A low-energy theorem is derived for the structure-dependent axial-vector form factor in the radiative decay $\pi \to l\nu \gamma$ using current-algebra techniques. By saturation of the sum rule with a few low-lying resonances, an estimate is made which is compared with experiments.

Assuming that the weak interactions are mediated by vector bosons, it is shown that the divergent parts of the second-order electromagnetic corrections to $\mu$ and $\beta$ decays are identical in the limit of zero momentum transfer to the leptons. Therefore, in such a case the corrections to $\frac{G_V}{G_{\mu }}$ are finite. Implications of this result for the space-space part of the current algebra are briefly discussed.

We report preliminary results of an experiment designed to compare the collisionless damping of small- and large-amplitude plasma waves.

The superconductive transition temperatures $T_c$ of single-crystal specimens of reduced strontium titanate have been measured as functions of hydrostatic and uniaxial compressional stresses up to 1.5 kbar. The prominent features of the experimental results are a large, nonlinear, hydrostatic-pressure effect and an anisotropic uniaxial stress effect. The relative decrease of transition temperature with pressure $\frac{\Delta \left(\ln T_c\right)}{\Delta p}$ is about an order of magnitude larger than that seen in metallic superconductors.

We have measured in-plane and out-of-plane ferromagnetic resonance linewidths of single-crystal Ni platelets at 25.92 and 9.42 GHz. It is observed that the intrinsic linewidth of these samples is anisotropic at 25.92 GHz, exhibiting cubic crystalline anisotropy rather than the geometrical symmetry of the sample. We propose that the anisotropic part of the intrinsic linewidth is due to direct relaxation of the magnetic energy to the lattice.

It is pointed out that the vanishing of the wave-function renormalization constant associated with a field operator $\Phi$ is not implied by the existence of a representation of $\Phi$ as a weak limit of a nonlocal product of other fields.

It is argued, on experimental grounds, that Weinberg's second sum rule must be abandoned for vector-current spectral functions as long as the vector-meson dominance approximation is qualitatively valid.

Suitable linear combinations of the $N-N$ helicity amplitudes are constructed to eliminate the contribution of the deuteron and the virtual singlet trajectories. Thus four out of the five independent and crossing-odd $N-N$ scattering amplitudes are shown to be superconvergent. However, the pseudoscalar-, scalar-, and vector-meson contributions fail to saturate most of these superconvergence relations.