Saving fourth generation and baryon number by living long

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.