling regime

We analyze the contribution of the SUSY particles to the coupling of the lightest Higgs boson to two photons in supersymmetric theories. We discuss to what extent these contributions can be large enough to allow for a discrimination between the lightest SUSY and the standard Higgs particles in the decoupling limit where all other Higgs bosons are very heavy and no supersymmetric particle has been discovered at future colliders. We find that only chargino and top squark loops can generate a sizeable difference between the standard and the SUSY Higgs-photon couplings. For masses above 250 GeV, the effect of chargino loops on the two-photon width is however smaller than ≈ 10% in the entire SUSY parameter space. Top squarks heavier than 250 GeV can induce deviations larger than 10% only if their couplings to the Higgs boson are large. Since top squark contributions can be sizeable, we derive the two-loop QCD correction to squark loops and show that they are well under control.     

The equivalent vector boson approximation for intermediate mass Higgs boson production

We consider the equivalent vector boson approximation (EVBA) for the processqq→qqWW→qqH andqq→qqZZ→qqH. It is shown that the contributions σT and σL, of the transversely and longitudinally polarized vector bosonsV respectively, are comparable with each other for intermediate values ofm _H viz. 0.3 TeV to 0.6 TeV. σT can be as large as 1.5–2 times σL in this mass range. As a result the leading EVBA for σ=σL+σT overestimates the exact total cross-section by a factor, upto 2–3 even, at high energies. σT is negligible with respect to the leading contribution σL only form _H≧0.6 TeV, where EVBA is correct within 15–20%. Further the effect of the corrections to EVBA, which are naively of nonleading order, on these conclusions in the framework of the EVBA is discussed.     

Study of diphoton decays of the lightest scalar Higgs boson in the Next-to-Minimal Supersymmetric Standard Model

The CMS and ATLAS experiments at the LHC have announced the discovery of a Higgs boson with mass at approximately 125 GeV/c² in the search for the Standard Model Higgs boson via, notably, the γγ and ZZ to four leptons final states. Considering the recent results of the Higgs boson searches from the LHC, we study the lightest scalar Higgs boson h₁ in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson h₂ to be the observed to the 125 GeV/c² state. We perform a scan over the relevant NMSSM parameter space that is favoured by low fine-tuning considerations. Moreover, we also take the experimental constraints from direct searches, B-physics observables, relic density, and anomalous magnetic moment of the muon measurements, as well as the theoretical considerations, into account in our specific scan. We find that the signal rate in the two-photon final state for the NMSSM Higgs boson h₁ with the mass range from about 80 GeV/c² to about 122 GeV/c² can be enhanced by a factor of up to 3.5 when the Higgs boson h₂ is required to be compatible with the excess from latest LHC results. This motivates the extension of the search at the LHC for the Higgs boson h₁ in the diphoton final state down to masses of 80 GeV/c², particularly with the upcoming proton-proton collision data to be taken at center-of-mass energies of 13-14 TeV.