分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-07-05
摘要： We propose a gauged Ud(1)(H) horizontal symmetry around a TeV scale that is a subgroup of a SU(3)(H) horizontal gauge symmetry broken at O(10(14)) GeV. The breaking generates right-handed Majorana neutrino masses through a SU(3)(H) sextet scalar. A particular Majorana right-handed neutrino mass matrix explicitly determines the remnant U(1)(H) at low energy which only couples to b - s and mu - tau in the gauge eigenstate. The dangerous K - (K) over bar, D - (D) over bar mixing and B-s -> mu(+) mu(-) are kept to be safe because the relevant couplings are suppressed through high powers of small mixing angles in the fermion rotation matrix. Our analysis which applies to the general case shows that the Tevatron di-muon anomaly can be explained through the B-s and B-d mixing while keeping all the other experimental constraints within 90% C.L. For the B meson decay, the B-s -> mu(+/-) tau(-/+) is the leading leptonic decay channel which is several orders of magnitude below current experimental bounds.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-07-05
摘要： Recent studies of precision electroweak observables have led to the conclusion that a fourth generation is highly constrained. However, we point out that a long-lived fourth generation can reopen a large portion of the parameter space. In addition, it preserves baryon and lepton asymmetries against sphaleron erasure even if B - L = 0. It opens up the possibility of exact B - L symmetry and hence Dirac neutrinos. The fourth generation can be observed at the LHC with unique signatures of long-lived particles in the near future. (C) 2011 Elsevier B.V. All rights reserved.
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