Tests of Higgs Boson Couplings at a mu+mu- Collider

We investigate the potential of a muon collider for testing the presence of anomalous Higgs boson couplings. We consider the case of a light (less than $160 GeV$) Higgs boson and study the effects on the Higgs branching ratios and total width, which could be induced by the non standard couplings created by a class of dim=6 $SU(3)\times SU(2)\times U(1)$ gauge invariant operators satisfying the constraints imposed by the present and future hadronic and $e^-e^+$ colliders. For each operator we give the minimal value of the $\mu^+\mu^-$ integrated luminosity needed for the muon collider ($\mu C$) to improve these constraints. Depending on the operator and the Higgs mass, this minimal $\mu C$ luminosity lies between $0.1 fb^{-1}$ and $100 fb^{-1}$.Comment: 18 pages and 4 figures; version to be published in Phys. Rev.D. e-mail: [email protected]

A Model-independent Description of New Physics effects in e+e- to t tbar

We study the potential of a future $e^+e^-$ collider for the search of anomalous gamma t t bar and Z t t bar couplings, assuming that CP-invariance holds. This is done in a model-independent way, considering that all six possible couplings do appear. Two experimental situations are envisaged, with and without electron beam polarization. Observability limits in the form of domains in the 6-dimensional parameter space are established. Illustrations for specific constrained models are also presented and implications for new physics searches are discussed.Comment: 26 pages and 5 figures. e-mail: [email protected]

Signatures of the anomalous ZγZ\gamma and ZZ production at the lepton and hadron Colliders

The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ \gamma$ and $Z\gamma \gamma$ vertices, is critically examined. Their signatures and the possibilities to study them, through ZZ and $Z\gamma$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. Experimental limits obtained or expected on each coupling are collected. A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure.Comment: 17 pages and 9 figures, version to appear in Phys. ReV. e-mail: [email protected]

A FORTRAN code for γγ→ZZ\gamma \gamma \to Z Z in SM and MSSM

Through the present paper, the code gamgamZZ is presented, which may be used to calculate all possible observables related to the process $\gamma \gamma \to ZZ$, in either the Standard Model (SM), or the minimal sypersymmetric standard model (MSSM) with real parameters.Comment: 13 pages, 7 figures Revised according to the EPJC Referee suggestion

Unitarity Constraints for New Physics Induced by dim-6 Operators

We compute the helicity amplitudes for boson-boson scattering at high energy due to the operators \O_{B\Phi}, \O_{W\Phi} and \O_{UB}, and we derive the corresponding unitarity bounds. Thus, we provide relations between the couplings of these operators and the corresponding New Physics thresholds, where either unitarity is saturated or new degrees of freedom are excited. We compare the results with those previously obtained for the operators \O_W and \O_{UW} and we discuss their implications for direct and indirect tests at present and future colliders. The present treatment completes the study of the unitarity constraints for all blind bosonic operators.Comment: 41 pages, latex file. PM 94-28 THES-TP 94-0

Unitarity Constraints for Transverse Gauge Bosons at LEP and Supercolliders

Using asymptotic helicity amplitudes for Vector-Vector, Vector-Higgs and Higgs-Higgs scattering, we establish the unitarity constraints on the $SU(2)_c$ conserving and $W_\mu$ depending interactions, which at sufficiently high energies may create strong forces among the transverse vector boson and Higgs states. We then derive upper bounds for the couplings of these interactions, which depend on the high energy scale where unitarity is saturated. If \eg\, unitarity is saturated at 1TeV, then \lambda_W \lsim 0.12 is obtained. The implied relations between the present and future LEP results, and the possible observations of strong effects at supercolliders, are also discussedComment: 11 pages,postscript file of 1 figure appended at the end of the latex file (e-mail [email protected] PM/93-37 THES-TP 93/1

Vector boson Pair Production at Supercolliders; useful approximate helicity amplitudes

We study vector boson pair production at $LHC$ and $SSC$, taking into account the effects generated by the anomalous vector boson and Higgs couplings induced by the operators ${\cal O}_W$ and ${\cal O}_{UW}$, which are the only dim=6 operators preserving $SU(2)_c$. These operators lead to enhanced production of transverse vector bosons, as opposed to the enhanced production of longitudinal gauge bosons, induced in case M_H\gsim 1\ TeV, by dim=4 terms already existing in the Standard Model lagrangian. For vector boson pair masses larger than $1\ TeV$, we establish very simple approximate expressions for the standard as well as the non-standard helicity amplitudes for $q\bar q$ annihilation and vector boson fusion, which accurately describe the physics. These expressions should simplify the experimental search for such interactions. We finally discuss the observability and the disentangling of these interactions.Comment: 22 pages, 6 figures avaible by air mail upon request , (e-mail [email protected] PM/93-26 THES-TP 93/

Light by Light Scattering at High Energy: a Tool to Reveal New Particles

We point out a few remarkable properties of the $\gamma\gamma\to\gamma\gamma$ process at high energy. They should allow to search for effects of new particles and interactions. We give illustrations with threshold effects due to pairs of new charged particles (charginos, charged Higgses, sfermions), resonance effects due to s-channel production of neutral scalars (standard or supersymmetric Higgs particles, technipions) and unitarity saturating amplitudes due to a strongly interacting sector. The use of polarized photon beams is also briefly discussed.Comment: 8 pages and 3 figures, typos corrected. e-mail: [email protected]

Tests of Anomalous Higgs Boson Couplings through e−e+→HZe^-e^+ \to HZ and HγH\gamma

We show how the processes $e^- e^+ \to ZH, ~ \gamma H$, which will be studied at LEP2 and at high energy colliders, could be used to search for types of New Physics (NP) characterized by an effective NP scale in the few TeV range and affecting the scalar sector only. In particular, for $e^- e^+ \to Z H$, we propose the measurement of suitable azimuthal asymmetries determined from the angular distribution of the $Z$-decay plane with respect to the $Z$-production one. Such asymmetries, together with the $ZH$ angular distribution, may allow a complete disentangling of the five $dim=6$ operators ${\cal O }_{UB}$, ${\cal O }_{UW}$, $\overline{{\cal O }}_{UB}$, $\overline{{\cal O }}_{UW}$, ${\cal O }_{\Phi2}$, describing the residual NP effects to the Higgs couplings. We note that the first four of these operators contribute to processes relevant to LEP1 precision measurements only at the 1-loop level, while the last operator remains completely unconstrained at this level. The process $e^- e^+ \to \gamma H$ is also very sensitive to NP and should bring important independent information.Comment: 20 pages + 9 figures in .uu files. revised version (corrected scales). (e-mail [email protected]

The Equivalence Theorem and Effective Lagrangians

We point out that the equivalence theorem, which relates the amplitude for a process with external longitudinally polarized vector bosons to the amplitude in which the longitudinal vector bosons are replaced by the corresponding pseudo-Goldstone bosons, is not valid for effective Lagrangians. However, a more general formulation of this theorem also holds for effective interactions. The generalized theorem can be utilized to determine the high-energy behaviour of scattering processes just by power counting and to simplify the calculation of the corresponding amplitudes. We apply this method to the phenomenologically most interesting terms describing effective interactions of the electroweak vector and Higgs bosons in order to examine their effects on vector-boson scattering and on vector-boson-pair production in $f\bar{f}$ annihilation. The use of the equivalence theorem in the literature is examined.Comment: 20 pages LaTeX, BI-TP 94/1