75 research outputs found
Local Physical Coodinates from Symplectic Projector Method
The basic arguments underlying the symplectic projector method are presented.
By this method, local free coordinates on the constrait surface can be obtained
for a broader class of constrained systems. Some interesting examples are
analyzed.Comment: 8 page
Noncommutative fluid dynamics in the K\"{a}hler parametrization
In this paper, we propose a first order action functional for a large class
of systems that generalize the relativistic perfect fluids in the K\"{a}hler
parametrization to noncommutative spacetimes. We calculate the equations of
motion for the fluid potentials and the energy-momentum tensor in the first
order in the noncommutative parameter. The density current does not receive any
noncommutative corrections and it is conserved under the action of the
commutative generators but the energy-momentum tensor is not.
Therefore, we determine the set of constraints under which the energy-momentum
tensor is divergenceless. Another set of constraints on the fluid potentials is
obtained from the requirement of the invariance of the action under the
generalization of the volume preserving transformations of the noncommutative
spacetime. We show that the proposed action describes noncommutative fluid
models by casting the energy-momentum tensor in the familiar fluid form and
identifying the corresponding energy and momentum densities. In the commutative
limit, they are identical to the corresponding quantities of the relativistic
perfect fluids. The energy-momentum tensor contains a dissipative term that is
due to the noncommutative spacetime and vanishes in the commutative limit.
Finally, we particularize the theory to the case when the complex fluid
potentials are characterized by a function that is a deformation
of the complex plane and show that this model has important common features
with the commutative fluid such as infinitely many conserved currents and a
conserved axial current that in the commutative case is associated to the
topologically conserved linking number.Comment: References fixed. Typos corrected. 12 page
Time varying gravitational constant G via the entropic force
If the uncertainty principle applies to the Verlinde entropic idea, it leads
to a new term in the Newton's second law of mechanics in the Planck's scale.
This curious velocity dependence term inspires a frictional feature of the
gravity. In this short letter we address that this new term modifies the
effective mass and the Newtonian constant as the time dependence quantities.
Thus we must have a running on the value of the effective mass on the particle
mass near the holographic screen and the . This result has a nigh
relation with the Dirac hypothesis about the large numbers hypothesis (L.N.H.)
[1]. We propose that the corrected entropic terms via Verlinde idea can be
brought as a holographic evidence for the authenticity of the Dirac idea.Comment: Accepted for publication in "Communications in Theoretical Physics
(CTP)",Major revisio
Black Holes and Photons with Entropic Force
We study entropic force effects on black holes and photons. We find that
application of an entropic analysis restricts the radial change of a
black hole of radius , due to a test particle of a
Schwartzchild radius moving towards the black hole by near
black body surface, to be given by a relation , or {\Delta R}/{\lambdabar_M} = {\Delta x}/{2 \lambdabar_m}. We
suggest a new rule regarding entropy changes in different dimensions, \Delta
S= 2\pi k D \Delta l /\lambdabar, which unifies Verlinde's conjecture and the
black hole entropy formula. We also propose to extend the entropic force idea
to massless particles such as a photon. We find that there is an entropic force
on a photon of energy , with , and therefore
the photon has an effective gravitational mass .Comment: 4 Latex pages, no figure
Observables of the Euclidean Supergravity
The set of constraints under which the eigenvalues of the Dirac operator can
play the role of the dynamical variables for Euclidean supergravity is derived.
These constraints arise when the gauge invariance of the eigenvalues of the
Dirac operator is imposed. They impose conditions which restrict the
eigenspinors of the Dirac operator.Comment: Revised version, some misprints in the ecuations (11), (13) and (17)
corrected. The errors in the published version will appear cortected in a
future erratu
Euclidean Supergravity in Terms of Dirac Eigenvalues
It has been recently shown that the eigenvalues of the Dirac operator can be
considered as dynamical variables of Euclidean gravity. The purpose of this
paper is to explore the possiblity that the eigenvalues of the Dirac operator
might play the same role in the case of supergravity. It is shown that for this
purpose some primary constraints on covariant phase space as well as secondary
constraints on the eigenspinors must be imposed. The validity of primary
constraints under covariant transport is further analyzed. It is show that in
the this case restrictions on the tanget bundle and on the spinor bundle of
spacetime arise. The form of these restrictions is determined under some
simplifying assumptions. It is also shown that manifolds with flat curvature of
tangent bundle and spinor bundle and spinor bundle satisfy these restrictons
and thus they support the Dirac eigenvalues as global observables.Comment: Misprints and formulae corrected; to appear in Phys. Rev.
Higher Dimensional Recombination of Intersecting D-branes
We study recombinations of D-brane systems intersecting at more than one
angle using super Yang-Mills theory. We find the condensation of an
off-diagonal tachyon mode relates to the recombination, as was clarified for
branes at one angle in hep-th/0303204. For branes at two angles, after the
tachyon mode between two D2-branes condensed, D2-brane charge is distributed in
the bulk near the intersection point. We also find that, when two intersection
angles are equal, the off-diagonal lowest mode is massless, and a new stable
non-abelian configuration, which is supersymmetric up to a quadratic order in
the fluctuations, is obtained by the deformation by this mode.Comment: 18 pages, 2 figures, JHEP style. v3:references added, minor
corrections, English improve
EURONEAR - Recovery, Follow-up and Discovery of NEAs and MBAs using Large Field 1-2m Telescopes
We report on the follow-up and recovery of 100 program NEAs, PHAs and VIs
using the ESO/MPG 2.2m, Swope 1m and INT 2.5m telescopes equipped with large
field cameras. The 127 fields observed during 11 nights covered 29 square
degrees. Using these data, we present the incidental survey work which includes
558 known MBAs and 628 unknown moving objects mostly consistent with MBAs from
which 58 objects became official discoveries. We planned the runs using six
criteria and four servers which focus mostly on faint and poorly observed
objects in need of confirmation, follow-up and recovery. We followed 62 faint
NEAs within one month after discovery and we recovered 10 faint NEAs having big
uncertainties at their second or later opposition. Using the INT we eliminated
4 PHA candidates and VIs. We observed in total 1,286 moving objects and we
reported more than 10,000 positions. All data were reduced by the members of
our network in a team effort, and reported promptly to the MPC. The positions
of the program NEAs were published in 27 MPC and MPEC references and used to
improve their orbits. The O-C residuals for known MBAs and program NEAs are
smallest for the ESO/MPG and Swope and about four times larger for the INT
whose field is more distorted. The incidental survey allowed us to study
statistics of the MBA and NEA populations observable today with 1--2m
facilities. We calculate preliminary orbits for all unknown objects,
classifying them as official discoveries, later identifications and unknown
outstanding objects. The orbital elements a, e, i calculated by FIND_ORB
software for the official discoveries and later identified objects are very
similar with the published elements which take into account longer
observational arcs; thus preliminary orbits were used in statistics for the
whole unknown dataset. (CONTINUED)Comment: Accepted in Planetary and Space Science (Aug 2011
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