Heavy SUSY Higgs bosons at e + e − linear colliders

The production mechanisms and decay modes of the heavy neutral and charged Higgs bosons in the Minimal Supersymmetric Standard Model are investigated at future e ⁺ e ^? colliders in the TeV energy regime. We generate supersymmetric particle spectra by requiring the MSSM Higgs potential to produce correct radiative electroweak symmetry breaking, and we assume a common scalar mass m₀, gaugino mass m_1/2 and trilinear coupling A, as well as gauge and Yukawa coupling unification at the Grand Unification scale. Particular emphasis is put on the low tan β solution in this scenario where decays of the Higgs bosons to Standard Model particles compete with decays to supersymmetric charginos/neutralinos as well as sfermions. In the high tan β case, the supersymmetric spectrum is either too heavy or the supersymmetric decay modes are suppressed, since the Higgs bosons decay almost exclusively into b and τ pairs. The main production mechanisms for the heavy Higgs particles are the associated AH production and H ⁺H^? pair production with cross sections of the order of a few fb.     

Loop induced flavor changing neutral decays of the top quark in a general two-Higgs-doublet model

Decays of the top quark induced by flavor changing neutral currents (FCNC) are known to be extremely rare events within the Standard Model. This is so not only for the decay modes into gauge bosons, but most notably in the case of the Higgs channels, e.g., t→H_SM+c, with a branching fraction of 10⁻¹³ at most. Therefore, detection of FCNC top quark decays in a future high-energy, and high-luminosity, machine like the LHC or the LC would be an indisputable signal of new physics. In this paper we show that within the simplest extension of the SM, namely the general two-Higgs-doublet model, the FCNC top quark decays into Higgs bosons, t→(h⁰,H⁰,A⁰)+c, can be the most favored FCNC modes — comparable or even more efficient than the gluon channel t→g+c. In both cases the optimal results are obtained for Type II models. However, only the Higgs channels can have rates reaching the detectable level (10⁻⁵), with a maximum of order 10⁻⁴ which is compatible with the charged Higgs bounds from radiative B-meson decays. We compare with the previous results obtained in the Higgs sector of the MSSM.     

Radiative corrections to the vector boson-charged-Higgs-boson vertex

Radiative corrections to the gauge bosoncharged Higgs vertex are calculated to one loop, and are applied to the decayZ→H ⁺ H ^?. Naively, one expects the corrections to be quite large due to the contribution from fermion loops. If this is the case one could hope to extract some information on the Yukawa couplings in the charged Higgs sector.     

Can one test technicolour?

We estimate the couplings to ordinary particles of the lightest bound states in technicolour theories and discuss the resulting phenomenology. We compute their couplings to light gauge bosons through axial anomalies and also estimate their non-anomalous couplings at low energies. We estimate their couplings to fermions under the general simplifying assumption that each fermion acquires its mass from a unique technifermion condensate (“monophagy”), in which case they are naturally flavour conserving and relatively well-defined. We find that the classic Higgs search experiments (ttoponium → H⁰ + γ, e⁺e^? → H⁺H^?, e⁺e^? → Z⁰ + H⁰) enable one to make a decisive discrimination between elementary and composite models of spontaneous symmetry breaking. We also emphasize the interest of improving experimental limits on K_L⁰ → μe in the context of dynamical symmetry breaking models.     

Non-standard Higgs bosons inSU(2)×U(1) radiative corrections

The 1-loop renormalization of theSU(2)×U(1) electroweak gauge theory with two Higgs doublets is performed in the on-shell scheme with finite self energies and vertices. Assuming different vacuum expectation values for the scalar doublets, which yield enhanced Yukawa couplings to fermions, we calculate the effects of the additional Higgs bosons in the radiative corrections to the leptonic processes:μ-decay,v _μ e-scattering, ande ⁺ e ^?→μ ⁺ μ ^?,τ ⁺ τ ^? with longitudinal polarization at PETRA and LEP/SLC energies. It is found that large effects occur in theM _W ?M _Z mass relation, the determination of sin² θ _w from \(\sigma (v_\mu e)/\sigma (\bar v_\mu e)\) and thee ⁺ e ^? forward-backward and polarization asymmetries, if either the charged Higgs or the additional neutral scalar/pseudoscalar are heavy. Enhancement effects and effects of light neutral bosons can better be observed in thee ⁺ e ^?→τ ⁺ τ ^? integrated cross section.     

Charged Higgs production at hadron colliders

We study the production and decay of charged Higgs bosons,H ^±, at TEVATRON and SSC energies as a function of the top massm _t and theH ^± massm _H . We give the cross sections for events arising from bothH ^±→τν andtb decays, together with those of the competing background processes. In particular, form _t >m _H we studyH ^± W ^? andW ⁺ W ^? production and thet→bτν decay.     

Light charged Higgs scalars at high-energy e+e− colliders

We study the prospects for detecting light charged Higgs scalars (H^±) at future e⁺e⁻ colliders. Various two-Higgs-doublet models (2HDM) and a general multi-Higgs-doublet model (MHDM) are considered, all of which may contain a H^± in the discovery range of LEP2. The potentially troublesome cases of M_H^± ∼ M_W and M_H^± ∼ M_Z are discussed, as well as ways of distinguishing the different models.     

Anomalous magnetic moment of the muon in the left-right model

The effect of Higgs bosons on the anomalous magnetic moment of the muon is considered within the model that is based on the SU(2)_L×SU(2)_R×U(1)_B–L gauge group and which involves a bidoublet and two triplets of Higgs fields (left-right model). For the Yukawa coupling constants and the masses of Higgs bosons, the regions are found where the model leads to agreement with experimental results obtained at the Brookhaven National Laboratory (BNL) for the anomalous magnetic moment of the muon. In order to explore corollaries from the constraints obtained for the parameters of the Higgs sector, the processes e⁺e^? → μ⁺μ^?, τ⁺τ^? and μ⁺μ^? → μ⁺μ^?, τ⁺τ^? are considered both within the left-right model and within the model involving two Higgs doublets (two-Higgs-doublet model). It is shown that, if the mass of the lightest neutral Higgs boson does indeed lie in the range 3.1–10 GeV, as is inferred from the condition requiring the consistency of the two-Higgs-doublet model with the data of the BNL experiment, this Higgs boson may be observed as a resonance peak at currently operating e⁺e^? colliders (VEPP-4M, CESR, KEKB, PEP-II, and SLC). In order to implement this program, however, it is necessary to reduce considerably the scatter of energy in the e⁺ and e^? beams used, since the decay width of the lightest neutral Higgs boson is extremely small at such mass values. It is demonstrated that, in the case of the left-right model, for which the mass of the lightest neutral Higgs boson is not less than 115 GeV, the resonance peak associated with it may be detected at a muon collider.     

Higgs bosons and neutrinos in the left-right model

The left-right asymmetric model featuring the bidoublet and two triplets of Higgs fields is investigated. It was established that, from an analysis of the reaction l ^?γ → W ^?ν_l, it is possible to deduce not only information about the properties of the singly charged Higgs bosons $\tilde \delta ^{( - )} $ and h ^(?) but also an answer to the question of whether the neutrino is a Majorana or a Dirac particle. The processes $f_i \bar f_j \to \Delta _1^{( - - )} \tilde \delta ^{( + )} $ and e^?μ^? → Δ _1,2 ^(—) γ leading to the production of doubly charged Higgs bosons are investigated. It is shown that information about the properties of singly charged Higgs bosons can also be obtained by studying the ultrahighenergy cosmic neutrinos from the reaction e ^?ν _e →μ^?ν_μ.     

Initial-final state interference ine + e −→H μ + μ −

Here we take the processe ⁺ e ^?→H μ ⁺ μ ^? and compute a special class of one-loop QED corrections, namely the interference effects between the initial and final state radiation (interference radiation for short). This analysis is restricted to soft bremsstrahlung. The possibility of the Higgs boson detection at LEP-II is our major motivation, and the numerical values used both for the Higgs boson mass and the center of mass energy are a direct consequence of this.     

Higgs boson physics in the s-channel at μ+μ− colliders

Techniques and strategies for discovering and measuring the properties of Higgs bosons via s-channel production at a μ⁺μ⁻ collider, and the associated requirements for the machine and detector, are discussed in detail. The unique feature of s-channel production is that, with good energy resolution, the mass, total width and partial widths of a Higgs boson can be directly measured with remarkable accuracy in most cases. For the expected machine parameters and luminosity the standard model (SM) Higgs boson h_SM, with mass ≲ 2m_W, the light h⁰ of the minimal supersymmetric standard model (MSSM), and the heavier MSSM Higgs bosons (the CP-odd A⁰ and the CP-even H⁰) can all be studied in the s-channel, with the heavier states accessible up to the maximal √s over a large fraction of the MSSM parameter space. In addition, it may be possible to discover the A⁰ and H⁰ by running the collider at full energy and observing excess events in the bremsstrahlung tail at lower energy. The integrated luminosity, beam resolution and machine/detector features required to distinguish between the h_SM and h⁰ are delineated.     

Search for charged Higgs,scalar tau's and a test of technicolor models

We have used our measurements of final states from e⁺e^? containing an isolated muon and a hadronic or electron shower to search for new spin 0 charged particles. We exclude (95% CL) a supersymmetric partner of the τ with a mass less than 14 GeV/c². We obtain upper limits on the branching ratio to τv_τ for charged Higgs particles or technipions with masses up to 14 GeV/c². This disagrees with some technicolor model predictions.     

Higgs radiation off top quarks in high-energye + e − colliders

Higgs particles can be radiated off heavy top quarks which will be produced copiously in high energye ⁺ e ^? colliders. This process can be used to measure the Higgs-top quark coupling. We present the cross section for the production of Higgs bosons in the Standard Model. In addition we have studied the production of neutral and charged Higgs particles in association with heavy fermions in the Minimal Supersymmetric Standard Model.     

Energy spectra and energy correlations in the decayH→ZZ→μ+μ−μ+μ−

It is shown that in the sequential decay $H \to ZZ \to (f_1 \bar f_1 ) + (f_2 \bar f_2 )$ , the energy distribution of the final state particles provides a simple and powerful test of theHZZ vertex. For a standard Higgs boson, the energy spectrum of any final fermion, in the rest frame ofH, is predicted to be dΓ/dx～1+β⁴?2(x?1)², with $\beta = \sqrt {1 - 4m_Z^2 /m_H^2 } $ and 1?β≤x=4E/m _H ≤1+β. By contrast, the spectrum for a pseudoscalar Higgs is dΓ/dx～β²+(x?1)². There are characteristic energy correlations betweenf ₁ andf ₂ and betweenf ₁ andf ₂. These considerations are applied to the “gold-plated” reactionH→ZZ→μ⁺μ^?μ⁺μ^?, including possible effects ofCP-violation in theHZZ coupling. Our formalism also yields the energy spectra and correlations of leptons in the decay $H \to W^ + W^ - \to l^ + v_l l^ - \bar v_l $ .     

The Higgs-photon-Z boson coupling revisited

We analyze the coupling of CP-even and CP-odd Higgs bosons to a photon and a Z boson in extensions, of the Standard Model. In particular, we study in detail the effect of charged Higgs bosons in two-Higgs doublet models;. and the contribution of SUSY particle loops in the minimal supersymmetric extension of the Standard Model: The Higgs-γZ coupling can be measured in the decayZ → γ+Higgs ate ⁺ e ^? colliders running on theZ resonance, or in the reverse process Higgs →Zγ with the Higgs boson produced at LHC. We show that a measurement of this coupling with a precision at the percent level, which could be the case at futuree ⁺ e ^? colliders, would allow to distinguish between the lightest SUSY and standard Higgs bosons in large areas of the parameter space.     

Charged Higgs boson in the economical 3-3-1 model

The SU(3) _C ⊗ SU(3) _L ⊗ U(1) _X gauge model with two Higgs triplets (the economical 3-3-1 model) is presented. The minimal Higgs potential is considered in detail, and new Higgs bosons with the mass proportional to the bilepton mass are predicted. In the effective approximation, the charged Higgs bosons H ₂ ^± are scalar bileptons, while the neutral scalar bosons H ⁰ and H ₁ ⁰ do not carry a lepton number. The couplings of the charged Higgs bosons to leptons and quarks are given. We show that Yukawa couplings of H ₂ ^± to ordinary leptons and quarks are lepton-number violating. The pair production of H ₂ ^± at high-energy e ⁺ e ⁻ colliders with the polarization of the e ⁺, e ⁻ beams is studied in detail. A numerical evaluation shows that, if the Higgs mass is not too heavy, then the reaction can give an observable cross section in future colliders at a high degree of polarization. The reaction e ⁺ e ⁻ → H ₂ ^± W ^∓ is also examined. We show that the production cross sections of H ₂ ^± W ^∓ are very small, much below the pair production of H ₂ ^± , and, therefore, the associated production of H ₂ ^± and W ^∓ is, in general, not expected to lead to easily observable signals in the e ⁺ e ⁻ annihilation. The text was submitted by the authors in English.     

The higgs boson mass from precision electroweak data

We present a new global fit to precision electroweak data, including new low- and high-energy data and analyzing the radiative corrections arising from the minimal symmetry breaking sectors of the Standard Model (SM) and its supersymmetric extension (MSSM). It is shown that present data favor a Higgs mass ofO(M _z):M _H=76 _?50 ⁺¹⁵² GeV. We confront our analysis with (meta) stability and perturbative bounds on the SM Higgs mass, and the theoretical upper bound on the MSSM Higgs mass. Present data do not discriminate significantly between the SM and MSSM Higgs mass ranges. We comment in passing on the sensitivity of the Higgs mass determination to the values ofα(M _z) andα _s(M _z).     

Production on heavy Higgs bosons ate + e −-colliders

The production of Higgs bosons in the mass range of 200 GeV/c²<M _H <1TeV/c ² ate ⁺ e ^? super colliders is studied. We consider the possibilities to detect Higgs bosons via their decays into vector boson pairs. Single particle distributions of vektor bosons arising from this decay are compared with background reactions. We find, that the signal of Higgs bosons with masses up to 60- GeV/c² should be visible over the background already at \(\sqrt s = 1\) TeV, provided that the vektor bosons can be identified via their hadronic decay modes.     

Four weak gauge boson production at photon linear collider and heavy Higgs signal

We study the signals and backgrounds for a heavy Higgs boson in the processes γγ → WWWW, γ → WWZZ at the proton linear collider. The results are based on the complete tree-level SM calculation for these reactions. We show that the invariant mass spectrum of central WW, ZZ pairs is sensitive to the signal from Higgs boson with a mass up to 1 TeV linear collider for integrated luminosity of 300 fb⁻¹. At 1.5 TeV PLC Higgs boson with a mass up to 700 GeV can be studied. The nonresonant longitudinal gauge boson scattering (m_H = ∞) can be detected in photon-photon collisions at e⁺e⁻ center-of-mass energy of 3 TeV.     

Virtual effects of Higgs particles

The possibility of observing Higgs particles through virtual effects is considered in detail for a general gauge theory. The effect of charged Higgs particles on low-energy weak interaction processes, like muon decay, tau decay, nuclear beta decay, pion decay, and some higher-order processes is analyzed. The effect of flavor-changing neutral Higgs particles on rare decay modes of the muon and kaon, μe conversion, K^o-$\text{K}$^o and D^o-$\text{D}$^o mixing is also studied. We discuss constraints on possible extensions of the Weinberg-Salam model and experiments sensitive to their Higgs particles. In particular, we analyze the neutral Higgs which couple to fermions in the minimal SU(2)_L×SU(2)_R×U(1) model and find that they probably have mass greater than 100 GeV.