SUSY virtual effects at the LEP2 boundary

We examine the possibility that SUSY particles are light, i.e. have a mass just beyond the final kinematical reach of LEP2. In this case, even if light particles are not directly detected, their virtual effects are enhanced by a “close-to-threshold” resonance in the s-channel. We find that this resonant effect is absent in the case of light sfermions, while it is enhanced in the case of light gauginos, since neutralinos and charginos add coherently in some regions of the allowed parameter space. We discuss this “virtual alliance” in detail and try to examine the possibilities of its experimental verification. Received: 19 March 1999 / Published online: 12 August 1999     

Test of Higgs boson nature in e+e−→HHZ

The process e⁺e^?→HHZ is strongly dependent on the Higgs boson couplings HZZ, HHZZ and HHH, and provides therefore a test of the Higgs assignment to gauge group representations. The cross section varies between 5 × 10^?38 and 10^?39 cm² for Higgs masses between 5GeV and 40 GeV in the Weinberg-Salam model.     

Constraints on non-standard effects from present and futureg μ−2 measurements

Motivated by the expected high accuracy of the next AGS measurement of the muong?2 we have computed several types of contributions arising from new particles and interactions. Results are first given for individual terms where limits on new parameters, coming fromg _μ?2 are compared to those expected from future colliders. Combined effects due to different contributions are then considered and this reveals that constrained models with a low effective scale could still be allowed.     

Anomalous effects ine + e − annihilation into boson pairs I.e + e −→W + W −

We present a phenomenological analysis of the various kinds of anomalous effects which can apper either in the leptonic or in the bosonic sector of the reactionse ⁺ e ^?→V V′(V V′=W ^±,Z ⁰ or γ). A general descritpin of invariant amplitudes and helicity amplitudes is given. Applications are made with non standar couplings, new intermediate states, residuale ⁺ e ^? VV′ contact interactions. In this first part results are given fore ⁺ e ^?→W ⁺ W ^? in view of LEP 200 and future linear colliders in the TeV range.     

Charge density transport in a novel halogened transition metal tetrachalcogenide (NbSe4)3.33I

We report the observation of non linear electrical conductivity above a sharp threshold field and of a periodic signal in the a.c. voltage for a novel linear chain compound (NbSe₄)_3.33I below a phase transition which occurs at T_c = 285 K. We conclude that this halogened metal transition tetrachalcogenide is a new compound which exhibits Peierls-Fröhlich charge density wave transport.     

Anomalous couplings in single Higgs production throughγγ collisions

We show that single Higgs production inγγ collisions through laser backscattering provides the best way to look for New Physics (NP) effects inducing anomalous Higgs couplings. Our analysis is based on the fourdim=6 operators ${\mathcal{O}}_{UB} , {\mathcal{O}}_{UW, } \bar {\mathcal{O}}_{UB} $ , and $\bar {\mathcal{O}}_{UW} $ which describe New Physics effects in this sector. Using the Higgs production rate we establish observability limits for the couplings of the aforementioned operators at a level of 10^?3, which means establishing lower bounds on the scale of NP of the order 30 to 200 TeV. Higgs branching ratios, especially the ratio Γ(H→γγ)/Γ(H→γZ), are shown to provide powerful ways to disentangle the effects of the various operators.