We examine the effects of SU͑3͒ breaking in the matrix elements of the flavor-diagonal axial-vector currents between octet baryon states. Our calculations of K, , and loops indicate that the SU͑3͒ breaking may be substantial for some matrix elements and at the very least indicate large uncertainties. In particular, the strange axial matrix element in the proton determined from the measurements of g 1 (x) is found to have large uncertainties and might yet be zero. We estimate the strange axial matrix element in the proton to be Ϫ0.35Շ⌬sՇ0 and the matrix element of the flavor-singlet current in the proton to be Ϫ0.1Շ⌺Շϩ0.3 from the E143 measurement of ͐dxg 1 (x)ϭ0.127Ϯ0.004Ϯ0.010. The up-quark content of the ⌶ Ϫ is discussed and its implications for nonleptonic weak processes discussed. We also estimate the matrix element of the axialvector current coupling to the Z 0 between all octet baryon states. This may be important for neutrino interactions in dense nuclear environments, where hyperons may play an important role. ͓S0556-2821͑97͒00709-1͔ PACS number͑s͒: 12.15. Ji, 12.39.Fe, 14.20.Dh One of the more exciting realizations in hadronic physics of the last few years is that the strange quark may play an important role in the structure of the nucleon ͓1͔. While this may seem somewhat unnatural in the context of the most naive quark model, it is perfectly natural from the standpoint of QCD. Matrix elements of the strange vector current must vanish at zero-momentum transfer between states with zero net strangeness; however, matrix elements of the axial-vector current need not. Recent measurements suggest that the matrix element of the strange axial-vector current in the proton is ⌬sϭϪ0.12Ϯ0.04 ͓2͔. In addition, one would like to know what fraction of the nucleon spin is carried by the quarks themselves, which is equivalent to determining the matrix element of flavor-singlet axial-vector current in the proton ⌺. This is, of course, intimately related to the matrix element of the strange axial-vector current and present analysis suggests that ⌺ϭ0.2Ϯ0.1 ͓2͔, much smaller than the quark model estimate of ⌺ϳ0.58. There have been intense theoretical and experimental efforts to extract ⌬s and ⌺ to address the present ''spin crisis'' and such efforts continue ͑for recent reviews, see ͓3,4͔͒.A vital ingredient in the present determination of ⌺ and ⌬s is the matrix element of the j 5 ,8 ϭū␥ ␥ 5 uϩd␥ ␥ 5 d Ϫ2s␥ ␥ 5 s axial-vector current in the nucleon, which cannot be measured directly but must be inferred from the approximate SU͑3͒ symmetry observed in nature. The question of SU͑3͒ breaking in the matrix element of the j 5 ,8 current and its impact upon the extraction of ⌬s and ⌺ has been previously addressed ͓5-10͔. In ͓5,6͔ it was assumed that the breaking in the matrix elements of the axial-vector currents was proportional to the breaking in the octet baryon masses and in ͓7͔ a model of the SU͑3͒ breaking was employed. Studies in the Skyrme model ͓9͔ suggest that ⌺ is relatively insensitive to SU͑3͒ breaking while ⌬s sh...
Using chiral perturbation theory we calculate the imaginary parts of the K L → ϩ Ϫ e ϩ e Ϫ form factors that arise from → ϩ Ϫ and → ϩ Ϫ ␥* rescattering. We discuss their influence on CP-violating variables in K L → ϩ Ϫ e ϩ e Ϫ .
We investigate the relations that must hold among baryonic Isgur–Wise functions ηi in the large-Nc limit from unitarity constraints, and compare to those found by Chow using the Skyrme model [or SU(4)]. Given the exponential dropoff of the ηi away from threshold, unitarity requires only that the usual normalization conditions hold at w=1, and that η=η1 near threshold. Our results are consistent with, but less powerful than, the Skyrme model relations. This shows that large-Nc analyses comprise more than just unitarity constraints.
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