703 research outputs found
Multi-particle quantum chaos in tilted optical lattices
We show that, in the parameter regime of state of the art experiments on Bose
Einstein Condensates loaded into optical lattices, the energy spectrum of the
1D Bose-Hubbard model amended by a static field exhibits unambiguous signatures
of quantum chaos. In the dynamics, this leads to the irreversible decay of
Bloch oscillations.Comment: 3 pages, 3 figur
Genericity of blackhole formation in the gravitational collapse of homogeneous self-interacting scalar fields
The gravitational collapse of a wide class of self-interacting homogeneous
scalar fields models is analyzed. The class is characterized by certain general
conditions on the scalar field potential, which, in particular, include both
asymptotically polynomial and exponential behaviors. Within this class, we show
that the generic evolution is always divergent in a finite time, and then make
use of this result to construct radiating star models of the Vaidya type. It
turns out that blackholes are generically formed in such models.Comment: 18 pages, 4 figure
Quantum Chaos in the Bose-Hubbard model
We present a numerical study of the spectral properties of the 1D
Bose-Hubbard model. Unlike the 1D Hubbard model for fermions, this system is
found to be non-integrable, and exhibits Wigner-Dyson spectral statistics under
suitable conditions.Comment: 4 pages, 4 figure
A Morse-theoretical analysis of gravitational lensing by a Kerr-Newman black hole
Consider, in the domain of outer communication of a Kerr-Newman black hole, a
point (observation event) and a timelike curve (worldline of light source).
Assume that the worldline of the source (i) has no past end-point, (ii) does
not intersect the caustic of the past light-cone of the observation event, and
(iii) goes neither to the horizon nor to infinity in the past. We prove that
then for infinitely many positive integers k there is a past-pointing lightlike
geodesic of (Morse) index k from the observation event to the worldline of the
source, hence an observer at the observation event sees infinitely many images
of the source. Moreover, we demonstrate that all lightlike geodesics from an
event to a timelike curve in the domain of outer communication are confined to
a certain spherical shell. Our characterization of this spherical shell shows
that in the Kerr-Newman spacetime the occurrence of infinitely many images is
intimately related to the occurrence of centrifugal-plus-Coriolis force
reversal.Comment: 14 pages, 2 figures; REVTEX; submitted to J. Math. Phy
Gravitational lensing in spherically symmetric static spacetimes with centrifugal force reversal
In Schwarzschild spacetime the value of the radius coordinate is
characterized by three different properties: (a) there is a ``light sphere'',
(b) there is ``centrifugal force reversal'', (c) it is the upper limiting
radius for a non-transparent Schwarschild source to act as a gravitational lens
that produces infinitely many images. In this paper we prove a theorem to the
effect that these three properties are intimately related in {\em any}
spherically symmetric static spacetime. We illustrate the general results with
some examples including black-hole spacetimes and Morris-Thorne wormholes.Comment: 18 pages, 3 eps-figure
Dormant Mycobacterium tuberculosis fails to block phagosome maturation and shows unexpected capacity to stimulate specific human T lymphocytes
Dormancy is defined as a stable but reversible nonreplicating state of Mycobacterium tuberculosis. It is currently thought that dormant M. tuberculosis (D-Mtb) is responsible for latent tuberculosis (TB) infection. Recently, D-Mtb was also shown in sputa of patients with active TB, but the capacity of D-Mtb to stimulate specific immune responses was not investigated. We observed that purified protein derivative-specific human CD4(+) T lymphocytes recognize mycobacterial Ags more efficiently when macrophages are infected with D-Mtb instead of replicating M. tuberculosis (R-Mtb). The different Ag recognition occurs even when the two forms of mycobacteria equally infect and stimulate macrophages, which secrete the same cytokine pattern and express MHC class I and II molecules at the same levels. However, D-Mtb but not R-Mtb colocalizes with mature phagolysosome marker LAMP-1 and with vacuolar proton ATPase in macrophages. D-Mtb, unlike R-Mtb, is unable to interfere with phagosome pH and does not inhibit the proteolytic efficiency of macrophages. We show that D-Mtb downmodulates the gene Rv3875 encoding for ESAT-6, which is required by R-Mtb to block phagosome maturation together with Rv3310 gene product SapM, previously shown to be downregulated in D-Mtb. Thus, our results indicate that D-Mtb cannot escape MHC class II Ag-processing pathway because it lacks the expression of genes required to block the phagosome maturation. Data suggest that switching to dormancy not only represents a mechanism of survival in latent TB infection, but also a M. tuberculosis strategy to modulate the immune response in different stages of TB
Point perturbations of circle billiards
The spectral statistics of the circular billiard with a point-scatterer is
investigated. In the semiclassical limit, the spectrum is demonstrated to be
composed of two uncorrelated level sequences. The first corresponds to states
for which the scatterer is located in the classically forbidden region and its
energy levels are not affected by the scatterer in the semiclassical limit
while the second sequence contains the levels which are affected by the
point-scatterer. The nearest neighbor spacing distribution which results from
the superposition of these sequences is calculated analytically within some
approximation and good agreement with the distribution that was computed
numerically is found.Comment: 9 pages, 2 figure
Explicitly solvable cases of one-dimensional quantum chaos
We identify a set of quantum graphs with unique and precisely defined
spectral properties called {\it regular quantum graphs}. Although chaotic in
their classical limit with positive topological entropy, regular quantum graphs
are explicitly solvable. The proof is constructive: we present exact periodic
orbit expansions for individual energy levels, thus obtaining an analytical
solution for the spectrum of regular quantum graphs that is complete, explicit
and exact
The Elliptic Billiard: Subtleties of Separability
Some of the subtleties of the integrability of the elliptic quantum billiard
are discussed. A well known classical constant of the motion has in the quantum
case an ill-defined commutator with the Hamiltonian. It is shown how this
problem can be solved. A geometric picture is given revealing why levels of a
separable system cross. It is shown that the repulsions found by Ayant and
Arvieu are computational effects and that the method used by Traiber et al. is
related to the present picture which explains the crossings they find. An
asymptotic formula for the energy-levels is derived and it is found that the
statistical quantities of the spectrum P(s) and \Delta(L) have the form
expected for an integrable system.Comment: 10 pages, LaTeX, 3 Figures (postscript). Submitted to European
Journal of Physic
New mathematical framework for spherical gravitational collapse
A theorem, giving necessary and sufficient condition for naked singularity
formation in spherically symmetric non static spacetimes under hypotheses of
physical acceptability, is formulated and proved. The theorem relates existence
of singular null geodesics to existence of regular curves which are
super-solutions of the radial null geodesic equation, and allows us to treat
all the known examples of naked singularities from a unified viewpoint. New
examples are also found using this approach, and perspectives are discussed.Comment: 8 pages, LaTeX2
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