14,205 research outputs found
How the orbital period of a test particle is modified by the Dvali-Gabadadze-Porrati gravity?
In addition to the pericentre \omega, the mean anomaly M and, thus, the mean
longitude \lambda, also the orbital period Pb and the mean motion of a test
particle are modified by the Dvali-Gabadadze-Porrati gravity. While the
correction to Pb depends on the mass of the central body and on the geometrical
features of the orbital motion around it, the correction to is independent
of them, up to terms of second order in the eccentricity . The latter one
amounts to about 2\times 10^-3 arcseconds per century. The present-day accuracy
in determining the mean motions of the inner planets of the Solar System from
radar ranging and differential Very Long Baseline Interferometry is
10^-2-5\times 10^-3 arcseconds per century, but it should be improved in the
near future when the data from the spacecraft to Mercury and Venus will be
available.Comment: LaTex, 7 pages, 13 references, no tables, no figures. Section 2.3
added. To appear in JCA
Reduction for constrained variational problems on 3D null curves
We consider the optimal control problem for null curves in de Sitter 3-space
defined by a functional which is linear in the curvature of the trajectory. We
show how techniques based on the method of moving frames and exterior
differential systems, coupled with the reduction procedure for systems with a
Lie group of symmetries lead to the integration by quadratures of the
extremals. Explicit solutions are found in terms of elliptic functions and
integrals.Comment: 16 page
Secular increase of the Astronomical Unit and perihelion precessions as tests of the Dvali-Gabadadze-Porrati multi-dimensional braneworld scenario
An unexpected secular increase of the Astronomical Unit, the length scale of
the Solar System, has recently been reported by three different research groups
(Krasinsky and Brumberg, Pitjeva, Standish). The latest JPL measurements amount
to 7+-2 m cy^-1. At present, there are no explanations able to accommodate such
an observed phenomenon, neither in the realm of classical physics nor in the
usual four-dimensional framework of the Einsteinian General Relativity. The
Dvali-Gabadadze-Porrati braneworld scenario, which is a multi-dimensional model
of gravity aimed to the explanation of the observed cosmic acceleration without
dark energy, predicts, among other things, a perihelion secular shift, due to
Lue and Starkman, of 5 10^-4 arcsec cy^-1 for all the planets of the Solar
System. It yields a variation of about 6 m cy^-1 for the Earth-Sun distance
which is compatible at 1-sigma level with the observed rate of the Astronomical
Unit. The recently measured corrections to the secular motions of the perihelia
of the inner planets of the Solar System are in agreement, at 1-sigma level,
with the predicted value of the Lue-Starkman effect for Mercury and Mars and at
2-sigma level for the Earth.Comment: LaTex2e, 7 pages, no figures, no tables, 13 references. Minor
correction
The intrinsic three-dimensional shape of galactic bars
We present the first statistical study on the intrinsic three-dimensional
(3D) shape of a sample of 83 galactic bars extracted from the CALIFA survey. We
use the galaXYZ code to derive the bar intrinsic shape with a statistical
approach. The method uses only the geometric information (ellipticities and
position angles) of bars and discs obtained from a multi-component photometric
decomposition of the galaxy surface-brightness distributions. We find that bars
are predominantly prolate-triaxial ellipsoids (68%), with a small fraction of
oblate-triaxial ellipsoids (32%). The typical flattening (intrinsic C/A
semiaxis ratio) of the bars in our sample is 0.34, which matches well the
typical intrinsic flattening of stellar discs at these galaxy masses. We
demonstrate that, for prolate-triaxial bars, the intrinsic shape of bars
depends on the galaxy Hubble type and stellar mass (bars in massive S0 galaxies
are thicker and more circular than those in less massive spirals). The bar
intrinsic shape correlates with bulge, disc, and bar parameters. In particular
with the bulge-to-total (B/T) luminosity ratio, disc g-r color, and central
surface brightness of the bar, confirming the tight link between bars and their
host galaxies. Combining the probability distributions of the intrinsic shape
of bulges and bars in our sample we show that 52% (16%) of bulges are thicker
(flatter) than the surrounding bar at 1 level. We suggest that these
percentages might be representative of the fraction of classical and disc-like
bulges in our sample, respectively.Comment: 18 pages, 11 figures, accepted for publication in MNRA
The out-equilibrium 2D Ising spin glass: almost, but not quite, a free-field theory
We consider the spatial correlation function of the two-dimensional Ising
spin glass under out-equilibrium conditions. We pay special attention to the
scaling limit reached upon approaching zero temperature. The field-theory of a
non-interacting field makes a surprisingly good job at describing the spatial
shape of the correlation function of the out-equilibrium Edwards-Anderson Ising
model in two dimensions.Comment: 20 pages + 5 Figure
Resonant X-ray diffraction studies on the charge ordering in magnetite
Here we show that the low temperature phase of magnetite is associated with
an effective, although fractional, ordering of the charge. Evidence and a
quantitative evaluation of the atomic charges are achieved by using resonant
x-ray diffraction (RXD) experiments whose results are further analyzed with the
help of ab initio calculations of the scattering factors involved. By
confirming the results obtained from X-ray crystallography we have shown that
RXD is able to probe quantitatively the electronic structure in very complex
oxides, whose importance covers a wide domain of applications.Comment: 4 pages 4 figures, accepted for publication in PR
Relaxation time spectrum of low-energy excitations in one- and two-dimensional materials with charge or spin density waves
The long-time thermal relaxation of (TMTTF)Br, SrCuO
and SrCaCuO single crystals at temperatures below 1 K
and magnetic field up to 10 T is investigated. The data allow us to determine
the relaxation time spectrum of the low energy excitations caused by the
charge-density wave (CDW) or spin-density wave (SDW). The relaxation time is
mainly determined by a thermal activated process for all investigated
materials. The maximum relaxation time increases with increasing magnetic
field. The distribution of barrier heights corresponds to one or two Gaussian
functions. The doping of SrCaCuO with Ca leads to
a drastic shift of the relaxation time spectrum to longer time. The maximum
relaxation time changes from 50 s (x = 0) to 3000 s (x = 12) at 0.1 K and 10 T.
The observed thermal relaxation at x=12 clearly indicates the formation of the
SDW ground state at low temperatures
Optimization by Quantum Annealing: Lessons from Simple Cases
This paper investigates the basic behavior and performance of simulated
quantum annealing (QA) in comparison with classical annealing (CA). Three
simple one dimensional case study systems are considered, namely a parabolic
well, a double well, and a curved washboard. The time dependent Schr\"odinger
evolution in either real or imaginary time describing QA is contrasted with the
Fokker Planck evolution of CA. The asymptotic decrease of excess energy with
annealing time is studied in each case, and the reasons for differences are
examined and discussed. The Huse-Fisher classical power law of double well CA
is replaced with a different power law in QA. The multi-well washboard problem
studied in CA by Shinomoto and Kabashima and leading classically to a
logarithmic annealing even in the absence of disorder, turns to a power law
behavior when annealed with QA. The crucial role of disorder and localization
is briefly discussed.Comment: 16 pages, 9 figure
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