A lattice study of 3D compact QED at finite temperature

We study the deconfinement phase transition and monopole properties in the finite temperature 3D compact Abelian gauge model on the lattice. We predict the critical coupling as function of the lattice size in a simplified model to describe monopole binding. We demonstrate numerically that the monopoles are sensitive to the transition. In the deconfinement phase the monopoles appear in the form of a dilute gas of magnetic dipoles. In the confinement phase both monopole density and string tension differ from semiclassical estimates if monopole binding is neglected. However, the analysis of the monopole clusters shows that the relation between the string tension and the density of monopoles in charged clusters is in reasonable agreement with those predictions. We study the cluster structure of the vacuum in both phases of the model.Comment: 18 pages, 14 EPS figures, LaTeX uses epsfig.st

Monopoles, confinement and deconfinement of (2+1)D compact lattice QED in external fields

The compact Abelian model in three space--time dimensions is studied in the presence of external electromagnetic fields at finite temperatures. We show that the deconfinement phase transition is independent on the strength of the external fields. This result is in agreement with our observation that the external fields create small--size magnetic dipoles from the vacuum which do not influence the confining properties of the model. Contrary to the deconfinement phase, the internal field in the direction of the applied external field is attenuated in the confinement phase, this screening becomes stronger with decreasing temperature.Comment: 22 pages, 24 EPS figures, LaTeX uses epsfig.st

Brane world corrections to Newton's law

We discuss possible variations of the effective gravitational constant with length scale, predicted by most of alternative theories of gravity and unified models of physical interactions. After a brief general exposition, we review in more detail the predicted corrections to Newton's law of gravity in diverse brane world models. We consider various configurations in 5 dimensions (flat, de Sitter and AdS branes in Einstein and Einstein-Gauss-Bonnet theories, with and without induced gravity and possible incomplete graviton localization), 5D multi-brane systems and some models in higher dimensions. A common feature of all models considered is the existence of corrections to Newton's law at small radii comparable with the bulk characteristic length: at such radii, gravity on the brane becomes effectively multidimensional. Many models contain superlight perturbation modes, which modify gravity at large scale and may be important for astrophysics and cosmology.Comment: Brief review, 16 pages, 92 references. Some description and references adde

A Phenomenological Analysis of Gluon Mass Effects in Inclusive Radiative Decays of the J/ψ\rm{J/\psi} and $\Upsilon

The shapes of the inclusive photon spectra in the processes \Jp \to \gamma X and \Up \to \gamma X have been analysed using all available experimental data. Relativistic, higher order QCD and gluon mass corrections were taken into account in the fitted functions. Only on including the gluon mass corrections, were consistent and acceptable fits obtained. Values of $0.721^{+0.016}_{-0.068}$ GeV and $1.18^{+0.09}_{-0.29}$ GeV were found for the effective gluon masses (corresponding to Born level diagrams) for the \Jp and \Up respectively. The width ratios \Gamma(V \to {\rm hadrons})/\Gamma(V \to \gamma+ {\rm hadrons}) V=\Jp, \Up were used to determine $\alpha_s(1.5 {\rm GeV})$ and $\alpha_s(4.9 {\rm GeV})$. Values consistent with the current world average $\alpha_s$ were obtained only when gluon mass correction factors, calculated using the fitted values of the effective gluon mass, were applied. A gluon mass $\simeq 1$ GeV, as suggested with these results, is consistent with previous analytical theoretical calculations and independent phenomenological estimates, as well as with a recent, more accurate, lattice calculation of the gluon propagator in the infra-red region.Comment: 50 pages, 11 figures, 15 table

Interaction of evaporating and condensing particles in the free-molecular regime

In a previous paper it was shown that repulsive/attractive forces arise between evaporating/ condensing particles in the free-molecular regime. Here we obtain explicit expressions for these forces in the case of spherical particles with equal temperatures. The temperature of the surrounding vapor is, generally speaking, different from that of the particles. Numerical results are obtained for different values of the ratios between particle and vapor temperatures and pressures, of the particles radii and of the evaporation coefficients. In the case when the evaporation coefficient equals unity, an exact expression is obtained for the force between particles of different radii. A simple model describing coagulation processes and taking the above-mentioned forces into account is proposed. It is shown that for large values of the vapor supersaturation, the influence of these forces on the coagulation rate may be very pronounced. © 1995 American Institute of Physics