Boson Stars: Rotation, Formation, and Evolution

Boson stars are descendants of the so-calledgeons of Wheeler, except that they are built from scalarparticles instead of electromagnetic fields. If scalarfields exist in nature, such localized configurations kept together by their self-generatedgravitational field can form within Einstein's generalrelativity. In the case of complex scalar fields, anabsolutely stable branch of such non-topologicalsolitons with conserved particle number exists. Thepresent surge of interest stems from the speculativepossibility that these compact objects could provide aconsiderable fraction of the non-baryonic part of dark matter. In any case, they may serve as aconvenient laboratory for studyingnumerically rapidly rotating bodies in generalrelativity and the generation of gravitational waves.Furthermore, we mention how to detect boson stars by gravitationallensing or gravitational redshift. Finally, we explorethe evolution of boson stars within scalar-tensortheories.     

Are Axidilaton Stars Massive Compact Halo Objects?

Boson stars built from a very light Kalb–Ramond axion, the dilaton or other moduli fields of effective string models could provide a considerable fraction of the non-baryonic part of dark matter. Gravitational microlensing of 0.5 M MACHOs within the halo of galaxies may indirectly "weighing" the mass of the constituent scalar particle, resulting in 10^–10 eV/c².     

Experimental results on neutrino-electron scattering

A determination of sin² θ _w based on measurements of elastic scattering of muon-neutrinos and muon-anti-neutrinos on atomic electrons is described. These purely leptonic processes were studied using the CHARM calorimeter exposed to neutrino and antineutrino wide-band beams at the CERN super proton synchrotron. A total of 83±16 neutrino-electron and 112±21 antineutrino-electron events have been detected. From the measurement of the ratio of muon-neutrino and muon-antineutrino cross-sections a value of sin² θ _w =0.211±0.037 was obtained.     

Convergence of solutions of kinetic variational inequalities in the rate-independent quasi-static limit

This paper discusses the convergence of kinetic variational inequalities to rate-independent quasi-static variational inequalities. Mathematical formulations as well as existence and uniqueness results for kinetic and rate-independent quasi-static problems are provided. Sharp a priori estimates for the kinetic problem are derived that imply that the kinetic solutions converge to the rate-independent ones, when the size of initial perturbations and the rate of application of the forces tend to 0. An application to three-dimensional elastic-plastic systems with hardening is given.     

Global Existence for Rate-Independent Gradient Plasticity at Finite Strain

We provide a global existence result for the time-continuous elastoplasticity problem using the energetic formulation. For this, we show that the geometric nonlinearities arising from the multiplicative decomposition of the strain can be controlled via polyconvexity and a priori stress bounds in terms of the energy density. While temporal oscillations are controlled via energy dissipation, the spatial compactness is obtained via regularizing terms involving gradients of the internal variables. Dedicated to Sir John Ball on the occasion of his 60th birthday.     

Time-average measurement of velocity, density, temperature, and turbulence velocity fluctuations using Rayleigh and Mie scattering

Measurement of time-averaged velocity, density, temperature, and turbulence velocity fluctuations in sparsely seeded gas flows using a non-intrusive, point-wise technique based on Rayleigh and Mie scattering is discussed. A Fabry-Perot interferometer (FPI) is used to spectrally resolve laser light scattered by molecules and particulates in gas flows. The spectral content of the scattered light provides information about velocity, density, and temperature of the gas. A CCD camera is used to record images of the fringes formed by scattered light passing through the interferometer. Models of the spectral components are used in a least squares fitting routine to estimate the parameters from fringe images. Flow measurements are presented for subsonic and supersonic jet flows. The application range for this technique is mostly for high velocity situations (>25 m/s). Velocity, density, temperature, and turbulence velocity fluctuations were determined with accuracies within 5 m/s, 4%, 2%, and 5 m/s, respectively.     

On the Relation between Gradient Flows and the Large-Deviation Principle,with Applications to Markov Chains and Diffusion

Motivated by the occurrence in rate functions of time-dependent large-deviation principles, we study a class of non-negative functions ? that induce a flow, given by \(\mathcal{L} (\rho _{t},\dot \rho _{t})=0\) . We derive necessary and sufficient conditions for the unique existence of a generalized gradient structure for the induced flow, as well as explicit formulas for the corresponding driving entropy and dissipation functional. In particular, we show how these conditions can be given a probabilistic interpretation when ? is associated to the large deviations of a microscopic particle system. Finally, we illustrate the theory for independent Brownian particles with drift, which leads to the entropy-Wasserstein gradient structure, and for independent Markovian particles on a finite state space, which leads to a previously unknown gradient structure.     

Truncation rules for modelling discontinuities with Galerkin method in electromagnetic theory

It is well known that apparently similar discretization schemes of Maxwell's equations in Fourier series may provide very different convergence performances because of truncation. We argue that this work performed in grating theory can be applied to other electromagnetic theories relying on expansions over series different from Fourier series. This generalization is supported by an intuitive argument and by a simple numerical example with Hermite–Gauss functions.