Physics Reports

Published by Elsevier
Print ISSN: 0370-1573
The application of methods drawn from nonlinear and stochastic dynamics to the analysis of cardiovascular time series is reviewed, with particular reference to the identification of changes associated with ageing. The natural variability of the heart rate (HRV) is considered in detail, including the respiratory sinus arrhythmia (RSA) corresponding to modulation of the instantaneous cardiac frequency by the rhythm of respiration. HRV has been intensively studied using traditional spectral analyses, e.g. by Fourier transform or autoregressive methods, and, because of its complexity, has been used as a paradigm for testing several proposed new methods of complexity analysis. These methods are reviewed. The application of time-frequency methods to HRV is considered, including in particular the wavelet transform which can resolve the time-dependent spectral content of HRV. Attention is focused on the cardio-respiratory interaction by introduction of the respiratory frequency variability signal (RFV), which can be acquired simultaneously with HRV by use of a respiratory effort transducer. Current methods for the analysis of interacting oscillators are reviewed and applied to cardio-respiratory data, including those for the quantification of synchronization and direction of coupling. These reveal the effect of ageing on the cardio-respiratory interaction through changes in the mutual modulation of the instantaneous cardiac and respiratory frequencies. Analyses of blood flow signals recorded with laser Doppler flowmetry are reviewed and related to the current understanding of how endothelial-dependent oscillations evolve with age: the inner lining of the vessels (the endothelium) is shown to be of crucial importance to the emerging picture. It is concluded that analyses of the complex and nonlinear dynamics of the cardiovascular system can illuminate the mechanisms of blood circulation, and that the heart, the lungs and the vascular system function as a single entity in dynamical terms. Clear evidence is found for dynamical ageing.
Most cosmic-ray nuclei heavier than helium have suffered nuclear collisions in the interstellar gas, with transformation of nuclear composition. The isotopic and elemental composition at the sources has to be inferred from the observed composition near the Earth. The source composition permits tests of current ideas on sites of origin, nucleosynthesis in stars, evolution of stars, the mixing and composition of the interstellar medium and injection processes prior to acceleration. The effects of nuclear spallation, production of radioactive nuclides and the time dependence of their decay provide valuable information on the acceleration and propagation of cosmic rays, their nuclear transformations, and their confinement time in the Galaxy. The formation of spallation products that only decay by electron capture and are relatively long-lived permits an investigation of the nature and density fluctuations (like clouds) of the interstellar medium. Since nuclear collisions yield positrons, antiprotons, gamma rays and neutrinos, we shall discuss these topics briefly.
We review the physics basis, main features and use of general-purpose Monte Carlo event generators for the simulation of proton-proton collisions at the Large Hadron Collider. Topics included are: the generation of hard-scattering matrix elements for processes of interest, at both leading and next-to-leading QCD perturbative order; their matching to approximate treatments of higher orders based on the showering approximation; the parton and dipole shower formulations; parton distribution functions for event generators; non-perturbative aspects such as soft QCD collisions, the underlying event and diffractive processes; the string and cluster models for hadron formation; the treatment of hadron and tau decays; the inclusion of QED radiation and beyond-Standard-Model processes. We describe the principal features of the ARIADNE, Herwig++, PYTHIA 8 and SHERPA generators, together with the Rivet and Professor validation and tuning tools, and discuss the physics philosophy behind the proper use of these generators and tools. This review is aimed at phenomenologists wishing to understand better how parton-level predictions are translated into hadron-level events as well as experimentalists wanting a deeper insight into the tools available for signal and background simulation at the LHC.
A selection of results in particle physics is given from experiments with the cosmic radiation from about 1960 to December 1974. Mostly, the results are from interactions of energy greater than 105 GeV. The topics covered are: a) variation of charged particle multiplicity with energy, b) rise in the p-p cross section with energy, c) rise in the NN production cross section with energy, d) the mean pT and its distribution at energies from 105 to 108 GeV, e) the mass spectrum of ‘fireballs” and the transverse momenta of decay products in the fireball CMS, f) other emulsion chamber results including the event ‘Centauro’, g) the search and evidence for very massive, comparatively stable particles, h) interactions between 1017 and 1021 eV.
Experimental and theoretical results on the helix-coil transition of DNA are reviewed. The theoretical model of the transition is described, and the influence of heterogeneous base pair stacking, and strand dissociation on the predicted melting transition is examined. New experimental transition data on seven DNAs, 154–587 base pairs (bp) long, are reported and compared with theoretical calculations. We review and evaluate previous studies on long DNAs (≥1000 bp) as well as previous and recent results on short DNAs. The comparison of theory with equilibrium melting curves of short DNAs indicates that base pair sequence has a relatively small influence on the stacking free energy. Excellent agreement is obtained between theory and equilibrium transitions of 14 out of 15 fragments 80–587 pb. The deviation between theory and experiment for a 516 bp DNA can be attributed to the formation of stem-loop structures. This may provide the explanation for inconsistent results observed with long DNAs. The effect of single base pair changes on DNA transitions is discussed. Current views on fluctuational opening of base pairs at temperatures below the transition are described.
String theories suggest particular forms for gravity interactions in higher dimensions. We consider an interesting class of gravity theories in more than four dimensions, clarify their geometric meaning and discuss their special properties.
The nuclei 6He and 11Li which exhibit pronounced halo-structures with two loosely bound valence neutrons, are currently being explored as secondary-beam projectiles. These nuclei are Borromean, i.e. while they are bound (only one bound state) they have, considered as three-body systems, no bound states in the binary subsystems. We argue that a three-body description is the natural one for central properties of such exotic loosely bound nuclei, and give the state of the art by comparing fully blown three-body calculations for 6He (and neighboring A=6 nuclei) with a range of measured observables. We restrict this review to bound state properties, with emphasis on genuine three-body features. The bound state is the initial stage of the various reaction scenarios that now are being studied experimentally and a main objective of these studies. Currently used procedures for solving the three-body bound state problem are outlined, with emphasis on expansions on hyperspherical harmonics and also the coordinate space Faddeev approach. Although strict calculations can also be carried out for 11Li, they are inconclusive concerning the details of the structure since the available information on the binary neutron-9Li(core) channel is insufficient. Calculations for a number of plausible model interactions, including treatments of the Pauli principle, are presented. They all reproduce the binding energy and halo characteristics such as valence one-particle density and give about the same internal r.m.s. geometry for 11Li. In spite of this, the wave functions have pronounced differences in their spatial correlations. The same ambiguity is also present in other inclusive observables, such as momentum distributions. We also demonstrate that candidates for the nuclear structure can be explored within an approximate scheme COSMA. Predictions of exclusive observables are discussed, and quantities such as momentum correlations in complete measurements are found to be more sensitive to the detailed features of the nuclear structure of the bound state.
The results of an evaluation of the available photonuclear-reaction data for 12C, 14N and 16O are presented. While some reaction-yield data are given for energies up to 50 MeV, the primary emphasis is on the excitation-energy range extending from the proton separation energies up to 30 MeV. In addition to photodisintegration measurements, cross-section data derived from inverse particle-capture and electrodisintegration experiments are considered. Data are presented in graphical as well as tabular form. Included in the tables are: energy-weighted moments of the cross sections, bremsstrahlung induced reaction-yield data, radioactive-properties of reaction products, and reaction separation energies.
The evolution of a grid massive stars ranging from 12 to 40 M⊙ has been followed through all stages of nuclear burning up to the point of iron core collapse. The critical and highly uncertain rate for the reaction 12C(α, γ)16O has been varied over a range from 0.5 to 3.0 times that given by Caughlan and Fowler and two different prescriptions for semiconvection have been explored. The nucleosynthesis resulting from integrating the yields of these models over plausible initial stellar mass distributions is found to be in excellent agreement with the observed solar abundances of virtually all the intermediate mass isotopes (16 ≤ A ≤ 32) if, and only if, the rate of the 12C(α, γ)16O reaction is taken to be 1.7 ± 0.5 times that given by Caughlan and Fowler. This range is a small subset of what is allowed by current experimental measurements and can be taken as a nucleosynthetic “prediction” of the value that this rate needs to have in order to prevent 5- to 100-fold deviations from the observed relative abundances of key isotopes. These results are insensitive to the assumed slope of the initial stellar mass distribution within observational limits, and relatively insensitive to the theory of semiconvection (except for the apparent excessive production of 18O when semiconvective mixing is suppressed). Three of the stars have been followed through simulated explosions to obtain the explosive modifications to their nucleosynthesis (including the “neutrino process”), which for most isotopes is relatively small. Isotopic yields of both stable radioactive products are tabulated as are the calculated iron core masses of the presupernova stars.
The techniques of harmonic analysis of homogeneous spaces are reviewed, and applied to the theory of propagators. The spectral geometry of homogeneous and, in particular, of symmetric spaces is considered, with explicit calculations of the heat kernel and the zeta function. Several topics relevant to physical applications are discussed, including the Schwinger-DeWitt expansion, the exactness of the WKB approximation in curved spaces, the connection between free motion on symmetric spaces and quantum integrable systems, and finite-temperature quantum field theories in higher dimensions. The paper contains some new results of both mathematical and physical interest; e.g., explicit formulas for the scalar degeneracies of the Laplacian on a compact symmetric space, exact forms of the zeta function on the symmetric spaces of rank one, extension of the finite-temperature formalism to spinor fields in higher-dimensional static spacetimes, and Casimir energy calculations in even dimensions.
Anomalous scaling laws appear in a wide class of phenomena where global dilation invariance fails. In this case, the description of scaling properties requires the introduction of an infinite set of exponents.Numerical and experimental evidence indicates that this description is relevant in the theory of dynamical systems, of fully developed turbulence, in the statistical mechanics of disordered systems, and in some condensed matter problems.We describe anomalous scaling in terms of multifractal objects. They are defined by a measure whose scaling properties are characterized by a family of singularities, which are identified by a scaling exponent. Singularities corresponding to the same exponent are distributed on fractal set. The multifractal object arises as the superposition of these sets, whose fractal dimensions are related to the anomalous scaling exponents via a Legendre transformation. It is thus possible to reconstruct the probability distribution of the singularity exponents.We review the application of this formalism to the description of chaotic attractors in dissipative systems, of the energy dissipating set in fully developed turbulence, of some probability distributions in condensed matter problems. Moreover, a simple extension of the method allows us to treat from the same point of view temporal intermittency in chaotic systems and sample to sample fluctuations in disordered systems.We stress the phenomenological nature of the approach and discuss the few cases in which it was possible to reach a more fundamental understanding of anomalous scaling. We point out the need of a theory which should explain its origin and pave the way to a microscopic calculation of the probability distribution of the singularities.
Approximate resolution of linear systems of differential equations with varying coefficients is a recurrent problem, shared by a number of scientific and engineering areas, ranging from Quantum Mechanics to Control Theory. When formulated in operator or matrix form, the Magnus expansion furnishes an elegant setting to build up approximate exponential representations of the solution of the system. It provides a power series expansion for the corresponding exponent and is sometimes referred to as Time-Dependent Exponential Perturbation Theory. Every Magnus approximant corresponds in Perturbation Theory to a partial re-summation of infinite terms with the important additional property of preserving, at any order, certain symmetries of the exact solution.The goal of this review is threefold. First, to collect a number of developments scattered through half a century of scientific literature on Magnus expansion. They concern the methods for the generation of terms in the expansion, estimates of the radius of convergence of the series, generalizations and related non-perturbative expansions. Second, to provide a bridge with its implementation as generator of especial purpose numerical integration methods, a field of intense activity during the last decade. Third, to illustrate with examples the kind of results one can expect from Magnus expansion, in comparison with those from both perturbative schemes and standard numerical integrators. We buttress this issue with a revision of the wide range of physical applications found by Magnus expansion in the literature.
The theory of first order Fermi acceleration at collisionless astrophysical shock fronts is reviewed. Observations suggest that shock waves in different astrophysical environments accelerate cosmic rays efficiently. In the first order process, high energy particles diffuse through Alfvén waves that scatter them and couple them to the background plasma. These particles gain energy, on the average, every time they cross the schock front and bounce off approaching scattering centers. Calculations demonstrate that the distribution function transmitted by a plane shock is roughly a power law in momentum with slope similar to that inferred in galactic cosmic ray sources. The generation of the scattering Alfvén waves by the streaming cosmic rays is described and it is argued that the wave amplitude is probably non-linear within sufficiently strong astrophysical shocks. Hydromagnetic scattering can operate on the thermal particles as well, possibly establishing the shock structure. This suggests a model of strong collisionless shocks in which high energy particles are inevitably produced very efficiently. Observable consequences of this model, together with its limitations and some alternatives, are described. Cosmic ray origin and astrophysical shocks can no longer be considered separately.
A controversy over the possible existence of a 17 keV mass state coupled to the electron neutrino occurred during the period 1985–1993. A number of independent experiments found evidence for this state in nuclear decay spectra, while others did not. Ultimately a consensus that the 17 keV neutrino does not exist was reached. We review and evaluate the experiments that reported evidence for and against the 17 keV neutrino, and discuss the various issues of experimental systematics that contributed to the development and resolution of the controversy. We attempt to distill the lessons learned from this experience and draw some general conclusions that are relevant to future research.
Topological defects are thought to be left behind by the cosmological phase transitions which occur as the universe expands and cools. Similar processes can be studied in the phase transitions which take place in the laboratory: “Cosmological” experiments in superfluid helium and in liquid crystals were carried out within the past few years, and their results shed a new light on the dynamics of the defect-formation process. The aim of this paper is to review the key ideas behind this cosmology-condensed matter connection and to propose new experiments which could probe heretofore unaddressed aspects of the topological defects formation process.
The diversity of porous materials is noted. However, this study is particularly relevant to the use of sound absorbent materials in architectural acoustics. The theory of sound propagation within an idealised porous material consisting of a rigid matrix through which run parallel cylindrical pores normal to the surface is reviewed. Extensions to pores of arbitrary orientation and cross-section are achieved by introducing physically-measura ble microstructural constants rather than phenomenological bulk parameters that might be frequency dependent. By comparison of several theories that account for sound propagation within an elastically-framed porous material a basis is laid for an improved formulation, that takes into account both viscosity and heat conduction.The application of various propagation theories to model the reflection and transmission of sound at porous boundaries is considered. Particular attention is paid to the common assumption of local reaction and to the adequacy of modelling the porous interface as that of a quasi-homogeneous fluid. Finally the most widely used methods of measuring acoustical characteristics of porous materials at normal and oblique incidence and of obtaining their values by empirical means are surveyed.
The results from the last five years of operation of the CERN ISR are summarized, and the topics of single photons and jets, which were major results from the ISR, are discussed in more detail. The achievements of the ISR as a machine are also described very briefly.
The European Organization for nuclear research (CERN) celebrates in October 2004 its 50th anniversary. A centre of excellence for elementary particle physics research, the laboratory has contributed to the development of advanced technologies for the construction of powerful accelerators and experiments. As a follow-up of the article published by this journal in 1980, on the occasion of CERN's 25th anniversary, this contribution describes the developments of particle detectors and experimental set-ups that took place in the laboratory during the last 25 years.
I summarize some recent models and ideas for the formation of axisymmetrical structures of planetary nebulae and the three rings of SN 1987A, as follows. (a) I review the general role of binary companions, including brown dwarfs and planets. (b) I propose a mechanism for axisymmetrical mass loss on the AGB that may account for the axially symmetric structures of elliptical planetary nebulae and that operates for slowly rotating AGB stars. (c) I propose a model for the formation of the two outer rings of SN 1987A, which is based on the numerical simulation of Soker (1989), and discuss a mechanism for their displacement from the exploding star. Comment: In the proceedings of the conference Physical Processes in Astrophysical Fluids. Will be published as a special volume of Physics Reports. LATEX, 9 pages,1 figure
It is today's general wisdom that the productive use of parallel architectures depends crucially on the availability of powerful development tools and run-time environments. In this paper, we systematically discuss the fundamental software problems encountered in programming parallel architectures, in particular those with distributed resources. All these problems need to be solved, if efficient and convenient use of parallel machines is to be guaranteed. We present a five phases model of parallel application program development, which describes the required efforts in parallel programming by means of four transformation steps: problem analysis, algorithmdesign, implementation, and mapping. The major part of the paper is dedicated to the description of three research projects which focus on the last three transformation steps: SKELETON, a tool for providing improved algorithmic support for the application-oriented programmer, SPADE, an integrated development and run-time environment, and MARC, a tool for automatic mapping of parallel programs.
Supernova 1993J, a Type IIpec supernova, was discovered on March 28 in the nearby galaxy M81. The spectra displayed strong Balmer lines establishing its classification as a Type II supernova. About 26 days after explosion the Hα profile became anomalous, signaling the presence of significant amounts of helium. Additionally, the light curve displayed an anomalous double peak. We review the observations and interpretation of Supernova 1993J through the use of light curve fitting and synthetic spectra.
The status of experimental tests of general relativity to the end of 1983 is reviewed. The experimental support for the Einstein equivalence principle is summarized. If this principle is valid, gravitation must be described by a curved space-time, “metric” theory of gravity. General properties of metric theories are described and the parametrized post-Newtonian (PPN) formalism for treating the weak-field, slow-motion limit of such theories is set up. A zoo of selected metric theories of gravity is presented. Experimental tests of metric theories are then described, including the “classical” tests, tests of the strong equivalence principle, and others. The possibility of using gravitational-wave observations to test metric theories is discussed. A review is presented of the binary pulsar, in which the first evidence for gravitational radiation has been found. Finally cosmological tests of alternative theories are briefly described.
Available experimental information on the static electric quadrupole moments Q2+ of the 2+ first excited states of even-mass nuclei in the 2s1d shell is tabulated and critically reviewed, and “adopted values” are presented. The results reveal a well defined pattern for the variation of Q2+ through the shell. Predictions of Q2+ made from various nuclear models are tabulated and compared with experiment. For each nucleus the qua ty and quality of the existing data for Q2+, together with the current theoretical significance of the result, are used as criteria to determi whether new experimental work is desirable.
Observations of the high-redshift Universe with the 21 cm hyperfine line of neutral hydrogen promise to open an entirely new window onto the early phases of cosmic structure formation. Here we review the physics of the 21 cm transition, focusing on processes relevant at high redshifts, and describe the insights to be gained from such observations. These include measuring the matter power spectrum at z~50, observing the formation of the cosmic web and the first luminous sources, and mapping the reionization of the intergalactic medium. The epoch of reionization is of particular interest, because large HII regions will seed substantial fluctuations in the 21 cm background. We also discuss the experimental challenges involved in detecting this signal, with an emphasis on the Galactic and extragalactic foregrounds. These increase rapidly toward low frequencies and are especially severe for the highest redshift applications. Assuming that these difficulties can be overcome, the redshifted 21 cm line will offer unique insight into the high-redshift Universe, complementing other probes but providing the only direct, three-dimensional view of structure formation from z~200 to z~6. Comment: extended review accepted by Physics Reports, 207 pages, 44 figures (some low resolution); version with high resolution figures available at; minor changes to match published version
We review the solutions of O(N) and U(N) quantum field theories in the large N limit and as 1/N expansions, in the case of vector representations. Since invariant composite fields have small fluctuations for large N, the method relies on constructing effective field theories for composite fields after integration over the original degrees of freedom. We first solve a general scalar U(φ2) field theory for N large and discuss various non-perturbative physical issues such as critical behaviour. We show how large N results can also be obtained from variational calculations. We illustrate these ideas by showing that the large N expansion allows to relate the (φ2)2 theory and the non-linear σ-model, models which are renormalizable in different dimensions. Similarly, a relation between CP(N−1) and abelian Higgs models is exhibited. Large N techniques also allow solving self-interacting fermion models. A relation between the Gross–Neveu, a theory with a four-fermi self-interaction, and a Yukawa-type theory renormalizable in four dimensions then follows. We discuss dissipative dynamics, which is relevant to the approach to equilibrium, and which in some formulation exhibits quantum mechanics supersymmetry. This also serves as an introduction to the study of the 3D supersymmetric quantum field theory. Large N methods are useful in problems that involve a crossover between different dimensions. We thus briefly discuss finite size effects, finite temperature scalar and supersymmetric field theories. We also use large N methods to investigate the weakly interacting Bose gas. The solution of the general scalar U(φ2) field theory is then applied to other issues like tricritical behaviour and double scaling limit.
Several different lines of physical reasoning have converged on the importance of the radioactive nucleus 26Al. The sciences of meteoritics, nucleosynthesis, gamma-ray astronomy, galactic chemical evolution, solar system formation, and interstellar chemistry all place this nucleus in a central position with possible profound implications. Perhaps more importantly the study of this radioactivity can unite these diverse fields in a complicated framework which will benefit all of them. This review traces the evolution of ideas concerning 26Al in the context of these disciplines.26Al was first discussed for the possibility that its decay energy could melt meteorite parent bodies, and its daughter, 26Mg, was later found in meteorites with enhanced abundance. It was also among the first radioactivities expected to be synthesized in interestingly large quantities in nucleosynthetic events. The first definitive detection of gamma-rays from an interstellar radioactivity is that of 1.809 MeV gamma-rays from 26Al. This discovery has many implications, some of which are outlined here. The whole problem of isotopic anomalies in meteorites is greatly influenced by the specific issues surrounding excess 26Mg, whether it represents in situ decay of 26Al or memory of conditions of the ISM. The relationships among these ideas and their implications are examined.
26Al is the first cosmic radioactivity ever detected, more than ten years ago, through its characteristic 1.8 MeV gamma-ray line. Its ≈106yr lifetime, much shorter than the ≈1010yr of galactic evolution, convincingly demonstrates that nucleosynthesis is currently active in our Galaxy. Current models of nucleosynthesis are still too uncertain to allow identification of the sites of that nucleosynthetic activity, despite their continuous improvement in the past ten years. The recent results of the Compton Gamma-Ray Observatory shed, for the first time, some light on the origin of galactic 26Al, favoring massive stars as the main sources. The various measurements of 1.8 MeV emission and the theoretical models of 26Al sources are presented in this review, along with the implications of the latest results for nuclear, stellar and galactic astrophysics.
This review provides an introduction to two dimensional growth processes. Although it covers a variety of processes such as diffusion limited aggregation, it is mostly devoted to a detailed presentation of stochastic Schramm–Loewner evolutions (SLE) which are Markov processes describing interfaces in 2D critical systems. It starts with an informal discussion, using numerical simulations, of various examples of 2D growth processes and their connections with statistical mechanics. SLE is then introduced and Schramm's argument mapping conformally invariant interfaces to SLE is explained. A substantial part of the review is devoted to reveal the deep connections between statistical mechanics and processes, and more specifically to the present context, between 2D critical systems and SLE. Some of the remarkable properties of SLE are explained, together with the tools for computing with it. This review has been written with the aim of filling the gap between the mathematical and the physical literature on the subject.
The complete results of the experiments carried out with the Neutral Detector at the e+e− storage ring VEPP-2M in the energy range 2E=0.5–1.4 GeV are reviewed. The data sample corresponds to a total integrated luminosity of 19 pb−1.
We develop the quasiclassical theory for normal and superfluid liquid 3He using a systematic expansion in small parameters such as δ/EF, ϵ0−1/kF, etc., and paying particular attention to the high-energy renormalizations of the external pertubations and observables. We apply the general formalism to a number of more specific problems including the derivation of the non-linear quantum kinetic equation for normal 3He, the weak-coupling and strong-coupling free energies and static response functions for superfluid 3He, and the low-frequency and high-frequency dynamics of the superfluid phases. We also discuss extensions of the quasiclassical framework to cover strong short-ranged pertubations such as walls and ions, review recent phenomenological models for the quasiparticle scattering amplitude, and present a brief but self-contained derivation of the Keldysh perturbation theory for real-time Green's functions.
A brief review of the history of the experimental search for the neutron electric-dipole moment (EDM) is presented, followed by a discussion of the “state of the art” experimental techniques based on the storage of ultracold neutrons. Also discussed is the recent work on the construction of an improved experiment incorporating a 199Hg magnetometer within the ultracold neutron storage volume.We then review a number of well-known experimental and theoretical results and propose an entirely new experimental technique to search for the neutron EDM based on storing together, in superfluid 4He, polarized ultracold neutrons and a polarized gas of 3He atoms; this forms a unique system of two spins interacting by means of a spin-dependent mutual absorption. Such a system appears to be ideally suited for use in a neutron EDM search. Following a brief description of the method, we present an analysis of the dynamics of such a system and calculate the statistical uncertainties to be expected in an EDM search. We show that, in principle, improvement by a factor of over 1000 in the experimental limit is possible. This limit would be more than sufficient to determine whether the known CP violation leads to the observed cosmological baryon asymmetry and, in addition, would set very strict limits on the supersymmetric, multi-Higgs, and left-right-symmetric models of CP violation. We conclude with a discussion of some technical questions related to the proposed experimental technique.
The low temperature thermodynamic properties of dilute solutions of 3He in 4He are reviewed. The main emphasis is on experiments and theoretical work performed since the discovery that some 3He remains in solution even at T = 0. The experiments include measurements of the heat capacity, phase-separation, equation of state, osmotic pressure, heat of mixing, nuclear magnetic susceptibility and first- and second-sound velocities. The discussion is limited to 3He concentrations below about 15% and temperatures small enough (T ⪅0.6 K) that the contributions from thermal phonons and rotons are neglible. The dependence of the various properties on temperature, concentration and, where data exist, pressure is described and analyzed in terms of various simple theories of helium solutions. The original theory is that of Landau and Pomeranchuk in which the 3He impurities are supposed to behave as free Fermi excitations of effective mass m where m depends only on the pressure. The “Fermi entropy model”, which is useful in the analysis of thermodynamic data at finite temperature, is an empirical generalization of the Landau-Pomeranchuk theory in which the entropy is still given by the ideal Fermi gas formula, but the effective mass is allowed to depend on concentration as well as pressure. The most accurate theory (“dilute solution theory”) includes the effects of interactions between 3He excitations, and it is developed here as an expansion of the ‘osmotic energy’, U − N4μ4, in terms of the 3He quasi-particle distribution function. Various theories of the effective interaction potential and its relation to the transport properties are reviewed. The results of the experiments are compared with the predictions of the theory, based on the most recent conjectures for the interaction potential, only in the limit of T → 0 at zero pressure. The one exception is the normal mass density of the 3He component ϱn for which the theory is compared with the results of second sound experiments at all temperatures such that the effects of thermal phonons and rotons are neglible. Finally, application of the solution thermodynamics is made to the theory of dilution refrigerators.
Properties of superfluid 3He near the normal phase boundary and recent neutron scattering measurements have yielded new information about the quasiparticle interactions in 3He. For this reason these measurements have instigated the construction as well as reexamination of several phenomenological theories of the normal liquid. Among these are the paramagnon model and its generalizations and the polarization potential approximation. A review is given of these and other phenomenological models for liquid 3He and their relationship to Landau Fermi liquid theory. Quantitative comparison with experiment at different pressures for the neutron cross section, the superfluid transition temperature, the specific heat discontinuities at the superfluid phase boundary and transport properties are discussed at length. Recent advances based on kinetic theory and the dichotomy of the “localization” versus “spin fluctuation” viewpoints are summarized.
The present paper is devoted to the subject of photonuclear reactions of the type (γ, p), (γ, n), (γ, np), (γ, nn), (γ, pp) as well as nucle on capture reactions as (p, γ) at intermediate photon energies. The theoretical part of this paper reviews and extends earlier calculations of the authors up t gamma energies of Eγ ≈ 400 MeV. The paper is not intended to give a review on different theoretical approaches which have been underta ken in the past. Instead, emphasis is put on the dynamical aspects of the photonuclear reactions in order to see which elementary processes govern the reactions at different photon energies. In view of the success of the present treatment up to Eγ ≈ 120 MeV photon energy, we tempt the predictive power of the model up to photon energies of Eγ ≈ 400 MeV for the reactions in 4He and 16O.
The theory of large deviations is concerned with the exponential decay of probabilities of large fluctuations in random systems. These probabilities are important in many fields of study, including statistics, finance, and engineering, as they often yield valuable information about the large fluctuations of a random system around its most probable state or trajectory. In the context of equilibrium statistical mechanics, the theory of large deviations provides exponential-order estimates of probabilities that refine and generalize Einstein's theory of fluctuations. This review explores this and other connections between large deviation theory and statistical mechanics, in an effort to show that the mathematical language of statistical mechanics is the language of large deviation theory. The first part of the review presents the basics of large deviation theory, and works out many of its classical applications related to sums of random variables and Markov processes. The second part goes through many problems and results of statistical mechanics, and shows how these can be formulated and derived within the context of large deviation theory. The problems and results treated cover a wide range of physical systems, including equilibrium many-particle systems, noise-perturbed dynamics, nonequilibrium systems, as well as multifractals, disordered systems, and chaotic systems. This review also covers many fundamental aspects of statistical mechanics, such as the derivation of variational principles characterizing equilibrium and nonequilibrium states, the breaking of the Legendre transform for nonconcave entropies, and the characterization of nonequilibrium fluctuations through fluctuation relations. Comment: v1: 89 pages, 18 figures, pdflatex. v2: 95 pages, 20 figures, text, figures and appendices added, many references cut, close to published version
A brief review is presented of the observational and theoretical evidence for the production of iron peak nuclei in explosive nucleosynthesis, for which, under proton-rich conditions, nuclei of mass A = 56 are synthesized predominantly as 56Ni. Guided by the pioneering hydrodynamic studies of Stirling Colgate and his collaborators, it has now been firmly established that the timescale on which nuclear burning proceeds in the wake of a supernova shock wave is too short to permit any significant change (increase) in the total ratio of neutrons to protons. This guarantees dominance of the isotope 56Ni in the iron peak nuclei emerging from explosive/supernova environments, and holds important implications for the light curves of both Type I and Type II supernovae. Current models of nucleosynthesis in supernovae predict interesting and distinguishing abundance patterns that are found to be consistent with the stellar abundance determinations of halo and disk stars in our Galaxy.
This article contains a review of the physics of 5d transition metal antifluorite crystals with emphasis on the new insights that have resulted from the research of the past ten years. Section 2 contains a discussion of the lattice dynamics of these crystals. A rigid ion model is proposed and the necessary input data as obtained from various forms of spectroscopy considered. Force constants, normal mode frequencies and eigenvectors are deduced for the prototype crystal K2ReCl6. Nuclear magnetic resonance evidence for molecular reorientations is given. Section 3 presents a description of structural phase transitions in terms of the Landau theory. Evidence for several rotative type phase transitions is outlined; the soft modes are identified. A brief reference to central modes and cluster excitations is included. Data suggesting another type of structural transition, distortive in nature, are introduced. Section 4 provides an overview of our knowledge of the transferred hyperfine interaction and of the magnetic structure in the antiferromagnetic phase. In section 5 three topics considered peripheral to the main body of the article are mentioned briefly. These are the nature of the chemical bond, the study of mixed crystals and protonic conduction.
Recent progress of experimental investigations that show explicitly spin-dependent effects is reported for inelastic electron-atom scattering. In particular the combined effect of exchange scattering and target coupling is discussed in more detail. The experimental investigation of this ‘target-coupling effect’ is a powerful method to study the influence of exchange scattering directly. The experiments that are reviewed are basically target and electron spin-polarization measurements and the determination of the angular momentum state of the atom after scattering.
The effective restoration of $SU(2)_L \times SU(2)_R$ and $U(1)_A$ chiral symmetries of QCD in excited hadrons is reviewed. While the low-lying hadron spectrum is mostly shaped by the spontaneous breaking of chiral symmetry, in the high-lying hadrons the role of the quark condensate of the vacuum becomes negligible and the chiral symmetry is effectively restored. This implies that the mass generation mechanisms in the low- and high-lying hadrons are essentially different. The fundamental origin of this phenomenon is a suppression of quark quantum loop effects in high-lying hadrons relative to the classical contributions that preserve both chiral and $U(1)_A$ symmetries. Microscopically the chiral symmetry breaking is induced by the dynamical Lorentz-scalar mass of quarks due to their coupling with the quark condensate of the vacuum. This mass is strongly momentum-dependent, however, and vanishes in the high-lying hadrons where the typical momentum of valence quarks is large. This physics is illustrated within the solvable chirally-symmetric and confining model. Effective Lagrangians for the approximate chiral multiplets at the hadron level are constructed which can be used as phenomenological effective field theories in the effective chiral restoration regime. Different ramifications and implications of the effective chiral restoration for the string description of excited hadrons, the decoupling of excited hadrons from the Goldstone bosons, the glueball - quark-antiquark mixing and the OZI rule violations are discussed.
To determine the needs, priorities and accuracies of the atomic and molecular physics data required for plasma modelling the rôle of these data in computer simulations of magnetically confined plasmas is reviewed. The models approximate atomic and molecular reactions in many different ways. Multi-dimensional calculations concerned with the equilibrium and stability of a plasma-magnetic field configuration assume the plasma to consist of fully ionised hydrogen ions and electrons in the magnetohydrodynamic approximation: the effect of atomic and molecular reactions is minimal. Zero (spatial) dimensional calculations of the break-down phase of gas discharges assume the gas to consist of atomic and molecular hydrogen, electrons and impurity ions such as oxygen, carbon, iron, tungsten and molybdenum: the effect of plasma motion is minimal. Between these extremes are classes of computations such as the one (spatial) dimension transport calculations which attempt to establish a realistic balance between the behaviour of ions, atoms and molecules in an established discharge. The limitations and inadequacies of present data and models for atomic and molecular processes are illustrated by several specific calculations. The results of these calculations permit identification of the ar eas where improved models and data for the atomic and molecular reactions are required.
In high-temperature low-density plasmas radiation cooling by impurity atoms can be an important energy loss mechanism, since the radiation is not reabsorbed. In a brief historical survey it is shown that the problem is not new but was discussed since the first beginning of controlled thermo-nuclear fusion research. It is then shown how radiation losses enter into the general power balance equation of a plasma containing impurities. The equations for the different types of radiation losses are given as a function of the atomic quantities. In a special section simplications due to the corona model assumption are discussed. It follows a detailed survey of the results obtained by several authors for the ionization balance and power losses of impurity elements observed in present high-temperature plasma machines used in CTR, especially in Tokamaks. In the conclusion a survey is given of the atomic data which experimentalists and theorists need for current research on impurities in fusion-like plasmas.
Dynamical properties of atoms on surfaces depend sensitively on their bonding environment and thus provide valuable insight into the local geometry and chemical binding at the boundary of a solid. Density-functional theory provides a unified approach to the calculation of structural and dynamical properties from first principles. Its high accuracy and predictive power for lattice dynamical properties of semiconductor surfaces has been demonstrated in a previous article by Fritsch and Schröder (Phys. Rep. 309 (1999) 209). In this report, we review the state-of-the-art of these ab initio approaches to surface dynamical properties of metal surfaces. We give a brief introduction to the conceptual framework with focus on recent advances in computational procedures for the ab initio linear-response approach, which have been a prerequisite for an efficient treatment of surface dynamics of noble and transition metals. The discussed applications to clean and adsorbate-covered surfaces demonstrate the high accuracy and reliability of this approach in predicting detailed microscopic properties of the phonon dynamics for a wide range of metallic surfaces.
A method for theoretical ab initio treatment of the Renner-Teller effect in tetra-atomic molecules is described. It is based on the model developed in 1972 by Petelin and Kiselev, but instead perturbationally, as in the original work, the vibronic problem is solved by a variational approach. The reliability of the approximations on which the model is based is discussed in detail and checked by the explicit ab initio computations carried out at various levels of sophistication. The model is extended to take into account the interplay between the vibronic, spin-orbit and magnetic hyperfine couplings. The results of ab initio investigations of the structure of spectra involving the ground states, X2Πu of C2H+2 and B2H+2 are reviewed.
Some problems arising from the use of the Coulomb gauge in SU(2) Yang-Mills theory are discussed. It is shown that: i) the transversality condition does not fix the gauge uniquely (Gribov ambiguity); ii) there exist physical configurations that cannot be described by a continuous Aμ in the Coulomb gauge.
The theory of Abelian and non-Abelian magnetic monopoles is reviewed with special focus on the exact integrability properties of such systems.The limit of vanishing Higgs potential (Prasad-Sommerfield limit) is analyzed in detail. At the classical level, the construction of all static multimonopole solutions is presented, with emphasis on the explicit axially symmetric states. At the semiclassical level, the problems of small fluctuations, bosonic and fermionic zero modes and the construction of static propagators are discussed.Finally we consider the possibility of embedding monopoles in supersymmetric theories in order to obtain models with stronger convergence properties and possibly full quantum mechanical integrability.
The purpose of this paper is to review the recent progress in understanding quark confinement. The emphasis of this review is placed on how to obtain a manifestly gauge-independent picture for quark confinement supporting the dual superconductivity in the Yang-Mills theory, which should be compared with the Abelian projection proposed by 't Hooft. The basic tools are reformulations of the Yang-Mills theory based on change of variables extending the decomposition of the $SU(N)$ Yang-Mills field due to Cho, Duan-Ge and Faddeev-Niemi, together with the combined use of extended versions of the Diakonov-Petrov version of the non-Abelian Stokes theorem for the $SU(N)$ Wilson loop operator. Moreover, we give the lattice gauge theoretical versions of the new reformulation of the Yang-Mills theory which enables us to perform the numerical simulations on the lattice. In fact, we present some numerical evidences for supporting the (non-Abelian) dual superconductivity for quark confinement. The numerical simulations include the derivation of the linear potential for static interquark potential, i.e., non-vanishing string tension, in which the Abelian dominance and magnetic monopole dominance are established, confirmation of the dual Meissner effect by measuring the chromoelectric flux tube between quark-antiquark pair, the induced magnetic-monopole current, and the type of dual superconductivity, etc. In addition, we give a direct connection between the topological configuration of the Yang-Mills field such as instantons/merons and the magnetic monopole.
The vortex solutions of various classical planar field theories with (Abelian) Chern–Simons term are reviewed. Relativistic vortices, put forward by Paul and Khare, arise when the Abelian Higgs model is augmented with the Chern–Simons term. Adding a suitable sixth-order potential and turning off the Maxwell term provides us with pure Chern–Simons theory, with both topological and non-topological self-dual vortices, as found by Hong–Kim–Pac, and by Jackiw–Lee–Weinberg. The non-relativistic limit of the latter leads to non-topological Jackiw–Pi vortices with a pure fourth-order potential. Explicit solutions are found by solving the Liouville equation.The scalar matter field can be replaced by spinors, leading to fermionic vortices.Alternatively, topological vortices in external field are constructed in the phenomenological model proposed by Zhang–Hansson–Kivelson. Non-relativistic Maxwell–Chern–Simons vortices are also studied.The Schrödinger symmetry of Jackiw–Pi vortices, as well as the construction of some time-dependent vortices, can be explained by the conformal properties of non-relativistic space–time, derived in a Kaluza–Klein-type framework.
We present a review of gravitating particle-like and black hole solutions with non-Abelian gauge fields. The emphasis is given to the description of the structure of the solutions and to the connection with the results of flat space soliton physics. We describe the Bartnik–McKinnon solitons and the non-Abelian black holes arising in the Einstein–Yang–Mills theory, and consider their various generalizations. These include axially symmetric and slowly rotating configurations, solutions with higher gauge groups, Λ-term, dilaton, and higher curvature corrections. The stability issue is discussed as well. We also describe the gravitating generalizations for flat space monopoles, sphalerons, and Skyrmions.
Above-Threshold Ionization (ATI) is the name given to the absorption by an atomic electron of more photons than are required for ionization. ATI was discovered in 1979 and is now expected to be a universal phenomenon observable in all atomic species. The effect occurs readily in light pulses short enough to eliminate the influence of collisions, at intensities above 1 TW/cm2.
This paper reviews the experimental and phenomenological aspects of electron-positron annihilation into hadrons at center-of-mass energies above 2 GeV. The behavior of the total cross section for hadron production as a function of energy is described; and the important parameter R - the ratio of this cross section to the muon-pair production cross section - is discussed. Data on charged particle multiplicities, particle production ratios, and single particle inclusive distributions is also summarized. The paper than summarizes our knowledge of the newly discovered ψ particles; and examines the various theories as to their nature and their relation to conventional hadronic physics.
Top-cited authors
Stefano Boccaletti
  • Italian National Research Council
Yamir Moreno
  • University of Zaragoza
Santo Fortunato
  • Indiana University Bloomington
Vito Latora
  • Queen Mary, University of London
Juergen Kurths
  • Potsdam Institute for Climate Impact Research