5,045 research outputs found
Varying Alpha Monopoles
We study static magnetic monopoles in the context of varying alpha theories
and show that there is a group of models for which the t'Hooft-Polyakov
solution is still valid. Nevertheless, in general static magnetic monopole
solutions in varying alpha theories depart from the classical t'Hooft-Polyakov
solution with the electromagnetic energy concentrated inside the core seeding
spatial variations of the fine structure constant. We show that Equivalence
Principle constraints impose tight limits on the allowed variations of alpha
induced by magnetic monopoles which confirms the difficulty to generate
significant large-scale spatial variation of the fine structure constant found
in previous works. This is true even in the most favorable case where magnetic
monopoles are the source for these variations.Comment: 8 pages, 10 figures; Version to be published in Phys. Rev.
Structural breaks and cointegration analysis in the EU developed markets
The strategic positioning of European economies, namely interest rate fluctuations, stock market crises, regional effects of oil prices and regional political developments make them vulnerable to real and external shocks. First signs of a sovereign debt crisis spread among financial players in the late 2009 were a result of the growing private and government debt levels worldwide. In an established crisis context, it was searched for evidence of structural breaks and cointegration between interest rates and stock market prices in the developed European markets under stress along a 13 year time-window. The results identified significant structural breaks at the end of 2010 rejecting the null hypothesis of no cointegration, and this resulted in its spread from the US to the rest of the world
Compact stars within an asy-soft quark-meson-coupling model
We investigate compact star properties within the quark meson coupling model
(QMC) with a soft symmetry energy density dependence at large densities. In
particular, the hyperon content and the mass/radius curves for the families of
stars obtained within the model are discussed. The hyperon-meson couplings are
chosen according to experimental values of the hyperon nuclear matter
potentials, and possible uncertainties are considered. It is shown that a
softer symmetry energy gives rise to stars with less hyperons, smaller radii
and larger masses. Hyperon-meson couplings may also have a strong effect on the
mass of the star.Comment: 7 pages, revtex, accepted in Phys. Rev.
The importance of the mixed phase in hybrid stars built with the Nambu-Jona-Lasinio model
We investigate the structure of hybrid stars based on two different
constructions: one is based on the Gibbs condition for phase coexistence and
considers the existence of a mixed phase (MP), and the other is based on the
Maxwell construction and no mixed phase is obtained. The hadron phase is
described by the non-linear Walecka model (NLW) and the quark phase by the
Nambu-Jona-Lasinio model (NJL). We conclude that the masses and radii obtained
are model dependent but not significantly different for both constructions.Comment: 8 pages, 7 figures, 3 table
Emergence of Clusters in Growing Networks with Aging
We study numerically a model of nonequilibrium networks where nodes and links
are added at each time step with aging of nodes and connectivity- and
age-dependent attachment of links. By varying the effects of age in the
attachment probability we find, with numerical simulations and scaling
arguments, that a giant cluster emerges at a first-order critical point and
that the problem is in the universality class of one dimensional percolation.
This transition is followed by a change in the giant cluster's topology from
tree-like to quasi-linear, as inferred from measurements of the average
shortest-path length, which scales logarithmically with system size in one
phase and linearly in the other.Comment: 8 pages, 6 figures, accepted for publication in JSTA
Fluctuations in network dynamics
Most complex networks serve as conduits for various dynamical processes,
ranging from mass transfer by chemical reactions in the cell to packet transfer
on the Internet. We collected data on the time dependent activity of five
natural and technological networks, finding that for each the coupling of the
flux fluctuations with the total flux on individual nodes obeys a unique
scaling law. We show that the observed scaling can explain the competition
between the system's internal collective dynamics and changes in the external
environment, allowing us to predict the relevant scaling exponents.Comment: 4 pages, 4 figures. Published versio
The pasta phase within density dependent hadronic models
In the present paper we investigate the onset of the pasta phase with
different parametrisations of the density dependent hadronic model and compare
the results with one of the usual parametrisation of the non-linear Walecka
model. The influence of the scalar-isovector virtual delta meson is shown. At
zero temperature two different methods are used, one based on coexistent phases
and the other on the Thomas-Fermi approximation. At finite temperature only the
coexistence phases method is used. npe matter with fixed proton fractions and
in beta-equilibrium are studied. We compare our results with restrictions
imposed on the the values of the density and pressure at the inner edge of the
crust, obtained from observations of the Vela pulsar and recent isospin
diffusion data from heavy-ion reactions, and with predictions from spinodal
calculations.Comment: 15 pages, 11 figures and 7 table
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