Higgs-boson production together with neutrino pair at e+e− colliders

The cross section for production of supersymmetric neutral Higgs boson in association with a neutrino-antineutrino muon pair in e⁺e^? annihilation are calculated, i.e. $e^ + e^ - \to \nu _\mu \bar \nu _\mu H_i^0 $ via different propagators.     

Quark-antiquark pair production via γW fusion at high energye + e − colliders

We calculate numerically the cross section for the process \(e^ + e^ - \to ve^ + Q_d \bar Q_u \) using the Weizsäcker-Williams approximation for the virtual photon. This process is a possible background for the detection of an “intermediate” Higgs via its decay into \(Q\bar Q\) pairs. The comparison with the signal allows us to conclude that actually it is not a problem for the Higgs search at high energye ⁺ e ^? colliders.     

Zinos and scalar muon production at e+e− colliders

Single scalar muon production is examined in detail which results in a final state particularly favourable for detection: two strongly acollinear muons plus large missing energy. Cross sections, missing energy and angular distributions are given. A strong dependence on the zino total width, common to all single production channel, is found.     

SUSY-QCD corrections to scalar quark pair production in e+e− annihilation

We calculate the supersymmetric O(α_s) QCD corrections to the cross section e⁺e⁻ → q̃_iq̃_j (i, j = 1,2) within the Minimal Supersymmetric Standard Model. We pay particular attention to the case of the left-right squark mixing and to the renormalization of the mixing angle. The corrections due to gluino exchange turn out to be smaller than those due to gluon exchange, but they can be significant at higher energies, even for a gluino mass of a few hundred GeV.     

Radiative corrections for associatedZH production at futuree + e − colliders

The \(ZHf\bar f\) four-point function is calculated in the one-loop approximation of the Standard Model and full analytic results are presented. The loop contributions due to both light and new heavy fermions are inspected in detail. The dominant mechanisms of Higgs-boson production from fermions are compared. The effect of radiative corrections on the cross section of \(f\bar f \to ZH\) including bremsstrahlung is studied. The spectrum of hard bremsstrahlung is integrated analytically. The implications for Higgs-boson searches at futuree ⁺ e ^? colliders in the energy range 200 \(200GeV \le \sqrt s \le 1.5TeV\) , which includes both LEP 2 and the Next Linear Collider, are analyzed. ForM _H <2m _t weak corrections in the modified on-mass-shell scheme are generally negative and feebly vary withM _H , while forM _H >2m _t , they strongly increase withM _H and may take large positive values. Electromagnetic corrections dramatically reduce the cross section close to theZH-production threshold, while they may considerably enhance it far above this threshold.     

The production ofW + W − pairs in proton-antiproton colliders

We present the predictions of the Glashow-Weinberg-Salam [1] (GWS) model for the total cross-section and the angular and invariantmass differential cross sections for the reaction \(p\bar p \to W^ + W^ - X\) . We contrast these GWS predictions with those obtained by varying the anomalous magnetic moment of theW(κ), the analogue for theZWW coupling (κ _z ) and the relative strength of the γWW andZWW couplings (ω) from their GWS values. We find that changes in these parameters produce significant changes in both the total cross section and the angular and invariant mass differential cross sections. We also present the angular distribution of the decay leptons (W ⁺→/+v _l) and find in all cases it closely mirrors theW ⁺ angular distribution. We have given the intermediate results for the dominant quark subprocesses \((u\bar u \to W^ + W^ - ,d\bar d \to W^ + W^ - )\) .     

W+W−γ production in e+e− annihilation in the TeV region

The reaction e⁺e⁻→γW⁺W⁻ has been studied at TeV energies as a possible background to Higgs production. Our results differ significantly from previous estimates and show that the ratio signal/background can be kept reasonably large.     

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.     

Vector boson pair production in e−e− collisions with polarized beams

The W-boson pair production in e⁻e⁻ collisions with polarized beams is investigated. The helicity amplitudes are derived for general couplings and the conditions for a good high-energy behaviour of the cross-section are given. The results are applied to the heavy vector boson production in the context of the left-right symmetric model. The Ward identities and the equivalence theorem are also discussed.     

Aspects of two-photon physics at lineare + e − colliders

We discuss various reactions at futuree ⁺ e ^– and colliders involving real (beamstrahlung or backscattered laser) or quasi-real (bremsstrahlung) photons in the initial state and hadrons in the final state. The production of two central jets with large transverse momentump _T is described in some detail; we give distributions for the rapidity andp _T of the jets as well as the di-jet invariant mass, and discuss the relative importance of various initial state configurations and the uncertainties that arise from the at present rather poor knowledge of the parton content of the photon. We also present results for mono-jet production where one jet goes down a beam pipe, for the production of charm, bottom and top quarks, and for single production ofW andZ bosons. Where appropriate, the two-photon processes are compared with annihilation reactions leading to similar final states. We also argue that the behaviour of the total inelastic cross section at high energies will probably have little impact on the severity of background problems caused by soft and semi-hard (minijet) two-photon reactions. We find very large differences in cross sections for all two-photon processes between existing desings for futuree ⁺ e ^– colliders, due to the different beamstrahlung spectra; in particular, both designs with 1 and 1 events per bunch crossing exist. The number of hadronic two-photon events is expected to rise quickly with the beam energy. Hadronic backgrounds will be even worse if thee ⁺ e ^– collider is converted into a collider.     

Inclusive one- and two-jet cross sections in γγ reactions at e+e− colliders

We have calculated inclusive one- and two jet production in photon-photon collisions superimposing direct, single-resolved and double-resolved cross sections for center of mass energies of the LEP1, LEP2 and NLC range. The direct and single-resolved cross sections are calculated up to next-to-leading order. The double-resolved two-jet cross section is calculated only in LO with a k factor estimated from the NLO one jet cross section. Various differential cross sections as functions of transverse momenta and rapidities of the jets are evaluated.     

Anomalous three-boson coupling constants in the single production of W bosons at a future e + e − linear collider

The question of whether constraints on the anomalous parameters of WWγ and WWZ three-boson interactions can be deduced from an analysis of data on the reaction e ⁺ e ^? → W ^? e ⁺ ν that are expected to come from a future $\sqrt s = 500 - GeVe^ + e^ - $ linear collider of integrated luminosity of L=50, 100, or 500 fb^? is discussed. An analysis of relevant differential distributionns reveals that, in contrast to pair W-boson production, the reaction mentioned immediately above is highly sensitive to the parameter λ _Z and that the resulting constraints can be viewed as those that supplement the constraints that follow from data on e ⁺ e ^?→W ⁺ W ^?. For the experiment being discussed, two possible implementations of a detector are considered that correspond to the kinematical regions |cos $\left| {\cos \theta _{e^ + } } \right| \leqslant \cos 7^\circ $ and $\left| {\cos \theta _{e^ + } } \right| \leqslant \cos 1.5^\circ $ . It is indicated that the region of small positron-scattering angles is of importance for improving the sensitivity of the process. In setting constraints on the anomalous parameters, the SEWS scenario for anomalous boson coupling constants, where interactions responsible for electroweak-symmetry breaking are strongly coupled, is examined along with the case of the most general parametrization of the WWγ(Z) three-boson vertices.     

Effective field theory analysis of new physics in e + e −→W + W − at a linear collider

The effective Lagrangian with scalar and vector resonances that might result from new strong physics beyond the SM is formulated and studied. In particular, the scalar resonance representing the recently discovered 125-GeV boson is complemented with the SU(2) _L+R triplet of hypothetical vector resonances. Motivated by experimental and theoretical considerations, the vector resonance is allowed to couple directly to the third quark generation only. The coupling is chiral-dependent and the interaction of the right top quark can differ from that of the right bottom quark. To estimate the applicability range of the effective Lagrangian the unitarity of the gauge boson scattering amplitudes is analyzed. The experimental fits and limits on the free parameters of the vector resonance triplet are investigated.