49,107 research outputs found
Computability of the causal boundary by using isocausality
Recently, a new viewpoint on the classical c-boundary in Mathematical
Relativity has been developed, the relations of this boundary with the
conformal one and other classical boundaries have been analyzed, and its
computation in some classes of spacetimes, as the standard stationary ones, has
been carried out.
In the present paper, we consider the notion of isocausality given by
Garc\'ia-Parrado and Senovilla, and introduce a framework to carry out
isocausal comparisons with standard stationary spacetimes. As a consequence,
the qualitative behavior of the c-boundary (at the three levels: point set,
chronology and topology) of a wide class of spacetimes, is obtained.Comment: 44 pages, 5 Figures, latex. Version with minor changes and the
inclusion of Figure
Classical singularities and Semi-Poisson statistics in quantum chaos and disordered systems
We investigate a 1D disordered Hamiltonian with a non analytical step-like
dispersion relation whose level statistics is exactly described by Semi-Poisson
statistics(SP). It is shown that this result is robust, namely, does not depend
neither on the microscopic details of the potential nor on a magnetic flux but
only on the type of non-analyticity. We also argue that a deterministic kicked
rotator with a non-analytical step-like potential has the same spectral
properties. Semi-Poisson statistics (SP), typical of pseudo-integrable
billiards, has been frequently claimed to describe critical statistics, namely,
the level statistics of a disordered system at the Anderson transition (AT).
However we provide convincing evidence they are indeed different: each of them
has its origin in a different type of classical singularities.Comment: typos corrected, 4 pages, 3 figure
Isocausal spacetimes may have different causal boundaries
We construct an example which shows that two isocausal spacetimes, in the
sense introduced by Garc\'ia-Parrado and Senovilla, may have c-boundaries which
are not equal (more precisely, not equivalent, as no bijection between the
completions can preserve all the binary relations induced by causality). This
example also suggests that isocausality can be useful for the understanding and
computation of the c-boundary.Comment: Minor modifications, including the title, which matches now with the
published version. 12 pages, 3 figure
Nonlinear response of superparamagnets with finite damping: an analytical approach
The strongly damping-dependent nonlinear dynamical response of classical
superparamagnets is investigated by means of an analytical approach. Using
rigorous balance equations for the spin occupation numbers a simple approximate
expression is derived for the nonlinear susceptibility. The results are in good
agreement with those obtained from the exact (continued-fraction) solution of
the Fokker-Planck equation. The formula obtained could be of assistance in the
modelling of the experimental data and the determination of the damping
coefficient in superparamagnets.Comment: 7 PR pages, 2 figure
Exotic dynamically generated baryons with C1
We follow a model based on the SU(8) symmetry for the interaction of mesons
with baryons. The model treats on an equal footing the pseudo-scalars and the
vector mesons, as required by heavy quark symmetry. The T-matrix calculated
within an unitary scheme in coupled channels has poles which are interpreted as
baryonic resonances.Comment: 5 pages. Proceedings for Chiral10 workshop, Valencia, June 21-24 201
Pair Creation of Dilaton Black Holes in Extended Inflation
Dilatonic Charged Nariai instantons mediate the nucleation of black hole
pairs during extended chaotic inflation. Depending on the dilaton and inflaton
fields, the black holes are described by one of two approximations in the
Lorentzian regime. For each case we find Euclidean solutions that satisfy the
no boundary proposal. The complex initial values of the dilaton and inflaton
are determined, and the pair creation rate is calculated from the Euclidean
action. Similar to standard inflation, black holes are abundantly produced near
the Planck boundary, but highly suppressed later on. An unusual feature we find
is that the earlier in inflation that the dilatonic black holes are created,
the more highly charged they can be.Comment: 23 pages, LaTeX, 6 figures; submitted to Phys. Rev.
Structural instability of vortices in Bose-Einstein condensates
In this paper we study a gaseous Bose-Einstein condensate (BEC) and show
that: (i) A minimum value of the interaction is needed for the existence of
stable persistent currents. (ii) Vorticity is not a fundamental invariant of
the system, as there exists a conservative mechanism which can destroy a vortex
and change its sign. (iii) This mechanism is suppressed by strong interactions.Comment: 4 pages with 3 figures. Submitted to Phys. Rev. Let
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