914 research outputs found
Multi--Layer Structure in the Strongly Coupled 5D Abelian Higgs Model
We explore the phase diagram of the five-dimensional anisotropic Abelian
Higgs model by Monte Carlo simulations. In particular, we study the transition
between the confining phase and the four dimensional layered Higgs phase. We
find that, in a certain region of the lattice parameter space, this transition
can be first order and that each layer moves into the Higgs phase independently
of the others (decoupling of layers). As the Higgs couplings vary, we find,
using mean field techniques, that this transition may probably become second
order.Comment: 16 page
Phase Structure of the 5D Abelian Higgs Model with Anisotropic Couplings
We establish the phase diagram of the five-dimensional anisotropic Abelian
Higgs model by mean field techniques and Monte Carlo simulations. The
anisotropy is encoded in the gauge couplings as well as in the Higgs couplings.
In addition to the usual bulk phases (confining, Coulomb and Higgs) we find
four-dimensional ``layered'' phases (3-branes) at weak gauge coupling, where
the layers may be in either the Coulomb or the Higgs phase, while the
transverse directions are confining.Comment: LaTeX (amssymb.sty and psfig) 21 pages, 17 figure
Dynamical estimates of chaotic systems from Poincar\'e recurrences
We show that the probability distribution function that best fits the
distribution of return times between two consecutive visits of a chaotic
trajectory to finite size regions in phase space deviates from the exponential
statistics by a small power-law term, a term that represents the deterministic
manifestation of the dynamics, which can be easily experimentally detected and
theoretically estimated. We also provide simpler and faster ways to calculate
the positive Lyapunov exponents and the short-term correlation function by
either realizing observations of higher probable returns or by calculating the
eigenvalues of only one very especial unstable periodic orbit of low-period.
Finally, we discuss how our approaches can be used to treat data coming from
complex systems.Comment: subm. for publication. Accepted fpr publication in Chao
Modes of Growth in Dynamic Systems
Regardless of a system's complexity or scale, its growth can be considered to
be a spontaneous thermodynamic response to a local convergence of down-gradient
material flows. Here it is shown how growth can be constrained to a few
distinct modes that depend on the availability of material and energetic
resources. These modes include a law of diminishing returns, logistic behavior
and, if resources are expanding very rapidly, super-exponential growth. For a
case where a system has a resolved sink as well as a source, growth and decay
can be characterized in terms of a slightly modified form of the predator-prey
equations commonly employed in ecology, where the perturbation formulation of
these equations is equivalent to a damped simple harmonic oscillator. Thus, the
framework presented here suggests a common theoretical under-pinning for
emergent behaviors in the physical and life sciences. Specific examples are
described for phenomena as seemingly dissimilar as the development of rain and
the evolution of fish stocks.Comment: 16 pages, 6 figures, including appendi
Curvature corrections in DGP brane cosmology
We consider a DGP inspired brane scenario where the action on the brane is
augmented by a function of the Ricci scalar, . The cosmological
implications that such a scenario entails are examined for and shown to
be consistent with a universe expanding with power-law acceleration. It is
shown that two classes of solutions exist for the usual FRW metric and small
Hubble radii. When the Hubble radius becomes larger, we either have a
transition to a fully 5D regime or to a self-inflationary solution which
produces a late accelerated expansion such that the radius becomes a function
of .Comment: 11 pages, 2 figure
Multi-Layer Structure in the Strongly Five Dimensional Abelian Higgs Model
We explore the phase diagram of the 5--D anisotropic Abelian Higgs model by
Monte Carlo simulations. In particular, we study the transition between the
confining phase and the four dimensional layered Higgs phase. We find that, in
a certain region of the lattice parameter space, this transition can be first
order and that each layer moves into the Higgs phase independently of the
others (decoupling of layers).Comment: Lattice 2001, 3 page
Brans-Dicke DGP Brane Cosmology
We consider a five dimensional DGP-brane scenario endowed with a
non-minimally coupled scalar field within the context of Brans-Dicke theory.
This theory predicts that the mass appearing in the gravitational potential is
modified by the addition of the mass of the effective intrinsic curvature on
the brane. We also derive the effective four dimensional field equations on a
3+1 dimensional brane where the fifth dimension is assumed to have an orbifold
symmetry. Finally, we discuss the cosmological implications of this setup,
predicting an accelerated expanding universe with a value of the Brans-Dicke
parameter consistent with values resulting from the solar system
observations.Comment: 12 pages, 1 figure, to appear in JCA
Classical Stability of the Galileon
We consider the classical equations of motion for a single Galileon field
with generic parameters in the presence of non-relativistic sources. We
introduce the concept of absolute stability of a theory: if one can show that a
field at a single point---like infinity for instance---in spacetime is stable,
then stability of the field over the rest of spacetime is guaranteed for any
positive energy source configuration. The Dvali-Gabadadze-Porrati (DGP) model
is stable in this manner, and previous studies of spherically symmetric
solutions suggest that certain classes of the single field Galileon (of which
the DGP model is a subclass) may have this property as well. We find, however,
that when general solutions are considered this is not the case. In fact, when
considering generic solutions there are no choices of free parameters in the
Galileon theory that will lead to absolute stability except the DGP choice. Our
analysis indicates that the DGP model is an exceptional choice among the large
class of possible single field Galileon theories. This implies that if general
solutions (non-spherically symmetric) exist they may be unstable. Given
astrophysical motivation for the Galileon, further investigation into these
unstable solutions may prove fruitful.Comment: 23 pages, 3 figure
Towards a covariant model for cosmic self-acceleration
An explicitly covariant formulation is presented of a modified DGP scenario
proposed recently [1], to avoid the instability of the self-accelerating
branch. It is based on the introduction of a bulk scalar field with appropriate
non-minimal coupling to the bulk Einstein-Hilbert term. The method is general
and may be applied to other models as well.Comment: 10 pages, no figures; v2: version published in JHE
Inequivalence of coset constructions for spacetime symmetries
Non-linear realizations of spacetime symmetries can be obtained by a
generalization of the coset construction valid for internal ones. The physical
equivalence of different representations for spacetime symmetries is not
obvious, since their relation involves not only a redefinition of the fields
but also a field-dependent change of coordinates. A simple and relevant
spacetime symmetry is obtained by the contraction of the 4D conformal group
that leads to the Galileon group. We analyze two non-linear realizations of
this group, focusing in particular on the propagation of signals around
non-trivial backgrounds. The aperture of the lightcone is in general different
in the two representations and in particular a free (luminal) massless scalar
is mapped in a Galileon theory which admits superluminal propagation. We show
that in this theory, if we consider backgrounds that vanish at infinity, there
is no asymptotic effect: the displacement of the trajectory integrates to zero,
as can be expected since the S-matrix is trivial. Regarding local measurements,
we show that the puzzle is solved taking into account that a local coupling
with fixed sources in one theory is mapped into a non-local coupling and we
show that this effect compensates the different lightcone. Therefore the two
theories have a different notion of locality. The same applies to the different
non-linear realizations of the conformal group and we study the particular case
of a cosmologically interesting background: the Galilean Genesis scenarios
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