Charge-changing cross sections have been measured for secondary fragments produced by the interactions of $1.88A$-GeV ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ and $1.82A$-GeV ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ nuclei in Lucite. The cross sections are found to vary by less than 1.5% between 6 and 120 mm from the primary interaction point and are consistent with values expected from the normal reaction cross sections of primary beams. No correlation between secondary and tertiary path lengths has been observed. The present results do not provide supporting evidence for the existence of anomalons.

Fission-neutron angular correlations following fusion of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ and ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ have been measured. Conventional analysis, based on the approximation that post-fission neutrons originate only from fully accelerated fission fragments, gives unexpectedly large numbers of "prefission" neutrons. Comparison with the considerably less fissile system ${}_{}{}^{200}{}_{}{}^{}\mathrm{Pb}$ gives the first convincing evidence that this approach is inadequate. Consideration of neutron emission from the accelerating fragments gives results consistent with expectations.

Current studies of heavy-ion reactions make extensive use of fission-fragment angular distributions to prove the limits of statistical equilibrium. The "standard" theory was derived for a rigid-rotor, transition-state nucleus. Here a more complete theory is developed by inclusion of the dependence of transition-state shape on orientation of the symmetry axis. It is concluded that even this improved application of the liquid-drop model cannot give an adequate prediction of the $\frac{Z^2}{A}$ dependence of fission-fragment anisotropies.

Let $N\mathrm{}\left(Z\right)\mathrm{}$ denote the number of electrons that a nucleus of charge $Z$ binds in nonrelativistic quantum theory. It is proved that $\frac{N\left(Z\right)\mathrm{}}{Z}\to 1$ as $Z\to \infty$. The Pauli principle plays a critical role.

A density-functional formalism comparable to the Hohenberg-Kohn-Sham theory of the ground state is developed for arbitrary time-dependent systems. It is proven that the single-particle potential $v\left(\overrightarrow{\mathrm{r}}t\right)$ leading to a given $v$-representable density $n\left(\overrightarrow{\mathrm{r}}t\right)$ is uniquely determined so that the corresponding map $v\to n$ is invertible. On the basis of this theorem, three schemes are derived to calculate the density: a set of hydrodynamical equations, a stationary action principle, and an effective single-particle Schrödinger equation.

The exact transition temperature, as well as some of the critical exponents, of certain three-dimensional Ising and Potts models is presented. With the analytic results supplemented by assumptions concerning the validity of universality, the critical point is identified as a Liftshitz point. On the basis of hyperscaling, the dynamic exponent $z$ for two-dimensional Ising and Potts model is predicted to be given by $z\nu =2+\alpha$.

There are speculations that grand unified theories (GUT's) may arise from higher-dimensional models of gravity in which the extra dimensions are spontaneously compactified. The GUT predictions for proton decay and ${{sin}^2\theta }_w$ can be significantly modified when nonrenormalizable interactions, scaled by inverse powers of the compactification scale $M_c$, are added to the standard GUT Lagrangian. For example, the decay rate for $p\to e^{+}{\pi }^0$ in minimal SU(5) can be lowered by one (two) orders of magnitude if $M_c$ is on the order of ${10}^{17}$ GeV. However, ${{sin}^2\theta }_w$ then decreases by 0.005 (0.01). The SO(10) model is also discussed.

Magnetic monopoles with multiple Dirac charge are found to be stable in grand unified theories with symmetry breaking by an adjoint Higgs field under certain conditions. In the SU(5) model, the double, triple, quadruple, and sextuple monopoles are stable for a range of parameters in the Higgs potential. The effects of electroweak symmetry breaking on multiply charged monopoles are discussed. Evidence is also presented for the existence of a stable nonspherically symmetric quadruple monopole.

It is shown that, for a wide range of top-quark masses, the Higgs mass in the canonical realization of the Salam-Weinberg theory must be ≲ 125 GeV. The considerations are predicated on the premise that the pure $\lambda {\phi }^4$ theory is a free-field theory. The bound emerges as a necessary condition, albeit within a specific scenario, to avoid the trap of a trivial Higgs sector.

It shown that the chiral model with SU (3) flavor symmetry predicts a dibaryon state of low mass $M\left(M\approx 2.2 \mathrm{GeV}\right)$. It is electrically neutral and is an SU (3) singlet with $J^P=0^{+}$. It corresponds to a six-quark state found in the MIT bag model by Jaffe. It is also shown that there is no stable particlelike state of baryon number 2 which is based on Skyrme's spherically symmetric Ansatz for the chiral field.

The vacuum perturbation produced outside a nucleus which is in the pion-condensed phase is considered within the chiral $\sigma$ model. It is shown that this leads to a quasi long-range pion field outside the nucleus.

Differential cross sections for the pion double-charge-exchange reaction ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}({\pi }^{+},{\pi }^{-}){}_{}{}^{42}{}_{}{}^{}\mathrm{Ti}(\mathrm{g}.\mathrm{s}.\mathrm{})$ have been measured at ${\theta }_{\mathrm{lab}}=5\mathrm{}°$ at several energies. For $T\left({\pi }^{+}\right)<\mathrm{}200\mathrm{}$ MeV, $\sigma \left(5\mathrm{}°\right)$ are found to be more than an order of magnitude larger than those predicted by conventional double-charge-exchange calculations. It is shown that the observed enhancements can be explained in terms of coherent contributions due to terms proportional to ${\rho }^2\mathrm{}\left(r\right)\mathrm{}$ in the pion-nucleus potential whose importance is dramatically enhanced in the presence of large core-excitation components in ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$(g.s.).

Electromagnetic dissociation of ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ target nuclei by the Coulomb field of relativistic heavy ions (RHI) was inferred from measurements of ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}(\mathrm{RHI},X){}_{}{}^{196}{}_{}{}^{}\mathrm{Au}$ cross sections. RHI represents 2.1-GeV/nucleon $p$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, or ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, 1.8-GeV/nucleon ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$, or 1.7-GeV/nucleon ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ projectiles. The experimental cross sections in excess of the estimated nuclear contributions are well described by use of the Weizsäcker-Williams method for calculating the electromagnetic dissociation contributions. Electromagnetic-dissociation calculations are given for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ projectiles at energies expected for the new generation of heavy-ion colliders.

This paper reports the first observation and measurement of two-body ion-neutral association at low temperatures and densities. The rate at 13 K for C${\mathrm{H}}_3^{+}$ + ${\mathrm{H}}_2$ → C${\mathrm{H}}_5^{+}$ + $h\nu$ has been measured to be (1.8 ± 0.3) × ${10}^{-13\mathrm{}}$ ${\mathrm{cm}}^3$/s for a normal (3 to 1) mix of ortho and para hydrogen. The reaction conditions were such that the process could only have proceeded by radiative stabilization of the collision complex.

The formation of beams of triatomic deuterium ${\mathrm{D}}_3$ and the mixed isotopic molecule ${\mathrm{D}}_2$H was optically observed for the first time when the corresponding ions were neutralized by charge exchange. The molecules were detected via the transitions between the Rydberg states $n=3\mathrm{}$ and $n=2\mathrm{}$. An assignment of the ${\mathrm{D}}_2$H spectrum is given. The total lifetimes of rotational sublevels of different electronic states with $n=3\mathrm{}$ of ${\mathrm{D}}_3$ were measured from the radiative decay of molecules along their path behind the charge-exchange region. Agreement with theory is satisfactory.

The Lamb shift in muonium has been measured for the first time by a beam-foil-spectroscopy radio-frequency technique. The value obtained is ${1070}_{-15\mathrm{}}^{+12\mathrm{}}$ MHz, with a systematic uncertainty of 2 MHz, compared with the present theoretical value of 1047.03 MHz.

Muonium in the $2S$ state has been produced by the beam-foil method with a ${\mu }^{+}$ beam of 10 MeV/c. The metastable $2S$ state of muonium has been detected by a static electric field quenching method, and the transition $2S_{\frac{1}{2}}$, $F=1\mathrm{}\to 2P_{\frac{1}{2}}$, $F=1\mathrm{}$ induced by a radio-frequency electric field has been observed with an event rate of about 4/h.

The spatial representation of the generalized potentials associated with the two eigenstates of a quasi-isotropic laser, in the frame of the Landau theory, predicts two different types of first-order phase transitions. The different dynamics of the corresponding vectorial bistabilities are confirmed by an experiment with a laser with two oscillating nondegenerate eigenstates. Polarization instabilities predicted in the first type of transition are experimentally shown.

Pattern competition has been studied experimentally in the free surface modes of a circular fluid layer that is forced vertically. Interaction between nearly degenerate modes of different symmetry gives rise to periodic and chaotic fluctuations. The time-dependent mode amplitudes have been measured with digital imaging methods. Many of the observed phenomena can be explained by a low-dimensional coupled oscillator model that is related to the Navier-Stokes equations.

A scheme for efficiency enhancement in free-electron lasers is described which employs a tapered axial guide field. An analytical description of this process is given in the strong-pump regime. The efficiency enhancement occurs in such a way that the axial velocity remains constant as kinetic energy is extracted from the beam. Results indicate that efficiency enhancements of as much as 100% are possible with only modest gradients in the axial field.