[en] Using relationships between open and closed strings, we present a construction of tree-level scattering amplitudes for gravitons minimally coupled to matter in terms of gauge theory partial amplitudes. In particular, we present examples of amplitudes with gravitons coupled to vectors or to a single fermion pair. We also present two examples with massive graviton exchange, as would arise in the presence of large compact dimensions. The gauge charges are represented by flavors of dynamical scalars or fermions. This also leads to an unconventional decomposition of color and kinematics in gauge theories. (c) 2000 The American Physical Society

[en] We consider the scattering amplitudes of the form V₁V₂→V₃V₄, where V_i=γ, Z, W or g (=gluon) are the standard model gauge bosons, due to graviton exchange in Kaluza-Klein theories with large extra dimensions. This leads to a number of experimentally viable signatures at high energy leptonic and hadronic colliders. We discuss the observability or attainable limits on the scale of the gravitational interactions (m_D), that may be obtained at an e⁺e^- Next Linear Collider (NLC) and at the CERN LHC, by studying some of these types of gauge-boson scattering processes. We find that the attainable limits through these type of processes are m_D(greater-or-similar sign)3 TeV at the NLC and m_D(greater-or-similar sign)6 TeV at the LHC. (c) 2000 The American Physical Society

[en] Gravity can become strong at the TeV scale in the theory of extra dimensions. An effective Lagrangian can be used to describe the gravitational interactions below a cutoff scale. In this work, we study the associated production of the gravitons with a Z boson or a photon at e⁺e^- colliders of energies of the CERN LEPII to the Next Linear Colliders (√(s)=0.25-1.5 TeV) and calculate the sensitivity to the new interactions. We also obtain the limit on the cutoff scale using the present data from LEPII. (c) 1999 The American Physical Society

[en] We propose a world-sheet realization of the zigzag-invariant strings as a perturbed WZNW model at large negative level. We argue that the gravitational dressing produces additional fixed points of the dressed renormalization beta function. One of these new critical points can be interpreted as a zigzag-invariant string model. (orig.)

[en] In a previous paper with G. Gibbons (1987) we derived a list of three dimensional symmetric space σ-models obtained by dimensional reduction of a class of four dimensional gravity theories with abelian gauge fields and scalars. Here we give a detailed analysis of their group theoretical structure leading to an abstract parametrization in terms of ''triangular'' group elements. This allows for a uniform treatment of all these models. As an interesting application we give a simple derivation of a ''quadratic mass formula'' for strictly stationary black holes. (orig.)

[en] We discuss the field theory limit of Dp-branes. In this limit, the black Dp-brane solution approaches a solution which is conformal to adS_p+2 x S^8-p. We argue that the frame in which the conformal factor is equal to one, the dual frame, is a 'holographic' frame. The radial coordinate of adS_p+2 provides a UV/IR connection as in the case of the D3 brane. The gravitational description involves gauged supergravities, typically with non-compact gauged groups. The near-horizon Dp-brane solution becomes a domain-wall solution of the latter. (orig.)

[en] The reaction e⁺p → e⁺X is studied with the H1 detector at Hera. The data cover momentum transfers Q² between 200 GeV² and 30000 GeV² and correspond to an integrated luminosity of 35.6 pb^-1. The differential cross section dσ/dQ² is compared to the standard model expectation for neutral current scattering and analysed to search for (ee)(qq) contact interactions. No evidence for new phenomena is observed. The results are used to set limits on scales within models of electron-quark compositeness, quark form factors and the exchange of virtual heavy leptoquarks. A search for gravitational effects mediated through the exchange of virtual gravitons which propagate into large extra dimensions is presented. (orig.)

[en] The status of two on-going studies concerning important aspects of the phenomenology of gauge-mediated supersymmetry breaking (GMSB) models at TeV colliders is reported. The first study deals with the characteristics of the light Higgs boson spectrum allowed by the (minimal and non-minimal) GMSB framework. Today's most accurate GMSB model generation and two-loop Feynman-diagrammatic calculation of m_h have been combined. The Higgs masses are shown in dependence of various model parameters at the messenger and electroweak scales. In the minimal model, an upper limit on m_h of about 124 GeV is found for m_t=175 GeV. The second study is focused on the measurement of the fundamental SUSY breaking scale √(F) at the LHC in the GMSB scenario where a stau is the next-to-lightest SUSY particle (NLSP) and decays into a gravitino with cτ_NLSP in the range 0.5 m to 1 km. This implies the measurement of mass and lifetime of long lived sleptons. The identification is performed by determining the time of flight in the ATLAS muon chambers. Accessible range and precision on √(F) achievable with a counting method are assessed. (orig.)

[en] The author describes spectral triples as generalized Dirac operators, the electroweak inner spectral triple, the application of the quantum Yang-Mills algorithm to the electroweak standard model sector, real spectral triples, the asymptotic heat-kernel expansion of the spectral action, tree approximation, the fermionic action, and the regular representation of the finite U_q(sl2)

[en] Cross-sections and angular distributions for hadronic and lepton pair final states in e⁺e^- collisions at a centre-of-mass energy near 189 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the standard model. The results are used to measure the energy dependence of the electromagnetic coupling constant α_em, and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a sneutrino in supersymmetric theories with R-parity violation. A search for the indirect effects of the gravitational interaction in extra dimensions on the μ⁺μ^- and τ⁺τ^- final states is also presented. (orig.)