8,631 research outputs found
Trapping of Spin-0 fields on tube-like topological defects
We have considered the localization of resonant bosonic states described by a
scalar field trapped in tube-like topological defects. The tubes are
formed by radial symmetric defects in dimensions, constructed with two
scalar fields and , and embedded in the dimensional
Minkowski spacetime. The general coupling between the topological defect and
the scalar field is given by the potential .
After a convenient decomposition of the field , we find that the
amplitudes of the radial modes satisfy Schr\"odinger-like equations whose
eigenvalues are the masses of the bosonic resonances. Specifically, we have
analyzed two simple couplings: the first one is for a
fourth-order potential and, the second one is a sixth-order interaction
characterized by % . In both cases the
Schr\"odinger-like equations are numerically solved with appropriated boundary
conditions. Several resonance peaks for both models are obtained and the
numerical analysis showed that the fourth-order potential generates more
resonances than the sixth-order one.Comment: 7 pages, 10 figures, matches version published in Physics Letters
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.
First-order transition in small-world networks
The small-world transition is a first-order transition at zero density of
shortcuts, whereby the normalized shortest-path distance undergoes a
discontinuity in the thermodynamic limit. On finite systems the apparent
transition is shifted by . Equivalently a ``persistence
size'' can be defined in connection with finite-size
effects. Assuming , simple rescaling arguments imply that
. We confirm this result by extensive numerical simulation in one to
four dimensions, and argue that implies that this transition is
first-order.Comment: 4 pages, 3 figures, To appear in Europhysics Letter
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