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Register a new userSUSY QCD corrections to the polarization and spin correlations of top quarks produced in e+e- collisions
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We compute the supersymmetric QCD corrections to the polarization and the spin correlations of top quarks produced above threshold in e+e- collisions, taking into account arbitrary longitudinal polarization of the initial beams.
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We calculate one-loop radiative QCD corrections to the three polarized and unpolarized structure functions that determine the beam-quark polar angle dependence of the alignment (or longitudinal) polarization of light and heavy quarks produced in e^+e^- annihilations. We present analytical and numerical results for the alignment polarization and its polar angle dependence. We discuss in some detail the zero-mass limit of our results and the role of the anomalous spin-flip contributions to the polarization observables in the zero-mass limit. Our discussion includes transverse and longitudinal beam polarization effects.
We study the pair production of scalar top quarks in e+e- collisions with the subsequent decay of the top squarks into b-quarks and charginos. We simulate this process using PYTHIA6.4 for beam energies 2E_beam = 350, 400, 500, 800, 1000 GeV. Proposing a set of criteria we obtain a good separation of the signal stop events from top quark pair production which is the main background. The number of stop production events obtained with the proposed cuts for different energies is calculated for an integrated luminosity of 1000 1/fb. We propose a method to reconstruct the mass of the top squark, provided the mass of the lightest neutralino is known, and estimate the error of the mass determination for the case sqrt{s} = 500 GeV.
We calculate the longitudinal contribution to the alignment polarization $Pl$ of quarks produced in $e^+e^-$ annihilation. In the Standard Model, the longitudinal alignment polarization vanishes at the Born term level and thus receives its first non-zero contribution from the $O(as)$ tree graph process. We provide analytical and numerical results for the longitudinal alignment polarization of massless and massive quarks, in particular for the recently discovered top quark.
The effect of virtual electroweak corrections to $e^+e^- rightarrow t bar{t}$ and the contribution of the radiation processes $e^+e^- rightarrow tbar{t}Z, tbar{t}H$ to the inclusive top pair production cross section and forward-backward asymmetry are discussed in the high energy regime.
The calculation of the cosmological relic density of the dark matter candidate within supersymmetric models is an interesting possibility to obtain additional constraints on the supersymmetric parameter space with respect to collider, electroweak precision, and low-energy data. Considering future cosmological precision measurements, radiative corrections can play an important role in the analysis. We present full QCD and SUSY-QCD corrections to neutralino pair annihilation into quark-antiquark pairs and analyze their impact on the neutralino annihilation cross section and the relic density. By comparing to the relic density obtained from a pure leading order calculation, we show that the corrections strongly influence the extraction of SUSY mass parameters from cosmological data.
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