Radiative Corrections and the Universality of the Weak Interactions

We review the radiative corrections to superallowed Fermi transitions and neutron beta decay in the Standard Model, and their relevance for the universality of the Weak Interactions.Comment: 5 pages. Invited talk at 8th Conference on the Intersections of Particle and Nuclear Physics (CIPANP 2003), New York, New York, 19-24 May 200

Considerations concerning the generalization of the Dirac equations to unstable fermions

We discuss the generalization of the Dirac equations and spinors in momentum space to free unstable spin-$1/2$ fermions taking into account the fundamental requirement of Lorentz covariance. We derive the generalized adjoint Dirac equations and spinors, and explain the very simple relation that exists, in our formulation, between the unstable and stable cases. As an application of the generalized spinors, we evaluate the probability density. We also discuss the behavior of the generalized Dirac equations under time reversal.Comment: 7 pages, matches journal versio

Improved Calculation of Electroweak Radiative Corrections and the Value of V_ud

A new method for computing hadronic effects on electroweak radiative corrections to low-energy weak interaction semileptonic processes is described. It employs high order perturbative QCD results originally derived for the Bjorken sum rule along with a large N QCD-motivated interpolating function that matches long and short-distance loop contributions. Applying this approach to the extraction of the CKM matrix element V_ud from superallowed nuclear beta decays reduces the theoretical loop uncertainty by about a factor of 2 and gives V_ud = 0.97377(11)(15)(19). Implications for CKM unitarity are briefly discussed.Comment: 12 pages, no figures. Ref. [8] correcte