Proposals are made predicting the character of longitudinal-momentum distributions in hadron collisions of extreme energies.

From gauge invariance and duality we obtain an exchange degeneracy between $N_{\alpha }$ and $N_{\gamma }$ contributions to pion photoproduction, which is exact for $u=M^2$ but approximate for $u\approx 0$. This may account for the absence of the wrong-signature dip in backward photoproduction.

The transient excitation of molecular vibrations by a picosecond laser-pulse train depends critically on the detailed shape of the exciting pulses. Stokes pulses shorter than or equal to the generating laser pulses have been observed in C${\mathrm{Cl}}_4$. Other aspects of the transient nature include the stimulation of two Stokes lines in methanol and the absence of backward Stokes radiation.

Thermal-conductivity measurements in solid ${\mathrm{He}}^3$ in the bcc phase and at temperatures below about 0.5°K show an unexpected temperature dependence which is less than $T^3$. Specific-heat measurements, in this temperature range, have been reported as showing a closely similar effect, and this provides evidence for a thermal excitation which must take part in the heat transport. In addition, Poiseuille flow of phonons has been directly observed.

Broadening of the free-exciton emission band with increasing excitation intensity is observed in photoluminescence from GaAs. This effect is quantitatively accounted for by electron-exciton collisions.

The electro-optic coefficients ${{\chi }_{E0\mathrm{}}}^{\mathrm{}\left(2\right)\mathrm{}}$ for six III-V compounds InSb, InAs, InP, GaSb, GaAs, and GaP with the zinc-blende structure are calculated using an electrostatic point-charge model. An interpretation of the Faust-Henry result for GaP is presented and an approximate relation is shown to exist between the Faust-Henry coefficient $C$ and the electronic deformation part of the transverse effective charge ${e_T}^{+}$ in these compounds. The case of CuCl is also briefly discussed.

Two- and three-body electrodisintegration cross sections for ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ are calulated with nucleon-nucleon interactions represented by nonlocal, separable forms. Good agreement with experiment is obtained with Tabakin's ground state for the range of incident energies 250 to 550 MeV.

The reactions $\gamma A\to {\pi }^{\pm }{A}^{*}$ have been studied at four-momentum transfers $-t<~0.5$ ${\mathrm{GeV}}^2$ for seven elements ranging from hydrogen to lead. Exclusion-principle suppression is clearly visible at small-momentum transfer. Neither the $A$ dependence nor the energy dependence of the cross sections agrees with the predictions of the vector-dominance model. The ratio of $\frac{{\pi }^{-}}{{\pi }^{+}}$ production requires equal spatial distributions for the protons and neutrons in nuclei. Some $K^{+}$ data are also presented.

Angular distributions in the low-$\mathrm{}\left|t\right|\mathrm{}$ region in the reaction $K^{-}n\to \Lambda {\pi }^{-}$ and in the linereversed reaction ${\pi }^{-}p\to \Lambda K^0$ and from other complementary experiments do not support the predictions of exchange degeneracy between the ${K_{\frac{1}{2}}}^{*}\mathrm{}\left(890\right)\mathrm{}$ and the ${K_{\frac{1}{2}}}^{*}\mathrm{}\left(1420\right)\mathrm{}$ up to $s\sim 11$ ${\mathrm{GeV}}^2$. In the low-$\mathrm{}\left|u\right|\mathrm{}$ region of the reaction $K^{-}n\to \Lambda {\pi }^{-}$ at 3.9 GeV/c, we observe a peak with a slope of 10±3 ${\mathrm{GeV}}^{-2\mathrm{}}$ followed by a valley from $u=-0.15\mathrm{} \mathrm{to} -0.4\mathrm{}$ ${\mathrm{GeV}}^2$. A simple Regge-pole fit to this backward-scattering region using the $N_{\alpha }$ trajectory is presented.

Evidence for a destructive interference effect between the ${\rho }^0$ and $\omega \to {\pi }^{+}{\pi }^{-}$ amplitudes has been observed in the channel ${\pi }^{+}p\to {\pi }^{+}{\pi }^{-}{\Delta }^{++}$ at 3.7-4.0 GeV/c. On the assumption of complete coherence between the ${\rho }^0$ and $\omega \to {\pi }^{+}{\pi }^{-}$ amplitude in a subsample, discussed in the text, a branching ratio $\frac{(\omega \to {\pi }^{+}{\pi }^{-})}{(\omega \to {\pi }^{+}{\pi }^{-}{\pi }^0)}=1.5\%$ is obtained with a 95% confidence-level lower limit of 0.25%. The data do not lead to a significant upper limit. In terms of $\delta$, the off-diagonal element of the ${\rho }^0\omega$ mass-mixing matrix, these values are equivalent to $\delta =2.7\mathrm{}$ MeV and a lower limit of 1.1 MeV. Under conditions stated in the text, a value $\beta =1.5\mathrm{}\pm 0.3$ rad is obtained for the production phase of ${\rho }^0$ relative to $\omega$ in the channel studied.

The interpretation of the results of Cairns, McCusker, Peak, and Woolcott, indicating a discovery of quarks in the cores of very energetic extensive air showers, is shown to be extremely difficult to reconcile with the results of other negative experiments. Alternative explanations of their results are then suggested.

Very high-energy cosmic rays, on emerging from their places of origin, are subject to photodisintegration and energy degradation by blue-shifted photons. It is shown that the intense photon fields of supernova explosions, of quasistellar objects, and of one of the current pulsar models are able to cause complete disintegration of complex nuclei and significant energy losses of protons at energies consistent with observed changes in the cosmic-ray charge and energy spectrum, respectively.

We construct local quantum fields in two dimensions with a scalar Yukawa interaction. The corresponding Hamiltonian has two ultraviolet-divergent renormalization constants.

Utilizing a simple field-theoretic model, we consider the production of timelike muon pairs via a massive virtual photon in high-energy hadronic collisions. We predict the differential cross section in the squared mass of the muon pair as well as the total cross section. We find that our form factors do not possess the analog of the Bjorken scaling associated with deep inelastic electron scattering, but are scale functions multiplied by the usual bremsstrahlung factor $\frac{〈t_{\mathrm{av}}〉}{s}$.

A continued factorization method is introduced to establish upper and lower bounds on the dynamic polarizability of both real and imaginary frequencies. It converges rapidly and has a wider frequency range of applicability than other methods.

The $2{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}-2\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ separation $\Delta E-\mathcal{S}$ in hydrogen has been measured by a microwave atomic-beam technique. The result obtained from four independent transitions is $\Delta E-\mathcal{S}=9911.173\mathrm{}\pm 0.042$ MHz. We combine this result with the recent determination of the Lamb shift $\mathcal{S}$ by Robiscoe to obtain a value for the fine-structure splitting $\Delta E$ and a value for the fine-structure constant ${\alpha }^{-1\mathrm{}}=137.0358\mathrm{}\left(5\right)\mathrm{}$.

The reduction in superfluid mass of helium contained in restricted geometries has been studied as a function of temperature. The results are discussed in terms of a superfluid healing length ${\xi }_s$. Near $T_{\lambda }$, ${\xi }_s$ can be described by a power law, ${\xi }_s={\xi }_{s,0\mathrm{}}{(1-\frac{T}{T_{\lambda }})}^{-\nu }$, where $\nu =0.67\mathrm{}\pm 0.04$. A value for ${\xi }_{s,0\mathrm{}}=4.0\mathrm{}\pm 0.5$ Å is obtained from the analysis of superfluid flow through a slit of known geometry.

Profiles of the He II 4686- and 3203-Å lines observed during the passage of the imploding current sheath in a high-velocity, low-density $\theta$ pinch show a broadening that at early times is not due to the usual mechanisms (Doppler, Holtsmark, or Zeeman effects). Most of this broadening is therefore interpreted as due to Stark effects caused by suprathermal collective field fluctuations, and at later times as due to a combination of these and Doppler effects.

We have used a standing wave technique to measure the velocity of ≈1-kHz sound waves in C${\mathrm{O}}_2$ near its critical point along critical and near-critical isochores. The measurements indicate the existence of a logarithmic divergence over several decades in $T-T_c$ for the adiabatic compressibility and the specific heat at constant volume along the critical isochore.

In computer-experimental studies of surface vibrations in monatomic crystals, surface modes of a new type have been found near the Brillouin zone boundary in gaps between bands of different kinds of bulk modes (e.g., longitudinal and transverse). Other surface modes, including Rayleigh waves and extra high- or low-frequency modes when adsorbed films are present, have also been found and investigated.