分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-07-05
摘要： The improved standard model prediction for total top quark forward-backward asymmetry of 8.9% at the Tevatron has significantly reduced the long-term discrepancy between the theory value and the experimental observations. The seemingly "last" over-3 sigma anomaly is the CDF measurement of A(FB)(M-t (t) over bar > 450 GeV) and it is not seen by the D0 Collaboration. In this paper, we take the CDF measurement to obtain the best-fit parameter space for various previously proposed models, including axigluon, t-channel neutral current, charged current, and diquark models, then study the predictions of the corresponding parameter space on the direct search or indirect constrain. The particular axigluon model is excluded by the LHC dijet search. The t-channel Z' model suffer from the Tevatron same-sign dilepton search bound. The t-channel W' model and the diquark model both predict significant increase in the production rate of inclusive t (t) over bar search at the LHC which is not seen. We conclude none of the models are favored by the direct search bound.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-06-30
摘要： We construct a general class of pseudo-Goldstone composite Higgs models, within the minimal SO(5)/SO(4) coset structure, that are not necessarily of moose-type. We characterize the main properties these models should have in order to give rise to a Higgs mass around 125 GeV. We assume the existence of relatively light and weakly coupled spin 1 and 1/2 resonances. In absence of a symmetry principle, we introduce the Minimal Higgs Potential (MHP) hypothesis: the Higgs potential is assumed to be one-loop dominated by the SM fields and the above resonances, with a contribution that is made calculable by imposing suitable generalizations of the first and second Weinberg sum rules. We show that a 125 GeV Higgs requires light, often sub-TeV, fermion resonances. Their presence can also be important for the models to successfully pass the electroweak precision tests. Interestingly enough, the latter can also be passed by models with a heavy Higgs around 320 GeV. The composite Higgs models of the moose-type considered in the literature can be seen as particular limits of our class of models.
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