Phys. Rev. Lett. 80, 3000–3003 (1998)Nonsupersymmetric SU(5) Resuscitated by New Quarks and LeptonsReceived 11 December 1997; published in the issue dated 6 April 1998 The issue of gauge unification in the (nonsupersymmetric) standard model is reinvestigated. It is found that, with just an additional fourth generation of quarks and leptons, SU(3)⊗SU(2)⊗U(1) gauge couplings converge to a common point ∼3.5×1015GeV ( τp∼3.3×1034±2yr). This result is due to the non-negligible, but still perturbative, contributions of the top and fourth generation Yukawa couplings to the gauge two-loop β functions, in contrast with the three generation case where such a contribution is too small to play an important role in unification. © 1998 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.80.3000
DOI:
10.1103/PhysRevLett.80.3000
PACS:
12.10.Kt, 11.10.Hi, 12.10.Dm, 12.60.-i
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