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Register a new userSingle sneutrino production in $gammagamma$ collisions
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We study the single production of sneutrinos with two leptons (or jets) via $gammagamma$ collision in an R-parity ($R_{p}$) violating supersymmetric model. The subsequent decays of the sneutrino are also considered. The single production of sneutrinos may provide a significant test of supersymmetry and $R_p$-violation with flavour conserving and flavour changing final states. If such processes coming from $R_p$ violation are not detected, the parameter space of the model will be strongly constrained at the future Linear Collider.
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Understanding the data on the total cross section $sigma_{tot}($e$^+$e$^-to$e$^+$e$^-bbar{b})$ measured at LEP2 represents a serious challenge for perturbative QCD. In order to unravel the origins of the discrepancy between data and theory, we investigate the dependence of four contributions to this cross section on $gammagamma$ collision energy. As the reliability of the existing calculations of $sigma_{tot}($e$^+$e$^-to$e$^+$e$^-bbar{b})$ depends, among other things, on the stability of calculations of the cross section $sigma_{tot}(gammagammato bbar{b})$ with respect to variations of the renormalization and factorization scales, we investigate this aspect in detail. We show that in most of the region relevant for the LEP2 data the existing QCD calculations of $sigma_{tot}(gammagammato bbar{b})$ do not exhibit a region of local stability and should thus be taken with caution. The source of this instability is suggested and its phenomenological implications for LEP2 data are discussed.
We study the single production of scalar neutrinos or charginos via $gammagamma$ collision in an R-parity ($R_{p}$) violating supersymmetric model. It may be possible to detect a sneutrino or a chargino at a Linear Collider (LC) in $gamma gamma$ operation mode, as a test of supersymmetry and $R_p$-violation. Because of the clean background in LC, stringent constraints on $R_p$ violating parameters can be obtained even if the process cannot be observed at the future Linear Collider.
We examine for representative gaugino-higgsino mixing scenarios sneutrino-neutralino and sneutrino-chargino production in deep inelastic ep-scattering at the cm-energy of 1.8 TeV. The cross sections for sneutrino-chargino production are more than one order of magnitude bigger than those for sneutrino-squark production. Also for zino-like neutralinos we find cross sections at least comparable to those for sneutrino-squark production.
We have studied the associated production processes of a neutral top-Higgs in the topcolor assisted technicolor model with a pair of heavy quarks in gammagamma collisions at the International Linear Collider (ILC). We find that the cross section for tbar{t}h_t in gammagamma collisions is at the level of a few fb with the c.m. energy sqrt{s}=1000 GeV, which is consistent with the results of the cross section of tbar{t}H in the standard model and the cross section of tbar{t}h in the minimal supersymmetric standard modeland the little Higgs models. It should be distinct that hundreds of to thousands of h_t per year can be produced at the ILC, this process of gammagamma to tbar{t}h_t is really interesting in testing the standard model and searching the signs of technicolor.
In this article, we investigate the contribution of the higher twist Feynman diagrams to the large-$p_T$ inclusive pion production cross section in proton-proton collisions and present the general formulae for the higher twist differential cross sections in the case of the running coupling and frozen coupling approaches. The structure of infrared renormalon singularities of the higher twist subprocess cross section and the resummed expression (the Borel sum) for it are found. We compared the resummed higher twist cross sections with the ones obtained in the framework of the frozen coupling approximation and leading twist cross section. We obtain, that ratio $R$ for all values of the transverse momentum $p_{T}$ of the pion identical equivalent to ratio $r$. It is shown that the resummed result depends on the choice of the meson wave functions used in calculation. Phenomenological effects of the obtained results are discussed.
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