Search

A Monte Carlo event generator is implemented for a two-Higgs-doublet model with maximal CP symmetry, the MCPM. The model contains five physical Higgs bosons; the ρ′, behaving similarly to the standard-model Higgs boson, two extra neutral bosons h′ and h″, and a charged pair H. The special feature of the MCPM is that, concerning the Yukawa couplings, the bosons h′, h″ and H couple directly only to the second-generation fermions but with strengths given by the third-generation-fermion masses. Our event generator allows the simulation of the Drell-Yan-type production processes of h′, h″ and H in proton-proton collisions at LHC energies. Also the subsequent leptonic decays of these bosons into the μ μ, μ ν and $\mu^{-} \bar{\nu}_{\mu}$ channels are studied as well as the dominant background processes. We estimate the integrated luminosities needed in pp collisions at center-of-mass energies of 8 and 14 TeV for significant observations of the Higgs bosons h′, h″ and H in these muonic channels. [ABSTRACT FROM AUTHOR]

We discuss the CP properties of the potential in the general two-Higgs-doublet model (THDM). This is done in a concise way using real gauge invariant functions built from the scalar products of the doublet fields. The space of these invariant functions, parametrising the gauge orbits of the Higgs fields, is isomorphic to the forward light cone and its interior. CP transformations are shown to correspond to reflections in the space of the gauge invariant functions. We consider CP transformations where no mixing of the Higgs doublets is taken into account as well as the general case where the Higgs basis is not fixed. We present basis independent conditions for explicit CP violation which may be checked easily for any THDM potential. Conditions for spontaneous CP violation, that is CP violation through the vacuum expectation values of the Higgs fields, are also derived in a basis independent way. [ABSTRACT FROM AUTHOR]

We study a two-Higgs doublet model with four generalised CP symmetries in the scalar sector. Electroweak symmetry breaking leads automatically to spontaneous breaking of two of them. We require that these four CP symmetries can be extended from the scalar sector to the full Lagrangian and call this requirement the principle of maximal CP invariance. The Yukawa interactions of the fermions are severely restricted by this requirement. In particular, a single fermion family cannot be coupled to the Higgs fields. For two fermion families, however, this is possible. Enforcing the absence of flavour-changing neutral currents, we find degenerate masses in both families or one family massless and one massive. In the latter case the Lagrangian is highly symmetric, with the mass hierarchy being generated by electroweak symmetry breaking. Adding a third family uncoupled to the Higgs fields and thus keeping it massless we get a model which gives a rough approximation of some features of the fermions observed in Nature. We discuss a number of predictions of the model which may be checked in future experiments at the LHC. [ABSTRACT FROM AUTHOR]

Determining the global minimum of Higgs potentials with several Higgs fields like the next-to-minimal supersymmetric extension of the standard model (NMSSM) is a non-trivial task already at the tree level. The global minimum of a Higgs potential can be found from the set of all its stationary points defined by a multivariate polynomial system of equations. We introduce here the algebraic Groebner basis approach to solve this system of equations. We apply the method to the NMSSM with CP-conserving as well as CP-violating parameters. The results reveal an interesting stationary-point structure of the potential. Requiring the global minimum to give the electroweak symmetry breaking observed in Nature excludes large parts of the parameter space. [ABSTRACT FROM AUTHOR]

We show that diffractive production of a single neutral pion in photon-induced reactions at high energy is dynamically suppressed due to the approximate chiral symmetry of QCD. These reactions have been proposed as a test of the odderon-exchange mechanism. We show that the odderon contribution to the amplitude for such reactions vanishes exactly in the chiral limit. This result is obtained in a nonperturbative framework and by using PCAC relations between the amplitudes for neutral pion and axial vector current production. [ABSTRACT FROM AUTHOR]

A method is presented for the analysis of the scalar potential in the general two-Higgs-doublet model. This allows us to give the conditions for the stability of the potential and for electroweak symmetry breaking in this model in a very concise way. These results are then applied to two different Higgs potentials in the literature, namely the MSSM and the two-Higgs-doublet potential proposed by Gunion et al. The known results for these models follow easily as special cases from the general results. In particular, for the potential of Gunion et al. we can clarify the stability and symmetry-breaking properties of the model with our method. [ABSTRACT FROM AUTHOR]

We present a study of anomalous electroweak gauge-boson couplings that can be measured in e+e- and γγ collisions at a future linear collider like ILC. We consider the gauge-boson sector of a locally SU(2)×U(1) invariant effective Lagrangian with ten dimension-six operators added to the Lagrangian of the standard model. These operators induce anomalous three-gauge-boson and four-gauge-boson couplings and an anomalous γγH coupling. We calculate the reachable sensitivity for the measurement of the anomalous couplings in γγ→WW. We compare these results with the reachable precision in the reaction e+e-→WW on the one hand and with the bounds that one can obtain from high-precision observables in Z decays on the other hand. We show that one needs both the e+e- and the γγ modes at an ILC to constrain the largest possible number of anomalous couplings and that the Giga-Z mode offers the best sensitivity for certain anomalous couplings. [ABSTRACT FROM AUTHOR]

We consider the gauge-boson sector of a locally SU(2) × U(1) invariant effective Lagrangian with ten dimension-six operators added to the Lagrangian of the standard model. These operators induce anomalous three- and four-gauge-boson couplings and an anomalous γγ H coupling. In the framework of this effective Lagrangian we calculate the helicity amplitudes and differential and total cross sections for the process γγ → WW at a photon collider. We give relations between different parts of the amplitudes that show which linear combinations of anomalous couplings are measurable in this reaction. The transformation properties of the differential cross section under CP are discussed. We find that three linear combinations of CP-conserving and of CP-violating couplings can be measured independently of the photon polarization in γγ → WW. [ABSTRACT FROM AUTHOR]

In contrast to theoretical expectations, experimental results at $\sqrt{s} = 200$ GeV for the reaction γ p → π0 X show no evidence for odderon exchange. The upper limit on the cross section is an order of magnitude smaller than the theoretical estimate. It is argued that chiral symmetry leads to a large suppression, taking the theoretical estimates well below the data. Two additional arguments are presented which may decrease the theoretical estimate further. The calculations are more sensitive to the assumptions made in evaluating the hadronic scattering amplitude than in the processes considered previously and lattice gauge calculations indicate that the odderon intercept may be appreciably lower than usually assumed. These two latter effects are particularly relevant for the reactions γ p → $f_2^0(1270) X$ and γ p → $a_2^0(1320) X$ for which the data upper limits are also below the theoretical predictions, but not so dramatically as for γ p → π0 X. [ABSTRACT FROM AUTHOR]

We study anomalous gauge-boson couplings induced by a locally SU(2) × U(1) invariant effective Lagrangian containing ten operators of dimension six built from boson fields of the standard model (SM) before spontaneous symmetry breaking (SSB). After SSB some operators lead to new three- and four-gauge-boson interactions, some contribute to the diagonal and off-diagonal kinetic terms of the gauge bosons, to the kinetic term of the Higgs boson and to the mass terms of the W and Z bosons. This requires a renormalisation of the gauge-boson fields, which, in turn, modifies the charged- and neutral-current interactions, although none of the additional operators contain fermion fields. Also the Higgs field must be renormalised. Bounds on the anomalous couplings from electroweak precision measurements at LEP and SLC are correlated with the Higgs-boson mass m H. Rather moderate values of anomalous couplings allow m H up to 500 GeV. At a future linear collider the triple-gauge-boson couplings $\gamma WW$ and ZWW can be measured in the reaction $e^ + e^- \rightarrow WW$. We compare three approaches to anomalous gauge-boson couplings: the form-factor approach, the addition of anomalous-coupling terms to the SM Lagrangian after and, as outlined above, before SSB. The translation of the bounds on the couplings from one approach to another is not straightforward. We show that it can be done for the process $e^ + e^- \rightarrow WW$ by defining new effective $\gamma WW$ and ZWW couplings. [ABSTRACT FROM AUTHOR]

Optimal observables are known to lead to minimal statistical errors on parameters for a given normalised event distribution of a physics reaction. Thereby all statistical correlations are taken into account. Therefore, on the one hand they are a useful tool to extract values on a set of parameters from measured data. On the other hand one can calculate the minimal constraints on these parameters achievable by any data-analysis method for the specific reaction. In case the final states can be reconstructed without ambiguities optimal observables have a particularly simple form. We give explicit formulae for the optimal observables for generic reactions in case of ambiguities in the reconstruction of the final state and for general parameterisation of the final-state phase space. [ABSTRACT FROM AUTHOR]

We discuss the angular distribution of the lepton pair in the Drell-Yan process,. This process gives information on the spin-density matrixof the annihilating quark-antiquark pair in. There is strong experimental evidence that even for unpolarised initial hadronsis non-trivial, and therefore the quark-antiquark system is polarised. We discuss the possibilities of a general- which could be entangled - and a factorising. We argue that instantons may lead to a non-trivialof the type indicated by experiments. [ABSTRACT FROM AUTHOR]

We analyze the pion electromagnetic, charged-current, and πγ transition form factors at time like momentum transfers q,q2 = s≤ 1.4 GeV2 using a dispersion approach. We discuss in detail the propagator matrix of the photon-vector meson system and define certain reduced amplitudes, or vertex functions, describing the coupling of this system to final states. We then apply the derived analytic expressions to the analysis of the recent e+e- →π+π-,τ-→π-πoVτ , and e+e-→π0γ data. We find the reduced amplitudes for the coupling of the photon and vector mesons to two pseudoscalars to be constant, independent of s, in the range considered, indicating a "freezing" of the amplitudes for s ≤1 GeV. The fit to the form factor data leads to the following values of the Breit-Wigner resonance masses mp- = 775.3 ± 0.8 MeV, mpo = 773.8 ± 0.6MeV and mω = 782.43 ± 0.05 MeV, where the errors are only statistical. [ABSTRACT FROM AUTHOR]

We review CP-violating effect in Z → 3 jet and Z → 4 jet decays, assuming the presence of CP-violating effective Zb&macrb;G and Zb&macrb;GG couplings. Longitudinal beam polarization is included in the studies. We response a direct search for such CP-violating couplings by using various CP-odd observables. The data of a future linear collider running at the Z-resonance in the so-called GigaZ option should give significant information on the couplings. Finally we show that stringent bonds on the mass of excited b quarks can be derived if appropriate couplings are of a size characteristic of a strong interaction. [ABSTRACT FROM AUTHOR]

The prospects of measuring triple gauge couplings in W pair production at future linear colliders with transverse beam polarisation are studied. We consider CP conserving and CP violating couplings with both real and imaginary parts. The maximum achievable sensitivity in a simultaneous measurement of all couplings is determined using optimal observables, extending an earlier analysis for longitudinal beam polarisation. We find good sensitivity to the coupling Im(R1 +?R), which is not measurable with longitudinal polarisation. In contrast, for the real parts (including the CP violating couplings) the sensitivity is better if both beams are longitudinally polarised. We conclude that a comprehensive measu-rement of all triple gauge couplings requires both transverse and longitudinal beam polarisation. [ABSTRACT FROM AUTHOR]

The prospects of measuring triple gauge couplings in W pair production at future linear colliders with transverse beam polarisation are studied. We consider CP conserving and CP violating couplings with both real and imaginary parts. The maximum achievable sensitivity in a simultaneous measurement of all couplings is determined using optimal observables, extending an earlier analysis for longitudinal beam polarisation. We find good sensitivity to the coupling Im(R1 +?R), which is not measurable with longitudinal polarisation. In contrast, for the real parts (including the CP violating couplings) the sensitivity is better if both beams are longitudinally polarised. We conclude that a comprehensive measu-rement of all triple gauge couplings requires both transverse and longitudinal beam polarisation. [ABSTRACT FROM AUTHOR]

The sensitivity of optimal integrated observables to electroweak triple gauge couplings is investigated for the process e-e+ → W-W+ → 4 fermions at future linear colliders. By a suitable reparameterisation of the couplings we achieve that all 28 coupling parameters have uncorrelated statistical errors and are naturally normalised for this process. Discrete symmetry properties simplify the analysis and allow checks on the stability of numerical results. We investigate the sensitivity to the couplings of the normalised event distribution and the additional constraints that can be obtained from the total rate. Particular emphasis is put on the gain in sensitivity one can achieve with longitudinal beam polarisation. We also point out questions that may best be settled with transversely polarised beams. In particular we find that with purely longitudinal polarisation one linear combination of coupling parameters is hardly measurable by means of the normalised event distribution. [ABSTRACT FROM AUTHOR]

We relate the structure functions of deep inelastic lepton-nucleon scattering to current-current correlation functions in a Euclidean field theory depending on a parameter r. The r-dependent Flamiltonian of the theory is P0 - (1 - r)P³, with P0 the usual Hamiltonian and P3 the third component of the momentum operator. We show that a small xBj in the structure functions corresponds to the small r limit of the effective theory. We argue that for r → 0 there is a critical regime of the theory where simple scaling relations should hold. We show that in this framework Regge behaviour of the structure functions obtained with the hard pomeron ansatz corresponds to a scaling behaviour of the matrix elements in the effective theory where the intercept of the hard pomeron appears as a critical index. Explicit expressions for various analytic continuations of the structure functions and matrix elements are given as well as path integral representations for the matrix elements in the effective theory. Our aim is to provide a framework for truly non-perturbative calculations of the structure functions at small XBj for arbitrary Q². [ABSTRACT FROM AUTHOR]

We examine diffractive proton-proton scattering $p \: p \to p \: X$ and photo- and electroproduction of $\rho^0$ mesons $\gamma^{(*)} \: p \to \rho^0 \: X$, where X denotes a proton or a final state, into which the proton can go by diffractive dissociation. Using a functional integral approach we derive the scattering amplitudes, which are governed by the expectation values of light-like Wegner-Wilson loops, which are then evaluated using the model of the stochastic vacuum. For the proton, we assume a quark-diquark structure. From the scattering amplitudes we calculate total and differential cross sections for high centre of mass energy and small momentum transfer and compare with experiments. Furthermore we calculate isovector form factors for the proton and the pion within the same model. [ABSTRACT FROM AUTHOR]

The single-particle inclusive differential cross-section for a reaction $a+b\to c+X$ is written as the imaginary part of a correlation function in a forward scattering amplitude for $a+b\to a+b$ in a modified effective theory. In this modified theory the interaction Hamiltonian $\tilde H_I$ equals $H_I$ in the original theory up to a certain time. Then there is a sign change and $\tilde H_I$ becomes nonlocal. This is worked out in detail for scalar field models and for QED plus the abelian gluon model. A suitable path integral for direct calculations of inclusive cross sections is presented. [ABSTRACT FROM AUTHOR]

We calculate high-energy photoproduction of the tensor meson $f_2(1270)$ by odderon and photon exchange in the reaction $\gamma +{\rm{p}} \rightarrow f_2(1270) +{\rm{X}}$, where X is either the nucleon or the sum of the N(1520) and N(1535) baryon resonances. Odderon exchange dominates except at very small transverse momentum, and we find a cross section of about 20 nb at a centre-of-mass energy of 20 GeV. This result is compared with what is currently known experimentally about $f_2$ photoproduction. We conclude that odderon exchange is not ruled out by present data. On the contrary, an odderon-induced cross section of the above magnitude may help to explain a puzzling result observed by the E687 experiment. [ABSTRACT FROM AUTHOR]

We analyse CP-violating effects in Z $\rightarrow$ 4 jet decays, assuming the presence of a CP-violating effective triple gluon coupling. We discuss the influence of this coupling on the decay width. Furthermore, we analyse different CP-odd observables and propose strategies of a direct search for such a CP-violating GGG coupling. The present data of LEP 1 should give significant information on the coupling. [ABSTRACT FROM AUTHOR]

We analyse CP-violating effects in Z $\rightarrow$ 4 jet decays, assuming the presence of CP-violating effective $Z b \bar{b} G$$ and $Z b \bar{b} G G$ couplings. We discuss the influence of these couplings on the decay width. Furthermore, we propose various strategies of a direct search for such CP-violating couplings by using different CP-odd observables. The present data of LEP 1 should give significant information on the couplings. [ABSTRACT FROM AUTHOR]

We consider a spontaneously broken gauge theory based on the standard model (SM) group $G = SU(2)\times U(1)$ with scalar fields that carry arbitrary representations of G, and we investigate some general properties of the charged and neutral current involving these fields. In particular we derive the conditions for having real or complex couplings of the Z boson to two different neutral or charged scalar fields, and for the existence of CP-violating Z-scalar-scalar couplings. Moreover, we study models with the same fermion content as in the SM, with one SU(2) Higgs singlet, and an arbitrary number of Higgs doublets. We show that the structure of the Z-Higgs boson and of the Yukawa couplings in these models can be such that CP-violating $Zb{\bar b}G$ form factors which conserve chirality are induced at the one-loop level. [ABSTRACT FROM AUTHOR]

We investigate the reaction ${\rm e}\;{\rm p} \rightarrow{\rm e}\;{\rm PS}\;{\rm X}$ where PS denotes a pseudoscalar meson $\pi^0$, $\eta$, $\eta'$, or $\eta_c$ and X either a proton or resonance or continuum state into which the proton can go by diffractive excitation. At high energies photon and odderon exchange contribute to the reaction. The photon exchange contribution is evaluated exactly using data for the total virtual photon-proton absorption cross section. The odderon exchange contribution is calculated in nonperturbative QCD, using functional integral techniques and the model of the stochastic vacuum. For the proton we assume a quark-diquark structure as suggested by the small odderon amplitude in pp and $ {\rm p} \bar{{\rm p}}$ forward scattering. We show that odderon exchange leads to a much larger inelastic than elastic PS production cross section. Observation of our reaction at HERA would establish the soft odderon as an exchange object on an equal footing with the soft pomeron and would give us valuable insight into both the nucleon structure and the mechanism of high energy diffractive scattering. [ABSTRACT FROM AUTHOR]

Total and differential cross sections for high energy and small momentum transfer elastic hadron-hadron scattering are studied in QCD using a functional integral approach. The hadronic amplitudes are governed by vacuum expectation values of lightlike Wegner-Wilson loops, for which a matrix cumulant expansion is derived. The cumulants are evaluated within the framework of the Minkowskian version of the model of the stochastic vacuum. Using the second cumulant, we calculate elastic differential cross sections for hadron-hadron scattering. The agreement with experimental data is good. [ABSTRACT FROM AUTHOR]

Exclusive pseudoscalar meson production in $ep$ scattering at high energies is a direct probe for a possible “odderon” exchange in soft hadronic processes. Using a simple phenomenological ansatz for the odderon, we demonstrate how it can be separated from the contribution due to photon-photon fusion, and the relevant parameters be measured. Total cross sections and differential distributions are presented for $\pi^0,\eta,\eta'$, and $\eta_c$ production. Results are given from both a full calculation and one using the equivalent photon approximation. The accuracy of the latter is discussed. [ABSTRACT FROM AUTHOR]

We propose to test the CP symmetry in the reactions Z → μ+μ−γ and Z → τ+τ−γ. The experimental analysis of angular correlations allows to determine a set of effective couplings: the electric and weak dipole moments of the muon and the tau lepton, and in particular chirality conserving 4-particle couplings, all of which can be induced by CP-violation in renormalizable theories of electroweak interactions beyond the Standard Model. We update an indirect bound on the weak dipole moment of the muon. [ABSTRACT FROM AUTHOR]

We discuss how to measure anomalous WWZ- and WWγ-couplings with minimal statistical error using integrated observables, without having to assume that the anomalous couplings are small. We propose a parametrisation of these couplings which is well suited for the extraction of both single and many parameters, and which leads to a very simple form of the integrated cross section, from which additional information on the couplings can be obtained. [ABSTRACT FROM AUTHOR]