We review the present status of QCD corrections to weak decays beyond the leading-logarithmic approximation, including particle-antiparticle mixing and rare and CP-violating decays. After presenting the basic formalism for these calculations we discuss in detail the effective Hamiltonians of all decays for which the next-to-leading-order corrections are known. Subsequently, we present the phenomenological implications of these calculations. The values of various parameters are updated, in particular the mass of the newly discovered top quark. One of the central issues in this review are the theoretical uncertainties related to renormalization-scale ambiguities, which are substantially reduced by including next-to-leading-order corrections. The impact of this theoretical improvement on the determination of the Cabibbo-Kobayashi-Maskawa matrix is then illustrated.
The authors review the relation between the inflationary potential and the spectra of density waves (scalar perturbations) and gravitational waves (tensor perturbations) produced, with particular emphasis on the possibility of reconstructing the inflaton potential from observations. The spectra provide a potentially powerful test of the inflationary hypothesis; they are not independent but instead are linked by consistency relations reflecting their origin from a single inflationary potential. To lowest order in a perturbation expansion there is a single, now familiar, relation between the tensor spectral index and the relative amplitude of the spectra. The authors demonstrate that there is an infinite hierarchy of such consistency equations, though observational difficulties suggest only the first is ever likely to be useful. They also note that since observations are expected to yield much better information on the scalars than on the tensors, it is likely to be the next-order version of this consistency equation that will be appropriate, not the lowest-order one. If inflation passes the consistency test, one can then confidently use the remaining observational information to constrain the inflationary potential, and the authors survey the general perturbative scheme for carrying out this procedure. Explicit expressions valid to next-lowest order in the expansion are presented. The prospects for future observations' reaching the quality required are then briefly assessed and simulated data sets motivated by this outlook are considered.
Contrary to naive cosmological expectations, all evidence suggests that the universe contains an abundance of matter over antimatter. This article reviews the currently popular scenario in which testable physics, present in the standard model of electroweak interactions and its modest extensions, is responsible for this fundamental cosmological datum. A pedagogical explanation of the motivations and physics behind electroweak baryogenesis is provided, and analytical approaches, numerical studies, up to date developments, and open questions in the field are also discussed. [S0034-6861(99)00105-1].
Helium and heavy-element diffusion are both included in precise calculations of solar models. In addition, improvements in the input data for solar interior models are described for nuclear reaction rates, the solar luminosity, the solar age, heavy-element abundances, radiative opacities, helium and metal diffusion rates, and neutrino interaction cross sections. The effects on the neutrino fluxes of each change in the input physics are evaluated separately by constructing a series of solar models with one additional improvement added at each stage. The effective 1 sigma uncertainties in the individual input quantities are estimated and used to evaluate the uncertainties in the calculated neutrino fluxes and the calculated event rates for solar neutrino experiments. The calculated neutrino event rates, including all of the improvements, are 9.3(-1.4)(+1.2) SNU for the Cl-37 experiment and 137(-7)(+8) SNU for the Ga-71 experiments. The calculated flux of Be-7 neutrinos is 5.1 1.00(-0.07)(+0.06)) X 10(9) cm(-2) s(-1) and the flux of B-8 neutrinos is 6.6(1.00(-0.17)(+0.14) X 10(6) cm(-2) s(-1). The primordial helium abundance found for this model is Y=0.278. The present-day surface abundance of the model is Y-s=0.247, in agreement with the helioseismological measurement of Y-s=0.242+/-0.003 determined by Hernandez and Christensen-Dalsgaard (1994). The computed depth of the convective zone is R=0.712R(circle dot) , in agreement with the observed value determined from p-mode oscillation data of R=0.713+/-0.003R(circle dot) found by Christensen-Dalsgaard et al. (1991). Although the present results increase the predicted event rate in the four operating solar neutrino experiments by almost 1 sigma (theoretical uncertainty), they only slightly increase the difficulty of explaining the existing experiments with standard physics (i.e., by assuming that nothing happens to the neutrinos after they are created in the center of the sun). For an extreme model in which all diffusion (helium and heavy-element diffusion) is neglected, the event rates are 7.0(-1.0)(+0.9) SNU for the Cl-37 experiment and 126(-6)(+6) SNU for the Ga-71 experiments, while the Be-7 and B-8 neutrino fluxes are, respectively, 4.5(1.00(-0.07)(+0.06)) X 10(9) cm(-2) s(-1) and 4.9(1.00(-0.17)(+0.14)) X 10(6) cm(-2) S-1. For the no-diffusion model, the computed value of the depth of the convective zone is R = 0.726R(circle dot), which disagrees with the observed helioseismological value. The calculated surface abundance of helium, Y-s=0.268, is also in disagreement with the p-mode measurement. The authors conclude that helioseismology provides strong evidence for element diffusion and therefore for the somewhat larger solar neutrino event rates calculated in this paper.
Although thermodynamic fluctuation theory originated from statistical mechanics, it may be put on a completely thermodynamic basis, in no essential need of any microscopic foundation. This review views the theory from the macroscopic perspective, emphasizing, in particular, notions of covariance and consistency, expressed naturally using the language of Riemannian geometry. Coupled with these concepts is an extension of the basic structure of thermodynamic fluctuation theory beyond the classical one of a subsystem in contact with an infinite uniform reservoir. Used here is a hierarchy of concentric subsystems, each of which samples only the thermodynamic state of the subsystem immediately larger than it. The result is a covariant thermodynamic fluctuation theory which is plausible beyond the standard second-order entropy expansion. It includes the conservation laws and is mathematically consistent when applied to fluctuations inside subsystems. Tests on known models show improvements. Perhaps most significantly, the covariant theory offers a qualitatively new tool for the study of fluctuation phenomena: the Riemannian thermodynamic curvature. The thermodynamic curvature gives, for any given thermodynamic state, a lower bound for the length scale where the classical thermodynamic fluctuation theory based on a uniform environment could conceivably hold. Straightforward computation near the critical point reveals that the curvature equals the correlation volume, a physically appealing finding. The combination of the interpretation of curvature with a well-known proportionality between the free energy and the inverse of the correlation volume yields a purely thermodynamic theory of the critical point. The scaled equation of state follows from the values of the critical exponents. The thermodynamic Riemannian metric may be put into the broader context of information theory.
The authors review the experimental measurements and theoretical descriptions of leptonic and semileptonic decays of particles containing a single heavy quark, either charm or bottom. Measurements of bottom semileptonic decays are used to determine the magnitudes of two fundamental parameters of the standard model, the Cabibbo-Kobayashi-Maskawa matrix elements V-cb and V-ub. These parameters are connected with the physics of quark flavor and mass, and they have important implications for the breakdown of CP symmetry. To extract precise values of /V-cb/ and /V-ub/ from measurements, however, requires a good understanding of the decay dynamics. Measurements of both charm and bottom decay distributions provide information on the interactions governing these processes. The underlying weak transition in each case is relatively simple, but the strong interactions that bind the quarks into hadrons introduce complications. The authors also discuss new theoretical approaches, especially heavy-quark effective theory and lattice QCD, which are providing insights and predictions now being rested by experiment. An international effort at many laboratories will rapidly advance knowledge of this area of physics during the next decade.
The development of different analytical and approximate numerical methods for calculations of shock-wave propagation in the inhomogeneous interstellar medium is reviewed. The models of ultracompact H II regions, nonspherical supernova remnants, bubbles produced by stellar winds of hot stars, and expanding supershells are discussed on the basis of these calculations.
Irreversible fractal-growth models like diffusion-limited aggregation (DLA) and the dielectric breakdown model (DBM) have confronted us with theoretical problems of a new type for which standard concepts like field theory and renormalization group do not seem to be suitable. The fixed-scale transformation (FST) is a theoretical scheme of a novel type that can deal with such problems in a reasonably systematic way. The main idea is to focus on the irreversible dynamics at a given scale and to compute accurately the nearest-neighbor correlations at this scale by suitable lattice path integrals. The next basic step is to identify the scale-invariant dynamics that refers to coarse-grained variables of arbitrary scale. The use of scale-invariant growth rules allows us to generalize these correlations to coarse-grained cells of any size and therefore to compute the fractal dimension. The basic point is to split the long-time limit (t>infinity) for the dynamical process at a given scale that produces the asymptotically frozen structure, from the large-scale limit (r>infinity) which defines the scale-invariant dynamics. In addition, by working at a fixed scale with respect to dynamical evolution, it is possible to include the fluctuations of boundary conditions and to reach;a remarkable level of accuracy for a real-space method. This new framework is able to explain the self-organized critical nature and the origin of fractal structures in irreversible-fractal-growth models, it also provides a rather systematic procedure for the analytical calculation of the fractal dimension and other critical exponents. The FST method can be naturally extended to a variety of equilibrium and nonequilibrium models that generate fractal structures.
The scanning acoustic microscope is a powerful new tool for the study of the physical properties of materials and has been successfully used for imaging interior structures and for nondestructive evaluation in materials science and biology. Its principles of operation, resolution, penetration ability, and contrast mechanisms are simply described in this paper. Recent progress in the application of acoustic microscopy to material characterization in solid materials is summarized. The experimental elastic microanalysis of bulk materials is carried out by measuring V(z), which includes examining the reflectance function of solid material, measuring the phase velocity and attenuation of leaky surface acoustic waves at the liquid-specimen boundary, and determining the elastic constants of the material. The layer thickness and mechanical properties of layered solids are studied by examining the dispersion properties of surface acoustic waves. A knowledge of the propagation properties of acoustic waves on the surface of materials is essential for understanding the contrast mechanisms and quantitative measurements in acoustic microscopy; these propagation properties are thus also briefly described in this paper. Finally, further developments of the scanning acoustic microscope aimed at improving its performance for quantitative evaluation are presented. These could expand the scope of the acoustic microscope as a diagnostic tool in many areas of science and technology.
We describe an experimental technique that allows for the direct determination of the motion (i.e., the momentum) of electrons in atoms, molecules, and solids. This (e,2e) technique centers on a fast electron's ejecting a second electron from a target. Precise spectroscopy of both electrons' final energies and momenta provides very significant information on the second electron's initial state. Decades of past (e,2e) studies on single-molecule states have now progressed into studies of condensed matter. The interpretation of these experiments is mediated in this colloquium by analysis of Intermediate models in the form of chainlike molecules.
A precise form of the quantum-mechanical time-energy uncertainty relation is derived. For any given initial state (density operator), time-dependent Hamiltonian, and subspace of reference states, it gives upper and lower bounds for the probability of finding the system in a state in that. subspace at a later or earlier time. The bounds involve only the initial data, the energy uncertainty in the initial state, and the energy uncertainty in the reference subspace. They describe how fast the state enters or leaves the reference subspace. They are exact if, but not only if, the initial state or the projection onto the reference subspace commutes with the Hamiltonian. The basic tool used in the proof is a simple inequality for expectation values of commutators, which generalizes the usual uncertainty relation. By introducing suitable comparison dynamics (trial propagators), the bounds can be made arbitrarily tight. They represent a time-dependent variational principle, in terms of trial propagators, which provides explicit error estimates and reproduces the exact time evolution when one varies over ail trial propagators. As illustrations, we derive accurate lower bounds on the escape time of a particle out of a potential well modeling a quantum dot, and the total time before which a He+ ion moving in a uniform magnetic field loses its electron.