Universal and Non Universal New Physics Effects in a General Four-fermion Process: a Z-peak Subtracted Approach

We calculate, using a Z-peak subtracted representation of four-fermion processes previously illustrated for the case of electron-positron annihilation into charged lepton-antilepton, the corresponding expressions of the new physics contributions for the case of final quark-antiquark states, allowing the possibility of both universal and non universal effects. We show that, in each case, the main result obtained for the final lepton channel can be generalized, so that every experimentally measurable quantity can be expressed in terms of input parameters \underline{measured} on Z resonance, of $\alpha(0)$ and of a small number of subtracted one loop expressions. Some examples of models are considered for several c.m. energy values, showing that remarkable simplifications are often introduced by our approach. In particular, for the case of a dimension-six lagrangian with anomalous gauge couplings, the same reduced number of parameters that would affect the observables of final leptonic states are essentially retained when one moves to final hadronic states. This leads to great simplifications in the elaboration of constraints and, as a gratifying byproduct, to the possibility of making the signal from these models clearly distinguishable from those from other (both universal and non universal) competitors.Comment: 21 pages + 3 figures in ps file, corrected version. (e-mail [email protected]

Signals for Neutralino Box Effects at LEP2

We have computed the contribution to the observables of the final two fermion channel at LEP2, at the limiting energy $\sqrt{q^2}=200 GeV$, coming from boxes with two neutralinos of purely gaugino type, of mass $M=100 GeV$. We find a potentially visible effect only for the muon channel, in the cross section and, to a lesser extent, in the forward-backward asymmetry. Analogous effects coming from the chargino box are also briefly discussed.Comment: 10 pages and 2 figures. e-mail: [email protected]

Constraints on anomalous gauge couplings from present LEP1 and future LEP2, BNL data

We analyze, in a rather general model where anomalous triple gauge couplings are present, the visible effects in R$_b$ (measured at LEP1), in W pair production (to be measured at LEP2) and in the muon anomalous magnetic moment (to be measured at BNL). From the combination of the three experiments a remarkable improvement on the pure LEP2 constraints is obtained.Comment: 10 pages and 6 figures. e-mail: [email protected]

Logarithmic Fingerprints of Virtual Supersymmetry

We consider the high energy behaviour of the amplitudes for production of leptons, quarks, Higgs bosons, sleptons, squarks, gauge bosons, charginos, neutralinos. We concentrate our discussion on the universal (process independent) logarithmic terms which factorize the Born amplitude and which are typically of the form [a ln(s/m^2)-ln^2(s/m^2)]. We perform a systematic determination of the coefficient "a" for the various final states and we emphasize the striking features which differentiate the SM and the MSSM cases. We show that a comparison with experiments at future colliders should provide a clean way to test the gauge and Higgs structures of the electroweak interactions owing to the presence of sizeable (visible) virtual logarithmic supersymmetric contributions.Comment: 11 pages e-mail: [email protected]

Designing III-V Multijunction Solar Cells on Silicon

Single junction Si solar cells dominate photovoltaics but are close to their efficiency limits. This paper presents ideal limiting efficiencies for tandem and triple junction multijunction solar cells subject only to the constraint of the Si bandgap and therefore recommending optimum cell structures departing from the single junction ideal. The use of III-V materials is considered, using a novel growth method capable of yielding low defect density III-V layers on Si. In order to evaluate the real potential of these proposed multijunction designs, a quantitative model is presented, the strength of which is the joint modelling of external quantum efficiency and current-voltage characteristics using the same parameters. The method yields a single parameter fit in terms of the Shockley-Read-Hall lifetime. This model is validated by fitting experimental data of external quantum efficiency, dark current, and conversion efficiency of world record tandem and triple junction cells under terrestrial solar spectra without concentration. We apply this quantitative model to the design of tandem and triple junction solar cells, yielding cell designs capable of reaching efficiencies without concentration of 32% for the best tandem cell and 36% for the best triple junction cell. This demonstrates that efficiencies within a few percent of world records are realistically achievable without the use of concentrating optics, with growth methods being developed for multijunction cells combining III-V and Si materials.Comment: Preprint of the paper submitted to the journal Progress in Photovoltaics, selected by the Executive Committee of the 28th EU PVSEC 2013 for submission to Progress in Photovoltaics. 10 pages, 7 figure

Complete electroweak one loop contributions to the pair production cross section of MSSM charged and neutral Higgs bosons in e+e- collisions

In this paper, we review the production cross section for charged and neutral Higgs bosons pairs in $e^{+}e^{-}$ collisions beyond the tree level, in the framework of the Minimal Supersymmetric Standard Model (MSSM). A complete list of formulas for all electroweak contributions at the one loop level is given. A numerical code has been developed in order to compute them accurately and, in turn, to compare the MSSM Higgs bosons pair production cross sections at tree level and at the one loop level.Comment: 58 pages, 3 eps figure