Probing Contact Interactions at High Energy Lepton Colliders

Fermion compositeness and other new physics can be signalled by the presence of a strong four-fermion contact interaction. Here we present a study of $\ell\ell qq$ and $\ell\ell\ell'\ell'$ contact interactions using the reactions: $\ell^+ \ell^- \to \ell'^+\ell'^-,b\bar b, c\bar c$ at future $e^+e^-$ linear colliders with $\sqrt s=0.5-5$ TeV and $\mu^+\mu^-$ colliders with $\sqrt s=0.5,4$ TeV. We find that very large compositeness scales can be probed at these machines and that the use of polarized beams can unravel their underlying helicity structure.Comment: 12 pg, to appear in the {\it Proceedings of the 1996 DPF/DPB Summer Study on New Directions for High Energy Physics - Snowmass96}, Snowmass, CO, 25 June - 12 July, 199

Collider phenomenology of Higgs bosons in Left-Right symmetric Randall-Sundrum models

We investigate the collider phenomenology of a left-right symmetric Randall-Sundrum model with fermions and gauge bosons in the bulk. We find that the model is allowed by precision electroweak data as long as the ratio of the (unwarped) Higgs vev to the curvature scale is $v/k \le 1/4$. In that region there can be substantial modifications to the Higgs properties. In particular, the couplings to $WW$ and $ZZ$ are reduced, the coupling to gluons is enhanced, and the coupling to $\gamma\gamma$ can receive shifts in either direction. The Higgs mass bound from LEP II data can potentially be relaxed to $m_H \gtrsim 80$ GeV.Comment: 21 pages, 11 figures. Minor changes to numerics; replaced with published versio

Comment on Z′Z''s and the H1 and ZEUS High Q2Q^2 Anomalies

We investigate the effects of extra neutral gauge bosons on the high $Q^2$ region of the $e^+p \to e^+ X$ cross section at $\sqrt{s}=300$ GeV. We found that the only models with electroweak strength coupling, typical of extended gauge theories, that give a better fit to the H1 and ZEUS high $Q^2$ data than the standard model, are ruled out by existing data from the Tevatron. From general scaling arguments, using the allowed contact interactions, the only allowed models with $Z'$'s would be those with strong couplings although even in this case the statistical evidence is not compelling.Comment: Latex file uses revtex version 3, epsfig, 1 postscript figure is attache

Bounds on R-parity Violation from Resonant Slepton Production at the LHC

We consider the ATLAS and CMS searches for dijet resonances, as well as the ATLAS search for like-sign dimuon pairs at the LHC with 7 TeV center of mass energy. We interpret their exclusions in terms of bounds on the supersymmetric R-parity violating parameter space. For this we focus on resonant slepton production followed by the corresponding decay.Comment: 17 pages, 11 figures, 3 table

Probing Large Extra Dimensions Using Top Production in Photon-Photon Collisions

Theories with large extra dimensions predict an infinite tower of Kaluza-Klein states in the 1 TeV range, which can consequently have significant implications for experimental observables. One such observable, which gets affected by the exchange of spin-2 Kaluza-Klein particles, is the t t(bar) production cross-section in photon-photon collisions at NLC energies. We study this process and obtain bounds on the effective quantum gravity scale M_S between 700 and 2400 GeV (depending on the centre-of-mass energy). We show that the use of polarisation will further strengthen these bounds.Comment: 9 pages, latex, 2 ps figures, numerical errors corrected which has improved the final result

Bounds on the Masses and Couplings of Leptoquarks from Leptonic Partial Widths of the Z

The vertex corrections to the leptonic partial widths of the $Z$ induced by leptoquarks that couple leptons to the top quark are considered. We obtain stringent bounds on the parameter space of the masses and Yukawa couplings of these leptoquarks, using the latest information on the $Z \rightarrow l^+l^-$ decay widths measured at LEP. Leptoquarks coupling with electroweak strength to top quarks are constrained to be heavier than several hundred GeV, at 95$\%$ C.L. As a consequence, such leptoquarks cannot make a significant contribution to lepton asymmetries, $\tau$ polarisation asymmetries or $A_{LR}$.Comment: 11 pages + 3 Figures (available upon request), Latex file, CERN preprint CERN-TH.7280/9

Unique Identification of Graviton Exchange Effects in e^+ e^- Collisions

Many types of new physics can lead to contact interaction-like modifications in e^+ e^- processes below direct production threshold. We examine the possibility of uniquely identifying the effects of graviton exchange, which are anticipated in many extra dimensional theories, from amongst this large set of models by using the moments of the angular distribution of the final state particles. In the case of the e^+ e^- --> f bar{f} process we demonstrate that this technique allows for the unique identification of the graviton exchange signature at the 5 sigma level for mass scales as high as 6 sqrt(s). The extension of this method to the e^+ e^- --> W^+ W^- process is also discussed.Comment: 21 pages, 3 figs, LaTe

Zeroing in on Supersymmetric Radiation Amplitude Zeros

Radiation amplitude zeros have long been used to test the Standard Model. Here, we consider the supersymmetric radiation amplitude zero in chargino-neutralino associated production, which can be observed at the luminosity upgraded LHC. Such an amplitude zero only occurs if the neutralino has a large wino fraction and hence this observable can be used to determine the neutralino eigenstate content. We find that this observable can be measured by comparing the p_T spectrum of the softest lepton in the trilepton $\chi_1^\pm \chi_2^0$ decay channel to that of a control process such as $\chi_1^+ \chi_1^-$ or $\chi_2^0 \chi_2^0$. We test this technique on a previously generated model sample of the 19 dimensional parameter space of the phenomenological MSSM, and find that it is effective in determining the wino content of the neutralino.Comment: 19 pages, 7 figure