88,446 research outputs found
Brane bounce-type configurations in a string-like scenario
Brane world six dimensional scenarios with string like metric has been
proposed to alleviate the problem of field localization. However, these models
have been suffering from some drawbacks related with energy conditions as well
as from difficulties to find analytical solutions. In this work, we propose a
model where a brane is made of a scalar field with bounce-type configurations
and embedded in a bulk with a string-like metric. This model produces a sound
AdS scenario where none of the important physical quantities is infinite. Among
these quantities are the components of the energy momentum tensor, which have
its positivity ensured by a suitable choice of the bounce configurations.
Another advantage of this model is that the warp factor can be obtained
analytically from the equations of motion for the scalar field, obtaining as a
result a thick brane configuration, in a six dimensional context. Moreover, the
study of the scalar field localization in these scenario is done.Comment: 15 pages, 5 figures. To appear in Physics Letters
Magnetic monopole and string excitations in a two-dimensional spin ice
We study the magnetic excitations of a square lattice spin-ice recently
produced in an artificial form, as an array of nanoscale magnets. Our analysis,
based upon the dipolar interaction between the nanomagnetic islands, correctly
reproduces the ground-state observed experimentally. In addition, we find
magnetic monopole-like excitations effectively interacting by means of the
usual Coulombic plus a linear confining potential, the latter being related to
a string-like excitation binding the monopoles pairs, what indicates that the
fractionalization of magnetic dipoles may not be so easy in two dimensions.
These findings contrast this material with the three-dimensional analogue,
where such monopoles experience only the Coulombic interaction. We discuss,
however, two entropic effects that affect the monopole interactions: firstly,
the string configurational entropy may loose the string tension and then, free
magnetic monopoles should also be found in lower dimensional spin ices;
secondly, in contrast to the string configurational entropy, an entropically
driven Coulomb force, which increases with temperature, has the opposite effect
of confining the magnetic defects.Comment: 8 pages. Accepted by Journal of Applied Physics (2009
Nonextensive Quantum H-Theorem
A proof of the quantum -theorem taking into account nonextensive effects
on the quantum entropy is shown. The positiveness of the time variation
of combined with a duality transformation implies that the nonextensive
parameter lies in the interval [0,2]. It is also shown that the equilibrium
states are described by quantum -power law extensions of the Fermi-Dirac and
Bose-Einstein distributions. Such results reduce to the standard ones in the
extensive limit, thereby showing that the nonextensive entropic framework can
be harmonized with the quantum distributions contained in the quantum
statistics theory.Comment: 5 pages, LaTe
- …