6,453 research outputs found
Flux-limited strong gravitational lensing and dark energy
In the standard flat cosmological constant () cold dark matter (CDM)
cosmology, a model of two populations of lens halos for strong gravitational
lensing can reproduce the results of the Jodrell-Bank VLA Astrometric Survey
(JVAS) and the Cosmic Lens All-Sky Survey (CLASS) radio survey. In such a
model, lensing probabilities are sensitive to three parameters: the
concentration parameter , the cooling mass scale and the
value of the CDM power spectrum normalization parameter . The value
ranges of these parameters are constrained by various observations. However, we
found that predicted lensing probabilities are also quite sensitive to the flux
density (brightness) ratio of the multiple lensing images,
which has been, in fact, a very important selection criterion of a sample in
any lensing survey experiments. We re-examine the above mentioned model by
considering the flux ratio and galactic central Super Massive Black Holes
(SMBHs), in flat, low-density cosmological models with different cosmic
equations of state , and find that the predicted lensing probabilities
without considering are over-estimated. A low value of
can be compensated by raising the cooling mass scale
in fitting the predicted lensing probabilities to JVAS/CLASS
observations. In order to determine the cosmic equation of state , the
uncertainty in must be resolved. The effects of SMBHs cannot be
detected by strong gravitational lensing method when .Comment: 7 pages, 2 figures, corrected to match published version in A&
Torsion fields generated by the quantum effects of macro-bodies
We generalize Einstein's General Relativity (GR) by assuming that all matter
(including macro-objects) has quantum effects. An appropriate theory to fulfill
this task is Gauge Theory Gravity (GTG) developed by the Cambridge group. GTG
is a ``spin-torsion" theory, according to which, gravitational effects are
described by a pair of gauge fields defined over a flat Minkowski background
spacetime. The matter content is completely described by the Dirac spinor
field, and the quantum effects of matter are identified as the spin tensor
derived from the spinor field. The existence of the spin of matter results in
the torsion field defined over spacetime. Torsion field plays the role of
Bohmian quantum potential which turns out to be a kind of repulsive force as
opposed to the gravitational potential which is attractive. The equivalence
principle remains and essential in this theory so that GR is relegated to a
locally approximate theory wherein the quantum effects (torsion) are
negligible. As a toy model, we assume that the macro matter content can be
described by the covariant Dirac equation and apply this theory to the simplest
radially symmetric and static gravitational systems. Consequently, by virtue of
the cosmological principle, we are led to a static universe model in which the
Hubble redshifts arise from the torsion fields.Comment: 21 pages, some missing symbols added and the errors in grammar
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