Some New Results on the Kinetic Ising Model in a Pure Phase

We consider a general class of Glauber dynamics reversible with respect to the standard Ising model in ^d with zero external field and inverse temperature strictly larger than the critical value _c in dimension 2 or the so called slab threshold in dimension d 3. We first prove that the inverse spectral gap in a large cube of side N with plus boundary conditions is, apart from logarithmic corrections, larger than N in d = 2 while the logarithmic Sobolev constant is instead larger than N ² in any dimension. Such a result substantially improves over all the previous existing bounds and agrees with a similar computations obtained in the framework of a one dimensional toy model based on mean curvature motion. The proof, based on a suggestion made by H. T. Yau some years ago, explicitly constructs a subtle test function which forces a large droplet of the minus phase inside the plus phase. The relevant bounds for general d 2 are then obtained via a careful use of the recent –approach to the Wulff construction. Finally we prove that in d = 2 the probability that two independent initial configurations, distributed according to the infinite volume plus phase and evolving under any coupling, agree at the origin at time t is bounded from below by a stretched exponential , again apart from logarithmic corrections. Such a result should be considered as a first step toward a rigorous proof that, as conjectured by Fisher and Huse some years ago, the equilibrium time auto-correlation of the spin at the origin decays as a stretched exponential in d = 2.     

Cosmic rays as a new instrument of seismological studies

The state of the art of the short-termearthquake prediction problemis considered. A new method for monitoring the 3D stress state in the earthquake-prone zone using high-energy muons in cosmic rays and simultaneous measurements of acoustic and seismic signals in the frequency range from 1 Hz to 1–2 kHz is proposed. To implement this method, muons should be detected simultaneously with extensive air showers in an area of several square kilometers.     

Cosmic deuterium

The knowledge of the primordial deuterium to hydrogen ratio provides one of the most reliable tests of the early Universe nucleosynthesis models and a direct estimate of the cosmic baryon density. Evaluations have been traditionally made using D/H estimations in the interstellar medium, extrapolated backwards in time with the use of galactic evolution models. Direct primordial D/H measurements have been carried out only recently in the direction of quasars. These measurements of deuterium abundances along with observations made in the solar system and in the interstellar medium are presented.New results that indicate spatial variations of the deuterium abundance in the interstellar medium at the level of 50% over scales possibly as small as 10 pc, may question our global vision of deuterium evolution until the causes for the origin of these variations are understood. With a conservative point of view, observations thus suggest that the primordial D/H value should be within the range 1. × 10⁻⁵−3. × 10⁻⁴, leading to a relatively low baryon content Universe.Since the actual evolution of deuterium from primordial nucleosynthesis to now is not known in details, more observations, hopefully to be made with the Hubble Space Telescope, FUSE the Far Ultraviolet Spectroscopic Explorer (launched in 1999). or from the ground with the largest telescopes (Keck, VLT,), should reveal the evolution of that key element, and better constrain its primordial abundance.     

Cosmic jets

We discuss time-dependent gravitational fields that “accelerate” free test particles to the speed of light resulting in cosmic double-jet configurations. It turns out that complete gravitational collapse along a spatial axis together with corresponding expansion along the other two axes leads to the accelerated motion of free test particles up and down parallel to the collapse axis such that a double-jet pattern is asymptotically formed with respect to the collapsed configuration.     

Supernova Remnants as Sources of Cosmic Rays and Nonthermal Emission

Physics of Atomic Nuclei - Cosmic ray acceleration by astrophysical shocks in supernova remnants is briefly reviewed. Results of numerical modeling taking into account magnetic field amplification...     

Cosmic Ether

A prerelativistic approach to particle dynamicsis explored in an expanding Robertson–Walkercosmology. The receding galactic background provides adistinguished frame of reference and a unique cosmictime. In this context the relativistic, purelygeometric space-time concept is criticized. Physicalspace is regarded as a permeable medium, the cosmicether, which effects the world-lines of particles andrays. We study in detail a Robertson–Walkeruniverse with linear expansion factor and negativelycurved, open three-space; we choose the permeabilitytensor of the ether in such a way that the semiclassicalapproximation is exact. Galactic red-shifts depend on therefractive index of the ether. In the local Minkowskianlimit the ether causes a time variation of mass, whichscales inversely proportional to cosmic time. In the globally geodesic rest frames of galacticobservers the ether manifests itself in an unboundedspeed of signal transfer, in bifurcations ofworld-lines, and in time inversion effects.     

Dark Matter as a Cosmic Bose-Einstein Condensate and Possible Superfluid

Dark matter arising from spontaneous symmetry breaking of a neutral scalar field coupled to gravity comprises ultra low mass bosons with a Bose-Einstein condensation temperature far above the present background temperature. Assuming galactic halos to consist of a Bose-Einstein condensate of astronomical extent, we calculate the condensate coherence length, transition temperatures, mass distribution, and orbital velocity curves, and deduce the particle mass and number density from the observed rotation curves for the Andromeda and Triangulum galaxies. We also consider the possibility of superfluid behaviour in the halos of rotating galaxies, and estimate the critical angular frequency and line density for formation of quantised vortices.     

Cosmic lacunarity

The present distribution of galaxies in space is a remnant of their formation and interaction. On a large enough scale, we may represent the galaxies as a set of points and quantify the structures in this set by its generalized dimensions [Beck and Schlogl, Thermodynamics of Chaotic Systems (Cambridge University Press, Cambridge, 1986); Paladin and Vulpiani, Phys. Rep. 156, 147 (1987)]. The results of such evaluation are often taken to be evidence of a fractal (or multifractal) distribution of galaxies. However, those results, for some scales, may also reveal the presence of singularities formed in the gravitational processes that produce structure in the galaxy distribution. To try to make some decision about this issue, we look for the more subtle galactic lacunarity. We believe that this quantity is discernible in the currently available data and that it provides important evidence on the galaxy formation process. (c) 1997 American Institute of Physics.     

Cosmic rays in the heliosphere

Summary This is a rapporteur paper for the XXIV International Cosmic-Ray Conference covering topics of anomalous cosmic rays, shock acceleration, modulation and transport theory, cosmic-ray gradients, corotating interaction regions, coronal-mass ejections, and solar neutrinos. Among the highlights of the meeting are —conclusive proof that most anomalous cosmic rays are singly charged,—undisputed detection of anomalous cosmic-ray hydrogen,—discovery of unexpectedly large anisotropies of pickup ions,—observation of pronounced solar rotational modulation of cosmic-ray fluxes to the highest heliolatitudes (∼80°) probed by the Ulysses spacecraft, and—new measurements of modulation effects sensitive to particle charge sign. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Cosmic gamma-ray bursts

All aspects of cosmic gamma-ray bursts are reviewed. First, instrumentation and experimental technique are briefly covered. Then the observable burst properties are described, and empirical classification schemes are offered. Searches for coinciding bursts at other frequencies are enumerated. The observed spatial distribution of the burst sources is given, as well as various theoretical interpretations. A section is devoted to the unusual gamma-ray burst of March 5, 1979; its features are compared to more typical events and analyzed for insights into burst origins. Theoretical models for gamma-ray bursts are considered in general, and then examined in more detail under the categories of extragalactic models, accretion onto compact objects, thermonuclear explosions, flare models, and exotic models.     

Cosmic chiral vortices

The review is devoted to cosmic chiral vortices (strings) and their possible role in the evolution of the early Universe. An exact cylindrically-symmetric solution to Einstein equations was obtained within the SU(2) sigma model for a configuration with a topological charge of the degree type. The linearized stability of the solution with respect to radial perturbations is proven by Lyapunov’s direct method. The metric found corresponds to the conical type with an angular deficiency proportional to the topological charge or the linear mass density of the vortex. The ray deflection angle close to the angular deficiency (the gravitational lens effect) was determined by direct integration of geodesic equations for the light ray orthogonal to the vortex. A gauge generalization of the model was considered involving the axially symmetric Yang-Mills field. In the approximation of the large topological charge, a solution with proper longitudinal magnetic field was obtained and the effect of a decrease in the vortex energy was found. The effect of closing the string was also considered in the approximation of the large closure radius. To this end, the toroidal moment of a closed string was calculated and an energy correction caused by the Skyrme term.     

Cosmic rays through the Higgs portal

We consider electroweak singlet dark matter with a mass comparable to the Higgs mass. The singlet is assumed to couple to standard matter through a perturbative coupling to the Higgs particle. The annihilation of a singlet in the mass range m_Sm_h is dominated by proximity to the W, Z and Higgs peaks in the annihilation cross section. We find that the continuous photon spectrum from annihilation of perturbatively coupled singlets in the galactic halo can reach a level of several per mil of the EGRET diffuse γ ray flux.     

Cosmic matter and the nonexpanding universe

The authors examine how some observations involving plasma physics in space are compatible with a recent red-shift theory. An increasingly large number of observations consistently reveal the existence of a much larger amount of intergalactic matter than presently accepted. A radio signal coming from directions between galaxies is discussed. An average density of matter in space of about 0.01 atom/cm³ is derived. It is shown that this density of matter is compatible with many reliable observations. These results lead to a nonexpanding cosmological model     

Cosmic string in the NUT-Kerr-Newman spacetime

We study the equilibrium configurations of a cosmic string described by the Nambu action in the NUT-Kerr-Newman spacetime which includes as special cases the Kerr-Newman black hole spacetime as well as the NUT spacetime which is considered as a cosmological model. In this study it is interesting to note that one can obtain parallel results for the Kerr-Newman black hole as well as the NUT spacetime.     

Cosmic rays at the highest energies

Cosmic rays at the highest energies are observed with the Pierre Auger Observatory. Recent results are discussed and the properties of high-energy cosmic rays are reviewed.