ar X iv : h ep - p h / 05 11 16 5 v 1 1 4 N ov 2 00 5 GUT angle minimises Z 0 decay
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چکیده
The GUT value of Weinberg’s angle is also the value that minimises the total square matrix elements of Z decay, independently of any GUT consideration, and thus the one that maximises the neutrino branching ratio against total width. We review the proof of this result and some related facts. From any textbook (eg [1]), the amplitude for decay of Z into a fermion pair, at leading order, is Γ(Z → f f̄) = Cf (|Vf | + |Af |) GFM 3 Z 6 √ 2π (1) where Cf is a colour normalisation constant, 1 for fermions and 3 for quarks, and Vf and Af are the vector and axial charges, Vf = T 3 f − 2Qf sin θW (2) Af = T 3 f (3) If we are interested on the decay into a set of fermions, we add the contributions to get the total square matrix element:
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تاریخ انتشار 2005