At the beginning of the 1970s there seemed little reason to believe that strangeness-conserving neutral currents existed: theoreticians had no pressing need for them and several experiments suggested that they were suppressed if they were present at all. Indeed the two remarkable neutrino experiments that eventually led to their discovery were designed and built for very different purposes, including the search for the vector boson and the investigation of the parton model. In retrospect we know that certain gauge theories (notably the Weinberg-Salam model) predicted that neutral currents exist. But until 't Hooft and Veltman proved that such theories were renormalizable, little effort was made to test the new theories. After the proof the two experimental groups began to reorient their goals to settle an increasingly central issue of physics. Do neutral currents exist? We ask here: What kind of evidence and arguments persuaded the participants that they had before them a real effect and not an artifact of the apparatus? What eventually convinced them that their experiment was over? An answer to these questions requires an examination of the organization of the experiments, the nature of the apparatus, and the previous work of the experimentalists. Finally, some general observations are made about the recent evolution of experimental physics.

The need for reexamination of the standard model of strong, weak, and electromagnetic interactions is discussed, especially with regard to 't Hooft's criterion of naturalness. It has been argued that theories with fundamental scalar fields tend to be unnatural at relatively low energies. There are two solutions to this problem: (i) a global supersymmetry, which ensures the absence of all the naturalness-violating effects associated with scalar fields, and (ii) composite structure of the scalar fields, which starts showing up at energy scales where unnatural effects would otherwise have appeared. With reference to the second solution, this article reviews the case for dynamical breaking of the gauge symmetry and the technicolor scheme for the composite Higgs boson. This new interaction, of the scaled-up quantum chromodynamic type, keeps the new set of fermions, the technifermions, together in the Higgs particles. It also provides masses for the electroweak gauge bosons $W^{\pm }$ and $Z^0$ through technifermion condensate formation. In order to give masses to the ordinary fermions, a new interaction, the extended technicolor interaction, which would connect the ordinary fermions to the technifermions, is required. The extended technicolor group breaks down spontaneously to the technicolor group, possibly as a result of the "tumbling" mechanism, which is discussed here. In addition, the author presents schemes for the isospin breaking of mass matrices of ordinary quarks in the technicolor models. In generalized technicolor models with more than one doublet of technifermions or with more than one technicolor sector, we have additional low-lying degrees of freedom, the pseudo-Goldstone bosons. The pseudo-Goldstone bosons in the technicolor model of Dimopoulos are reviewed and their masses computed. In this context the vacuum alignment problem is also discussed. An effective Lagrangian is derived describing colorless low-lying degrees of freedom for models with two technicolor sectors in the combined limits of chiral symmetry and large number of colors and technicolors. Finally, the author discusses suppression of flavor-changing neutral currents in the extended technicolor models.

For plasma with a large number of degrees of freedom, particle simulation using high-speed computers can offer insights and information that supplement those gained by traditional experimental and theoretical approaches. The technique follows the motion of a large assembly of charged particles in their self-consistent electric and magnetic fields. With proper diagnostics, these numerical experiments reveal such details as distribution functions, linear and nonlinear behavior, stochastic and transport phenomena, and approach to steady state. Such information can both guide and verify theoretical modeling of the physical processes underlying complex phenomena. It can also be used in the interpretation of experiments.

This review covers in great detail the Bethe-ansatz approach to the solution of various versions of the Kondo problem.

The present status of high-pressure research with the diamond anvil cell (DAC) is reviewed in this article, mainly from an experimental aspect. After a brief description of the different types of DAC's that are currently in vogue, the techniques used in conjunction with the DAC in modern high-pressure research are presented. These include techniques for low- and high-temperature studies, x-ray diffractometry, spectroscopy with the DAC, and other measurements. Results on selected materials, with a view to illustrating the physics behind high-pressure phenomena, are presented and discussed. These include metal-semiconductor transitions, electronic transitions, phonons and high-pressure lattice dynamics, and phase transitions. A whole section is devoted to the behavior of condensed gases, principally ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, ${\mathrm{O}}_2$, ${\mathrm{N}}_2$, and rare-gas solids. The concluding section briefly deals with speculations on ultra-high-pressure research with the DAC in the future.

The authors review the theory and the empirical evidence of damping of simple nuclear excitations. The excitations considered are the particle states and vibrational states. The particle damping phenomena include the fragmentation of single-particle levels, the systematics of neutron strength functions, and the optical absorption of elastic scattering. Information on the known collective vibrational states is summarized and compared with theory. A theoretical model that has found considerable success is based on a damping mechanism in which the simple excitations mix with the surface vibrations. This implies that the surface damping dominates for excitation energies below about 15 MeV. There is a close relation between the single-particle damping and the damping of collective vibrations. However, the vibrational damping is strongly suppressed by the coherence between the particle and the hole. While the model reproduces many of the observed features of the data rather well, it tends to underpredict the spreading width by as much as a factor of 2. Thus other degrees of freedom, not well understood at present, may play a role in the damping.

Quantum-mechanical phase-space distributions, introduced by Wigner in 1932, provide an intuitive alternative to the usual wave-function approach to problems in scattering and reaction theory. The aim of the present work is to collect and extend previous efforts in a unified way, emphasizing the parallels among problems in ordinary quantum theory, nuclear physics, chemical physics, and quantum field theory. The method is especially useful in providing easy reductions to classical physics and kinetic regimes under suitable conditions. Section II, dealing in detail with potential scattering of a spinless nonrelativistic particle, provides the background for more complex problems. Following a brief description of the two-body problem, the authors address the $N$-body problem with special attention to hierarchy closures, Boltzmann-Vlasov equations, and hydrodynamic aspects. The final section sketches past and possibly future applications to a wide variety of problems.

The review consists of two major parts. In the first part, several calculable $R$-matrix and related theories are described and discussed. These include the Kapur-Peierls, Wigner-Eisenbud, calculable standard $R$-matrix, extended $R$-matrix, finite-element, natural boundary condition, and variational methods. The various approaches are critically compared using four selected applications: (i) exactly soluble model using two coupled square-well potentials, (ii) elastic scattering of neutrons from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, (iii) elastic scattering of electrons from He atoms, and (iv) $\alpha -\alpha$ elastic scattering. In the second part, the Baer, Kouri, Levin, and Tobocman many-body scattering theory is reviewed. The principal results of the theory are derived, and a survey of calculations applying the theory is presented. The derivation is carried out in the context of the $R$-matrix method wherein the many-body scattering is treated ab initio as a steady-state process. This has the advantage that the channel states form a complete orthogonal set. These same channel states are used to provide explicit representations of the partition Green's-function operators.

A thorough unified treatment is given of the quantum-mechanical operators and wave functions for a molecular system (composed of $N$ moving charged particles) in static uniform electric and magnetic fields $\mathit{E}$ and $\mathit{B}$. The treatment is rigorous within the nonrelativistic approximation. The system may either be neutral or charged. The fields may have arbitrary intensities and orientations. Close correspondence is maintained between the classical and quantum-mechanical treatments. The wave functions are expressed both in the time-independent energy representation and in time-dependent wave packets. Three types of momentum play important roles. For single-particle systems they are the canonical momentum $\mathit{P}$, the mechanical momentum $\mathit{\Pi }=\mathit{P}-\left(\frac{e}{c}\right)\mathit{A}=M\dot{R}$, and the pseudomomentum $\mathcal{K}=\mathit{\Pi }-\left(\frac{e}{c}\right)\mathit{R}\times \mathit{B}-e\mathit{E}t$. The pseudomomentum is a constant of the motion. Except in the absence of magnetic fields, not all of the components of either $\mathit{\Pi }$ or $\mathcal{K}$ commute. This complicates the quantum-mechanical formalism. The components of the pseudomomentum have simple classical interpretations, and in quantum mechanics they are related to the operator which performs a boost to a reference frame moving with constant velocity $\mathit{v}$. In this moving frame, the electric field intensity is ${\mathit{E}}^{\prime }=\mathit{E}+\left(\frac{\mathit{v}}{c}\right)\times \mathit{B}$. Thus, in a frame moving with the drift velocity ${\mathit{v}}_d=\left(\frac{c}{B^2}\right)\mathit{E}\times \mathit{B}$, the components of the electric field intensity perpendicular to $\mathit{B}$ vanish. In this paper, the velocity boost operators are used to show the relationships between wave functions expressed in reference frames moving with repsect to each other. The dynamics of the $N$-particle systems are simplified by making the Power-Zienau-Woolley transformation (which reduces as a special case to a unitary transformation used by Lamb) and by using center-of-mass and internal coordinates. Generalizing previous works, it is shown how the pseudomomentum is involved in separating these degrees of freedom for $N$ particles in both $\mathit{E}$ and $\mathit{B}$. For neutral molecules, the Schrödinger equation is "pseudoseparated" and the internal degrees of freedom are coupled to the center of mass motion only by the "motional Stark Effect," which involves the constant of motion $\mathcal{K}$. For ionic systems, only one component of the center of mass is coupled to the internal motion. Quantitative estimates of the weak center-of-mass coupling are made for both neutral and ionic $n=1\mathrm{}$ and $n=2\mathrm{}$ quantum states of two-body systems by perturbation expansions in powers of the field strengths. In the usual nonrigorous treatments of systems in magnetic fields, no distinction is made between $\mathit{\Pi }$ and $\mathcal{K}$ and both are approximated by $M\dot{R}$, where $M$ is the mass of the molecule and $\mathit{R}$ is taken to be the classical orbital position of a single particle having the same mass and charge. This is an excellent approximation for ground-state molecules and ions in weak fields. However, the resulting errors can be much larger if the system is in either intense fields or high-lying states (e.g., Rydberg levels). These are the conditions under which the rigorous formalism should be most useful. The determination of the wave functions and energy levels for many-particle ionic systems is complicated due to the coupling with the center of mass. The suggestion is made that it might be useful to boost the reference frame so that it moves with the velocity $\dot{R}$ of a single classical particle. The Schrödinger equation in this frame could serve as a more suitable basis for perturbative or variational treatments.

The theory of magnetism in solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is reviewed with emphasis on the multiple-spin-exchange theory of the magnetic interaction. Critical experiments are discussed briefly, and the most reliable present values for various quantities are chosen. Various theories of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ magnetism are considered, with the conclusion that multiple particle exchange is the most likely mechanism. The microscopic theory of exchange is presented mainly from the standpoint of tunneling ducts. The spin Hamiltonian which results from two-, three-, and four-particle ring exchange is derived and studied in the high-temperature limit, in mean-field approximation, and with spin waves. Two reasonable parameter sets are selected which fit the experimental data, with the conclusion that the exchanges are mainly three- and four-particle rings. A discussion is given of remaining problems together with some conjectures.

The physical and theoretical foundations are presented for the mean-field theory of nuclear structure and dynamics. Salient features of the many-body theory of stationary states are reviewed to motivate the time-dependent mean-field approximation. The time-dependent Hartree-Fock approximation and its limitations are discussed and general theoretical formulations are presented which yield time-dependent mean-field equations in lowest approximation and provide suitable frameworks for overcoming various conceptual and practical limitations of the mean-field theory. Particular emphasis is placed on recent developments utilizing functional integral techniques to obtain a quantum mean-field theory applicable to quantized eigen-states, spontaneous fission, the nuclear partition function, and scattering problems. Applications to a number of simple, idealized systems are presented to verify the approximations for solvable problems and to elucidate the essential features of mean-field dynamics. Finally, calculations utilizing moderately realistic geometries and interactions are reviewed which address heavy-ion collisions, fusion, strongly damped collisions, and fission.

The radio line emission of interstellar molecules routinely shows deviations from thermal equilibrium which culminate with strong maser radiation in some sources. Like its laboratory counterpart, the maser radiation is amplified through the effect of induced processes in a region where a population inversion exists and displays many of the basic features of laboratory lasers. This review is intended to explain the basic theory of astronomical masers and to survey the theoretical models which were developed for specific sources.

Since the heroic era of Baade and Zwicky, our understanding of supernovae has advanced in hops and skips rather than steadily. The most recent jump has been into fairly general agreement that observations of Type I's can be interpreted as the manifestation of the decay of about $1M_{\odot }$ of ${\mathrm{Ni}}^{56}$ and observations of Type II's as the manifestation of ≳${10}^{51}$ ergs deposited at the bottom of a supergiant envelope by core bounce as a central neutron star forms. This paper explores the history of these and other ideas of what is going on in supernovae, the presupernova evolution of the parent stars and binary systems, observed properties of the events, and models for them. A later paper (Part II: the aftermath) will address the results of supernovae—their remnants, production of cosmic rays and gamma rays, nucleosynthesis, and galactic evolution—and the future of supernova research.

The effect of neutral nonresonant collisions on the shape, shift, and intensity of atomic spectral-line profiles is reviewed. A general treatment for the study of an atomic spectral line is developed by establishing reasonable assumptions about the relevant collision processes and by finding an expression for the Fourier transform of the line profile. The authors look at parallel developments of other methods of calculation, consider special limits of practical interest, and illustrate numerical evaluations of complete line profiles. Interatomic potentials for use in line-profile calculations are described, and the problems imposed by nonadditivity and nonadiabaticity are also noted. The observation of line profiles by both conventional and tunable-laser techniques is surveyed. Representative experimental measurements of the widths and shifts of collision-broadened spectral line cores are tabulated, and the phenomena of satellites, oscillations, and power-law behavior of line wings are compared with theoretical expectations. The use of experimental results for the determination of excited atom-atom interactions, the prediction of collision broadening in stellar atmospheres, and the effect of foreign gases on laboratory standard wavelengths are also discussed.

A review is given of recent theoretical studies devoted to the problem of generating radiation fields that exhibit the opposite of the well-known bunching of photons observed in light from thermal sources, the so-called antibunching effect. It is made clear that this phenomenon reflects the corpuscular nature of light and, hence, cannot be interpreted in terms of classical electrodynamics, needing, instead, the quantum-mechanical formalism for its description. It is shown in some detail that nonlinear interaction mechanisms like multiphoton absorption and parametric three-wave interaction are suited to change the photon statistical properties of incident (in most cases coherent) light such that the output field will be endowed with antibunching properties. Special emphasis is given to the problem of correctly specifying the dimensions of the mode volume occurring in the usual single-mode treatment of the field, which is, in fact, of great practical interest, since the magnitude of the antibunching effect is determined by the inverse average number of photons contained in that volume. In a later section it is pointed out that destructive interference with a coherent reference beam provides a means of (a) effectively enhancing photon antibunching that is already present in a high-intensity field, through reduction of the intensity, and (b) transforming phase fluctuations produced in a Kerr medium into antibunching-type intensity fluctuations. On the other hand, there exists a way of directly generating light with antibunching properties, the physical mechanism being resonance fluorescence from a single atom. The main features of this technique, both theoretical and experimental, are outlined, including a discussion of the first experimental results obtained a few years ago.

Classical and degenerate, strongly coupled plasmas are approached by computer simulations, analytic theories, and variational methods. Thermodynamic properties predicted in those various approaches are compared and examined; possibilities of Wigner crystallization and other instabilities are investigated. Salient features in the static and dynamic correlations are reviewed. Screening effects are analyzed and applied to calculations of the enhancement factor of the thermonuclear reaction rate and the electric resistivity in dense plasmas. Theoretical predictions on the dynamic properties are compared with the x ray and electron scattering data for the metallic electrons.

Ideal magnetohydrodynamic theory and its application to magnetic fusion systems are reviewed. The review begins with a description and derivation of the model as well as a discussion of the region of validity. Next, the general properties are derived which are valid for arbitrary geometry and demonstrate the inherently sound physical foundation of the model. The equilibrium behavior of the currently most promising toroidal magnetic fusion concepts are then discussed in detail. Finally, the stability of such equilibria is investigated. Included are discussions of the general stability properties of arbitrary magnetic geometries and of detailed applications to those concepts of current fusion interest.

The uncertainties that affect the prediction of solar neutrino fluxes are evaluated with the aid of standard solar models. The uncertainties are determined from available data for all measured quantities that are known to affect significantly the neutrino fluxes; these include nuclear reaction rates, the solar constant, and the primordial surface composition of the sun. Uncertainties in theoretical quantities (such as the stellar opacity, the equation of state, and the rate of the proton-proton reaction) are estimated from the range of values in published state-of-the-art calculations. The uncertainty in each neutrino flux that is caused by a specified uncertainty in any of the parameters is evaluated with the aid of a series of standard solar models that were constructed for this purpose; the results are expressed in terms of the logarithmic partial derivative of each flux with respect to each parameter. The effects on the neutrino fluxes of changing individual parameters by large amounts can usually be estimated to satisfactory accuracy by making use of the tabulated partial derivatives. An overall "effective $3\sigma$ level of uncertainty" is defined using the requirement that the true value should lie within the estimated range unless someone has made a mistake. Effective $3\sigma$ levels of uncertainty, as well as best estimates, are determined for the following possible detectors of solar neutrinos: ${}_{}{}^2{}_{}{}^{}\mathrm{H}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$, ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$, ${}_{}{}^{79}{}_{}{}^{}\mathrm{Br}$, ${}_{}{}^{81}{}_{}{}^{}\mathrm{Br}$, ${}_{}{}^{97}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{98}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$, and electron-neutrino scattering. The most important sources of uncertainty in the predicted capture rates are identified and discussed for each detector separately. For the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ detector, the predicted capture rate is 7.6±3.3 (effective $3\sigma$ errors) SNU. The measured production rate is (Cleveland, Davis, and Rowley, 1981) 2.1±0.3 SNU ($1\sigma$ error). For a ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ detector, the expected capture rate is 106 ($1_{-0.08\mathrm{}}^{+0.12\mathrm{}}$) SNU (also effective $3\sigma$ errors). The relatively small uncertainty quoted for the ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ detector is a direct result of the fact that ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ is primarily sensitive to neutrinos from the basic proton-proton reaction, the rate of which is determined largely by the observed solar luminosity. The Caltech and Munster measured values for the cross-section factor for the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}$($\alpha$,$\gamma$)${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ are inconsistent with each other. The capture rates quoted above were obtained using the Caltech value for the cross-section factor. If the Munster value is used instead, then the predicted capture rate for the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ experiment is 4.95±2.1 SNU (effective $3\sigma$ errors) and, for the ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ga}$ experiment, 96.7 ($1_{-0.08\mathrm{}}^{+0.12\mathrm{}}$) SNU (effective $3\sigma$ errors). In order for the best-estimate value to agree with the observation of Davis (1978) of 2 SNU for the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ experiment, the cross-section factor $S_{34}\mathrm{}\left(0\right)\mathrm{}$ would have to be reduced by about $15\sigma$ to less than the Caltech value, i.e. to $7\sigma$ less than the Munster value. The characteristics of the standard solar model, constructed with the best available nuclear parameters, solar opacity, and equation of state, are presented in detail. The computational methods by which this and similar models were obtained are also described briefly. The primordial helium abundance inferred with the aid of standard solar models is $Y=0.25\mathrm{}\pm 0.01$. The complementary relation between observations of solar neutrinos and of the normal modes of oscillation of the sun is examined. It is shown that the splitting of the observed large-$n$, small-$l$, $p$-mode (five minute) oscillations of the sun primarily originates in the outer ten percent of the solar mass, while the neutrinos from ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ beta decay originate primarily in the inner five percent of the solar mass. The solar luminosity, and the flux of neutrinos from the proton-proton reaction, come mostly from an intermediate region.

This article gives a pedagogical review of recent work in which the Einstein-Hilbert gravitational action is obtained as a symmetry-breaking effect in quantum field theory. Particular emphasis is placed on the case of renormalizable field theories with dynamical scale-invariance breaking, in which the induced gravitational effective action is finite and calculable. A functional integral formulation is used throughout, and a detailed analysis is given of the role of dimensional regularization in extracting finite answers from formally quadratically divergent integrals. Expressions are derived for the induced gravitational constant and for the induced cosmological constant in quantized matter theories on a background manifold, and a strategy is outlined for computing the induced constants in the case of an $\mathrm{SU}\mathrm{}\left(n\right)\mathrm{}$ gauge theory. By use of the background field method, the formalism is extended to the case in which the metric is also quantized, yielding a derivation of the semiclassical Einstein equations as an approximation to quantum gravity, as well as general formulas for the induced (or renormalized) gravitational and cosmological constants.