Physics – Nuclear Physics – Nuclear Theory
Scientific paper
2001-05-18
Phys.Rev. C64 (2001) 028201
Physics
Nuclear Physics
Nuclear Theory
6 pages, 1 figure, to be published in Physical Review C (brief report)
Scientific paper
10.1103/PhysRevC.64.028201
Present precision measurements of the neutron life time lead to a CKM matrix element $|V_{ud}|$ which is three standard deviations off the value inferred from heavy quark decays etc. We investigate the possibility whether isospin-breaking effects in the neutron-to-proton vector current transition matrix element $< p|V^+_0|n >=1+\delta g_V$ could eventually close this gap. For that we calculate in chiral perturbation theory the effect of pion and kaon loops on the matrix element $< p|V^+_0|n >$ taking into account the mass differences of the charged and neutral mesons. We find a negligibly small isospin-breaking effect of $\delta g_V \simeq -4 \cdot 10^{-5}$. The crucial quantity in the analysis of neutron beta-decay precision measurements is thus the radiative correction term $\Delta_R$. Furthermore, we calculate in heavy baryon chiral perturbation theory the SU(3) breaking effects on the vector transition charges of weak semi-leptonic hyperon decays. We find for these quantities channel-dependent relative deviations from the SU(3) limit which range from -10% to $+1%$.
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