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Abstract: Clean tests of a small admixture of right-handed quark currents directly coupled to the standard W are still lacking. We show that such non-standard couplings can be significantly constrained measuring the value of the scalar Kπ form factor at the Callan–Treiman point to a few percent. A realistic prospect of such a measurement in decay based on an accurate dispersive representation of the scalar form factor is presented. The inadequacy of the currently used linear parametrization is explained and illustrated using recent KTeV data. We briefly comment on the charged kaon mode. [Copyright &y& Elsevier]

Abstract: We calculate the nucleon and the delta mass to fourth order in a covariant formulation of the small scale expansion. We analyze lattice data from the MILC Collaboration and demonstrate that the available lattice data combined with our knowledge of the physical values for the nucleon and delta masses lead to consistent chiral extrapolation functions for both observables up to fairly large pion masses. This holds in particular for very recent data on the delta mass from the QCDSF Collaboration. The resulting pion–nucleon sigma term is . This first quantitative analysis of the quark-mass dependence of the structure of the in full QCD within chiral effective field theory suggests that (the real part of) the nucleon–delta mass-splitting in the chiral limit, , is slightly larger than at the physical point. Further analysis of simultaneous fits to nucleon and delta lattice data are needed for a precision determination of the properties of the first excited state of the nucleon. [Copyright &y& Elsevier]

We consider radiative β-decay of the neutron in heavy baryon chiral perturbation theory, with an extension including explicit Δ degrees of freedom. We compute the photon energy spectrum as well as the photon polarization; both observables are dominated by the electron bremsstrahlung contribution. Nucleon-structure effects not encoded in the weak coupling constants gA and gV are determined at next-to-leading order in the chiral expansion, and enter at the O(0.5%)-level, making a sensitive test of the Dirac structure of the weak currents possible. [Copyright &y& Elsevier]

We present a Lorentz-invariant formulation of baryon chiral perturbation theory including spin-3/2 fields. Particular attention is paid to the projection on the spin-3/2 components of the delta fields. We also discuss the nucleon mass and the pion–nucleon sigma term. [Copyright &y& Elsevier]