1,185 research outputs found
On Poincar\'e gauge theory of gravity, its equations of motion, and Gravity Probe B
Ever since E.Cartan in the 1920s enriched the geometric framework of general
relativity (GR) by introducing a {\it torsion} of spacetime, the question arose
whether one could find a measurement technique for detecting the presence of a
torsion field. Mao et al.(2007) claimed that the rotating quartz balls in the
gyroscopes of the Gravity Probe B experiment, falling freely on an orbit around
the Earth, should "feel" the torsion. Similarly, March et al.(2011) argue with
the precession of the Moon and the Mercury and extend later their
considerations to the Lageos satellite.--- A consistent theory of gravity with
torsion emerged during the early 1960's as gauge theory of the Poincar\'e
group. This Poincar\'e gauge theory of gravity incorporates as simplest viable
cases the Einstein-Cartan(-Sciama-Kibble) theory (EC), the teleparallel
equivalent GR|| of GR, and GR itself. So far, PG and, in particular, the
existence of torsion have {\it not} been experimentally confirmed. However, PG
is to be considered as the standard theory of gravity with torsion because of
its very convincing gauge structure.--- Since the early 1970s up to today,
different groups have shown more or less independently that torsion couples
only to the {\it elementary particle spin} and under no circumstances to the
orbital angular momentum of test particles. This is established knowledge and
we reconfirm this conclusion by discussing the energy-momentum law of PG, which
has same form for all versions of PG. Therefore, we conclude that,
unfortunately, the investigations of Mao et al. and March et al. do not yield
any information on torsion.Comment: 7 pages of latex with 2 figures, title changed, minor corrections
inserted, some references adde
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Neutrino-driven winds in the aftermath of a neutron star merger: nucleosynthesis and electromagnetic transients
We present a comprehensive nucleosynthesis study of the neutrino-driven wind
in the aftermath of a binary neutron star merger. Our focus is the initial
remnant phase when a massive central neutron star is present. Using tracers
from a recent hydrodynamical simulation, we determine total masses and
integrated abundances to characterize the composition of unbound matter. We
find that the nucleosynthetic yields depend sensitively on both the life time
of the massive neutron star and the polar angle. Matter in excess of up to becomes unbound until . Due to
electron fractions of mainly nuclei with mass
numbers are synthesized, complementing the yields from the earlier
dynamic ejecta. Mixing scenarios with these two types of ejecta can explain the
abundance pattern in r-process enriched metal-poor stars. Additionally, we
calculate heating rates for the decay of the freshly produced radioactive
isotopes. The resulting light curve peaks in the blue band after about . Furthermore, high opacities due to heavy r-process nuclei in the dynamic
ejecta lead to a second peak in the infrared after .Comment: 15 pages, 18 figures, 2 tables, accepted by Ap
Adolescents' attitudes towards foreigners: associations with perceptions of significant others' attitudes depending on sex and age
'The present study examines associations between adolescents' attitudes towards foreigners and their perceptions of the same attitudes among their parents, friends, and teachers. Questionnaire data from a sample of 518 students attending 6th, 8th, 10th, and 12th grade of German high-track schools addressed students' own attitudes and their reports on the reference persons m their proximal contexts. Analyses of individual profile correlations suggest strong correspondences between adolescents and their perceived contexts which slightly decrease depending on age. Processes of projection are discussed as a possible explanation of the strong associations observed as well as to the age-graded pattern of correlations.' (author's abstract)
Complete determination of molecular orbitals by measurement of phase symmetry and electron density.
Several experimental methods allow measuring the spatial probability density of electrons in atoms, molecules and solids, that is, the absolute square of the respective single-particle wave function. But it is an intrinsic problem of the measurement process that the information about the phase is generally lost during the experiment. The symmetry of this phase, however, is a crucial parameter for the knowledge of the full orbital information in real space. Here, we report on a key experiment that demonstrates that the phase symmetry can be derived from a strictly experimental approach from the circular dichroism in the angular distribution of photoelectrons. In combination with the electron density derived from the same experiment, the full quantum mechanical wave function can thus be determined experimentally
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