Higgs production in association with top quark pair at e+e- colliders in theories of higher dimensional gravity

The models of large extra compact dimensions, as suggested by Arkani-Hamed, Dimopoulos and Dvali, predict exciting phenomenological consequences with gravitational interactions becoming strong at the TeV scale. Such theories can be tested at the existing and future colliders. In this paper, we study the contribution of virtual Kaluza-Klein excitations in the process $e^+e^- \to t \bar t H$ at future linear collider (NLC). We find that the virtual exchange KK gravitons can modify the cross-section $\sigma(e^+e^- \to t \bar t H)$ significantly from its Standard Model value and will allow the effective string scale to be probed up to 7.9 TeV.Comment: 10 pages, Latex, 4 postscript figure

Constraining Supersymmetry

We review constraints on the minimal supersymmetric extension of the Standard Model (MSSM) coming from direct searches at accelerators such as LEP, indirect measurements such as b -> s gamma decay and the anomalous magnetic moment of the muon. The recently corrected sign of pole light-by-light scattering contributions to the latter is taken into account. We combine these constraints with those due to the cosmological density of stable supersymmetric relic particles. The possible indications on the supersymmetric mass scale provided by fine-tuning arguments are reviewed critically. We discuss briefly the prospects for future accelerator searches for supersymmetry.Comment: 21 LaTeX pages, 9 eps figures, Invited Contribution to the New Journal of Physics Focus Issue on Supersymmetr

Forward tracking at the next e+ e- collider part I: the physics case

In a series of notes we explore the detector requirements of the forward tracking region for a future $e^+ e^-$ collider with a center-of-mass energy in the range from 500 GeV to 3 TeV. In this first part we investigate the relevance of the forward region for a range of physics processes that are likely to be relevant in such a machine. We find that many examples can be found where excellent performance of the forward detector system may lead to a considerable increase of the physics output of the experiment. A particularly clear physics case can be made for the reconstruction of electrons at small polar angle.Comment: category: instrumentation

Probing the Z? sector of the minimal B?L model at future linear colliders in the e+e? ? ?+?? process

We study the capabilities of future electron-positron Linear Colliders, with centre-of-mass energy at the TeV scale, in accessing the parameter space of a Z' boson within the minimal B?L model. In such a model, wherein the Standard Model gauge group is augmented by a broken U(1)B?L symmetry – with B(L) being the baryon(lepton) number — the emerging Z' mass is expected to be in the above energy range. We carry out a detailed comparison between the discovery regions mapped over a two-dimensional configuration space (Z' mass and coupling) at the Large Hadron Collider and possible future Linear Colliders for the case of di-muon production. As known in the literature for other Z' models, we confirm that leptonic machines, as compared to the CERN hadronic accelerator, display an additional potential in discovering a B?L Z' boson as well as in allowing one to study its properties at a level of precision well beyond that of any of the existing colliders