PDF《AXIONS》

2008 10:42 C 5C Hadronic axions do not couple to ordinary quarks and leptons at tree level. In the DFSZ model [14], the coupling coe?cient to electrons is Ce = cos2 β

3 , (8) where tan β is the ratio of two Higgs vacuum expectation values that are generic to this and similar models. The nucleon couplings Cn,p are related to nucleon axial- vector current matrix elements by generalized Goldberger- Treiman relations, Cp = (Cu ? η)?u + (Cd ? ηz)?d + (Cs ? ηw)?s , Cn = (Cu ? η)?d + (Cd ? ηz)?u + (Cs ? ηw)?s . (9) Here, η = (1+z +w)?1 with z = mu/md and w = mu/ms z. ?q represents the axial-vector current couplings to the proton by ?q S? = p|? qγ?γ5q|p , where S? is the proton spin. Neutron beta decay and strong isospin symmetry considera- tions imply ?u??d = F +D = 1.267±0.0035, whereas hyperon decays and ?avor SU(3) symmetry imply ?u + ?d ? 2?s = 3F ? D = 0.585 ± 0.025. The strange-quark contribution is ?s = ?0.08 ± 0.01stat ± 0.05syst from the COMPASS experi- ment [18], and ?s = ?0.085 ± 0.008exp ± 0.013theor ± 0.009evol from HERMES [19], in agreement with each other and with an early estimate of ?s = ?0.11 ± 0.03 [20]. We thus adopt ?u = +0.841 ± 0.020 , ?d = ?0.426 ± 0.020 , ?s = ?0.085 ± 0.015 , (10) which are very similar to what was used in the axion literature. The uncertainty of the axion-nucleon couplings is dominated by the uncertainty z = 0.3C0.6 that we mentioned earlier. For hadronic axions Cu,d,s = 0, so that Cp = ?0.55 and Cn = +0.14, if z = 0.3 and Cp = ?0.37 and Cn = ?0.05 if z = 0.6. While it is well possible that Cn = 0, Cp does not vanish within the plausible z range. In the DFSZ model, Cu =

1 3 sin2 β and Cd =

1 3 cos2 β. Even with the large zCuncertainty, Cn and Cp never vanish simultaneously. An extreme case is cos2 β = 0........