14,235 research outputs found
Teleparallel Spin Connection
A new expression for the spin connection of teleparallel gravity is proposed,
given by minus the contorsion tensor plus a zero connection. The corresponding
minimal coupling is covariant under local Lorentz transformation, and
equivalent to the minimal coupling prescription of general relativity. With
this coupling prescription, therefore, teleparallel gravity turns out to be
fully equivalent to general relativity, even in the presence of spinor fields.Comment: 2 pages, RevTeX, to appear in Phys. Rev D (Brief Report
Importance of Granular Structure in the Initial Conditions for the Elliptic Flow
We show effects of granular structure of the initial conditions (IC) of
hydrodynamic description of high-energy nucleus-nucleus collisions on some
observables, especially on the elliptic-flow parameter v2. Such a structure
enhances production of isotropically distributed high-pT particles, making v2
smaller there. Also, it reduces v2 in the forward and backward regions where
the global matter density is smaller, so where such effects become more
efficacious.Comment: 4 pages, 5 figure
Energy-momentum and angular momentum densities in gauge theories of gravity
In the \bar{\mbox{\rm Poincar\'{e}}} gauge theory of gravity, which has
been formulated on the basis of a principal fiber bundle over the space-time
manifold having the covering group of the proper orthochronous Poincar\'{e}
group as the structure group, we examine the tensorial properties of the
dynamical energy-momentum density and the ` `
spin" angular momentum density of the
gravitational field. They are both space-time vector densities, and transform
as tensors under {\em global} - transformations. Under {\em local}
internal translation, is invariant, while
transforms inhomogeneously. The dynamical
energy-momentum density and the ` ` spin"
angular momentum density of the matter field
are also examined, and they are known to be space-time vector densities and to
obey tensorial transformation rules under internal \bar{\mbox{\rm
Poincar\'{e}}} gauge transformations. The corresponding discussions in
extended new general relativity which is obtained as a teleparallel limit of
\bar{\mbox{\rm Poincar\'{e}}} gauge theory are also given, and
energy-momentum and ` ` spin" angular momentum densities are known to be well
behaved. Namely, they are all space-time vector densities, etc. In both
theories, integrations of these densities on a space-like surface give the
total energy-momentum and {\em total} (={\em spin}+{\em orbital}) angular
momentum for asymptotically flat space-time. The tensorial properties of
canonical energy-momentum and ` ` extended orbital angular momentum" densities
are also examined.Comment: 18 page
Endpoint of the Gregory-Laflamme instability of black strings revisited
We reproduce and extend the previous studies of Lehner and Pretorius of the endpoint of the Gregory-Laflamme instability of black strings in five space-time dimensions. We consider unstable black strings of fixed thickness and different lengths, and in all cases we confirm that at the intermediate stages of the evolution the horizon can be interpreted as a quasistationary self-similar sequence of black strings connecting spherical black holes on different scales. However, we do not find any evidence for a global timescale relating subsequent generations. The endpoint of the instability is the pinch off of the horizon in finite asymptotic time, thus confirming the violation of the weak cosmic censorship conjecture around black string spacetimes
Collaboration networks from a large CV database: dynamics, topology and bonus impact
Understanding the dynamics of research production and collaboration may
reveal better strategies for scientific careers, academic institutions and
funding agencies. Here we propose the use of a large and multidisciplinar
database of scientific curricula in Brazil, namely, the Lattes Platform, to
study patterns of scientific production and collaboration. In this database,
detailed information about publications and researchers are made available by
themselves so that coauthorship is unambiguous and individuals can be evaluated
by scientific productivity, geographical location and field of expertise. Our
results show that the collaboration network is growing exponentially for the
last three decades, with a distribution of number of collaborators per
researcher that approaches a power-law as the network gets older. Moreover,
both the distributions of number of collaborators and production per researcher
obey power-law behaviors, regardless of the geographical location or field,
suggesting that the same universal mechanism might be responsible for network
growth and productivity.We also show that the collaboration network under
investigation displays a typical assortative mixing behavior, where teeming
researchers (i.e., with high degree) tend to collaborate with others alike.
Finally, our analysis reveals that the distinctive collaboration profile of
researchers awarded with governmental scholarships suggests a strong bonus
impact on their productivity.Comment: 8 pages, 8 figure
Axial-Vector Torsion and the Teleparallel Kerr Spacetime
In the context of the teleparallel equivalent of general relativity, we
obtain the tetrad and the torsion fields of the stationary axisymmetric Kerr
spacetime. It is shown that, in the slow rotation and weak field
approximations, the axial-vector torsion plays the role of the gravitomagnetic
component of the gravitational field, and is thus the responsible for the
Lense-Thirring effect.Comment: 9 pages, no figures, to appear in Class. Quant. Gra
- …