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.     

Effective action for the standard model with large Higgs mass

The covariant derivative expansion of the one-loop effective action is briefly reviewed, and applied to the problem of calculating the heavy Higgs effects in the standard Glashow-Weinberg-Salam model. All terms which grow with the Higgs mass M_H at one loop are found. The result of this calculation is used to find the dependence of the gauge boson mass ratio ϱ on M_H, and also to estimate the size of corrections to W and Z scattering theorems.     

Vertex functions for the three-particle interaction of the Higgs bosons <Emphasis Type="Italic">h</Emphasis><Superscript>0</Superscript> and <Emphasis Type="Italic">H</Emphasis><Superscript>0</Superscript> in the minimal supersymmetric standard model: One-loop analysis

Within the minimal supersymmetric standard model, two vertex functions for the three-particle interaction of the neutral Higgs bosons h⁰ and H⁰ are analyzed in the one-loop approximation with allowance for a complete set of one-loop diagrams. The analysis is performed in the c.m. frame under the assumption that one of the Higgs bosons is virtual. The results obtained in this way are compared with those that involve only leading corrections in the low-energy approximation. The vertex functions in question are presented graphically versus the mixing angle β and the energy \(\sqrt s\). It is shown that corrections to these vertex functions may be significant in some domain of the model-parameter space, so that they must be taken into account in performing a detailed analysis of experimental data and theoretical predictions. The possibility of experimentally observing the dependences under study is explored.     

Low-energy impact of a heavy Higgs boson sector

The effective theory which characterizes the low-energy sensitivity of the minimal Weinberg-Salam model to a heavy Higgs boson sector is shown to be the gauged SU(2)_L × U(1) non-linear θ model. This theory is the limit of the Weinberg-Salam model as the Higgs boson mass, M_H, is removed (M_H → ∞). Using the symmetry properties of the non-linear theory, along with a power-counting analysis, we are able to classify low-energy observables according to their sensitivity to the regulator (M_H). At one loop, the greatest sensitivity is a logarithmic dependence on the Higgs boson mass. The M_H dependent corrections to some specific, experimentally accessible observables are calculated, and other possible applications of this technique are discussed.     

Radiative corrections to Higgs production by e+e−→ZH in the Weinberg-Salam model

We present a complete analysis of the one-loop radiative corrections to the associated production of a Higgs boson (H) and a neutral vector boson (Z) in e⁺e^? annihilation up to energies and Higgs-boson masses of 1 TeV. In the region of interest for future experiments E ? 200 GeV (m_H ? 100 GeV) we find corrections of +25% which are essentially cancelled by soft-photon effects. The latter amount to ?31% for an electron counter resolution of 0.1.     

Production and two-photon decay of the MSSM scalar Higgs bosons at the LHC

We consider the production and two-photon decay of theCP-even Higgs bosons (h ⁰ andH ⁰) of the Minimal Supersymmetric Standard Model (MSSM) at the Large Hadron Collider. We study in detail the dependence of the cross section on various parameters of the MSSM, especially the dependence on the mixing effects in the squark sector due to the Higgs bilinear parameterμ and the soft supersymmetry breaking parameterA. We find that the cross section for the production of these Higgs bosons has a significant dependence on the parameters which determine the chiral mixing in the squark sector. The cross section times the two-photon branching ratio ofh ⁰ is of the order of 15–25 fb in much of the parameter space that remains after imposing the present experimental constraints. For theH ⁰ the two-photon branching ratio is only significant if theH ⁰ is light, but then the cross section times the branching ratio may exceed 200 fb. The QCD corrections due to quark loop contributions are known to increase the cross section by 50%. We find the dependence of the cross section on the gluon distribution function used to be rather insignificant.     

Solar neutrinos in models involving an extended Higgs sector

Neutrino oscillations in matter and in a magnetic field are investigated within models involving an extended Higgs sector. The left-right model containing a bidoublet and two triplets of Higgs fields (LRM) and the general two-Higgs-doublet model (GTHDM) are chosen by way of example. It is shown that the interaction of leptons with physical Higgs bosons can substantially change the pattern of oscillations in these models in relation to the predictions of the Standard Model (SM). Upper limits on the Yukawa coupling constants and on the Higgs boson masses are found in order to obtain maximum corrections to the SM solar-matter potential V ^SM. By using constraints on these parameters from the literature and those that are obtained here, it is possible to estimate corrections to V ^SM that come exclusively from charged Higgs bosons. The maximum value of these corrections is 40% of V ^SM within the LRM and 10% of V ^SM within the GTHDM. The entire body of information about the contributions of physical Higgs bosons to the solar-matter potential can be obtained by studying the Lorentz structure of the amplitudes for the reactions e ^? ν _l → e ^? ν _l′ at low energies.     

Full O(αew) electroweak corrections to e+e−→HHZ

We calculate the full $\text{O}\text{(α}{}_{\mathrm{<mtext>ew</mtext>}}\text{)}$ electroweak corrections to the Higgs pair production process e⁺e⁻→HHZ at an electron–positron linear collider in the standard model, and analyze the dependence of the Born cross section and the corrected cross section on the Higgs boson mass m_H and the c.m. energy $\text{s}$. To see the origin of some of the large corrections clearly, we calculate the QED and genuine weak corrections separately. The numerical results show that the corrections significantly suppress or enhance the Born cross section, depending on the values of m_H and $\text{s}$. For the c.m. energy $\text{s}\text{=500}$ GeV, which is the most favorable colliding energy for HHZ production with intermediate Higgs boson mass, the relative correction decreases from −5.3% to −11.5% as m_H increases from 100 to 150 GeV. For the range of the c.m. energy where the cross section is relatively large, the genuine weak relative correction is small, less than 5%.     

Simplified parametric scenarios of the Minimal Supersymmetric Standard Model after the discovery of the Higgs boson

Constraints on the parameter space of theMinimal Supersymmetric StandardModel (MSSM) that are imposed by the experimentally observed mass of the Higgs boson (m_H = 125 GeV) upon taking into account radiative corrections within an effective theory for the Higgs sector in the decoupling limit are examined. It is also shown that simplified approximations for radiative corrections in theMSSM Higgs sector could reduce, to a rather high degree of precision, the dimensionality of the multidimensionalMSSM parameter space to two.     

Effective gauge theory and the effect of heavy quarks in Higgs boson decays

A general framework is given for evaluating the contributions of as yet undiscovered heavy quarks to the gluonic decay rate of the Weinberg-Salam type Higgs boson. Since the Yukawa coupling of the Higgs boson to a quark pair is proportional to the quark mass, loop graphs involving heavy quarks have a non-vanishing effect on the gluonic decay width of the Higgs boson. This effect of heavy quarks with massesM _j(j=t,...) much greater than the Higgs boson massm _H is calculated in an effective gauge theory. The effects of two different kinds of large logarithms, lnM _j ² /μ m _h ² /μ ² are separated and summed up by the renormalization group method. It is found that the higher order QCD corrections are large and that the gluonic contribution to the hadronic decay width is significant if there are more than three generations. The Higgs decay width can therefore be used to probe the number of generations of heavy quarks.     

The couplings of Higgs bosons to two vector mesons in multi-Higgs models

We calculate the (induced) couplings of neutral Higgs scalars to two photons and to one photon and one Z-boson in a two-doublet model. We give the generalization to more scalar multiplets and investigate the case when Higgs → γγ is a substantial mode. Then we give conditions for the existence of a W⁺ ZH⁺ coupling (H⁺ is a charged scalar). Some aspects of non-linear gauges are elaborated on.     

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).     

Electroweak radiative corrections to the top quark decay

The top quark, once produced, should be an important window to the electroweak symmetry breaking sector. We compute electroweak radiative corrections to the decay processt→b+W ⁺ in order to extract information on the Higgs sector and to fix the background in searches for a possible new physics contribution. The large Yukawa coupling of the top quark induces a new form factor through vertex corrections and causes discrepancy from the tree-level longitudinalW-boson production fraction, but the effect is of order 1% or less form _H<1 TeV.     

Renormalization group estimate of the hadronic decay width of the Higgs boson

The total hadronic decay width of the Weinberg-Salam type Higgs boson is estimated in QCD for the Higgs boson mass much larger than the ordinary hadronic mass scale, by use of the operator product expansion and renormalization group equation. We give an explicit formula for the decay width in terms of quark masses including strong interaction corrections up to the next-to-leading order. A numerical analysis of the hadronic decay width of the Higgs boson is made in the six-quark model. The next-to-leading order correction is found to be significant, e.g., 30-20% of the leading term for m_H of oue interest, m_H ? 1 TeV. Application of our scheme to the decay rates of heavy Higgs bosons of other types is also discussed.     

The intermediate-massL M Higgs boson at the NLC: reducible and irreducible backgrounds to the Bjorken production channel

Both the reducible and irreducible backgrounds to the Higgs production channele ⁺ e ^???H ⁰ Z ⁰ at a Next Linear Collider (NLC) are studied, for the Standard Model (L M) Higgs boson in the intermediate-mass range. A phenomenological analysis that does not exploit any form of tagging on the Higgs decay products is assumed.     

The intermediate-massL M Higgs boson at the NLC: reducible and irreducible backgrounds to the Bjorken production channel

Both the reducible and irreducible backgrounds to the Higgs production channele ⁺ e ^?→H ⁰ Z ⁰ at a Next Linear Collider (NLC) are studied, for the Standard Model (L M) Higgs boson in the intermediate-mass range. A phenomenological analysis that does not exploit any form of tagging on the Higgs decay products is assumed.     

Radiative corrections to helicity amplitudes forW-pair production ine + e−-annihilation

Radiative corrections toW pair production ine ⁺ e^?-annihilation are investigated. In an earlier work we discussed only the weak corrections to this process. Here we present the complete calculation including QED corrections. Full agreement with other authors is achieved. We use the helicity formalism for the projection of theS-matrix into invariant amplitudes and study the dependence of cross sections on the Higgs and top masses. Effects due to the choice of the renormalization scheme are considered.     

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.     

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.     

Higgs detection via Z0 polarisation

It is demonstrated that if one determines the polarisation of the Z⁰ final states from pp → Z⁰Z⁰ → charged leptons, then one can reliably detect the presence of a Higgs boson in the range 300 GeV < m_H < 1 TeV at the SSC. This is in contrast to other methods for Higgs detection which are susceptible to QCD backgrounds, severe cuts, or uncertainties in the Z⁰ continuum. For one year's running at the nominal SSC luminosity of 10³³ cm⁻² s⁻¹ and energy 40 TeV there are sufficient numbers of such events to perform the straightforward analysis.