11,927 research outputs found
A Consistent Dark Matter Interpretation For CoGeNT and DAMA/LIBRA
In this paper, we study the recent excess of low energy events observed by
the CoGeNT collaboration and the annual modulation reported by the DAMA/LIBRA
collaboration, and discuss whether these signals could both be the result of
the same elastically scattering dark matter particle. We find that, without
channeling but when taking into account uncertainties in the relevant quenching
factors, a dark matter candidate with a mass of approximately ~7.0 GeV and a
cross section with nucleons of sigma_{DM-N} ~2x10^-4 pb (2x10^-40 cm^2) could
account for both of these observations. We also comment on the events recently
observed in the oxygen band of the CRESST experiment and point out that these
could potentially be explained by such a particle. Lastly, we compare the
region of parameter space favored by DAMA/LIBRA and CoGeNT to the constraints
from XENON 10, XENON 100, and CDMS (Si) and find that these experiments cannot
at this time rule out a dark matter interpretation of these signals.Comment: 8 pages, 6 figure
A new look at the problem of gauge invariance in quantum field theory
Quantum field theory is assumed to be gauge invariant. However it is well
known that when certain quantities are calculated using perturbation theory the
results are not gauge invariant. The non-gauge invariant terms have to be
removed in order to obtain a physically correct result. In this paper we will
examine this problem and determine why a theory that is supposed to be gauge
invariant produces non-gauge invariant results.Comment: Accepted by Physica Scripta. 27 page
Technical education and training: with special reference to developing countries
The typesetting book content by the jointed authors, D. D. Waters and J. W. Gailer
X-ray vs. Optical Variations in the Seyfert 1 Nucleus NGC 3516: A Puzzling Disconnectedness
We present optical broadband (B and R) observations of the Seyfert 1 nucleus
NGC 3516, obtained at Wise Observatory from March 1997 to March 2002,
contemporaneously with X-ray 2-10 keV measurements with RXTE. With these data
we increase the temporal baseline of this dataset to 5 years, more than triple
to the coverage we have previously presented for this object. Analysis of the
new data does not confirm the 100-day lag of X-ray behind optical variations,
tentatively reported in our previous work. Indeed, excluding the first year's
data, which drive the previous result, there is no significant correlation at
any lag between the X-ray and optical bands. We also find no correlation at any
lag between optical flux and various X-ray hardness ratios. We conclude that
the close relation observed between the bands during the first year of our
program was either a fluke, or perhaps the result of the exceptionally bright
state of NGC 3516 in 1997, to which it has yet to return. Reviewing the results
of published joint X-ray and UV/optical Seyfert monitoring programs, we
speculate that there are at least two components or mechanisms contributing to
the X-ray continuum emission up to 10 keV: a soft component that is correlated
with UV/optical variations on timescales >1 day, and whose presence can be
detected when the source is observed at low enough energies (about 1 keV), is
unabsorbed, or is in a sufficiently bright phase; and a hard component whose
variations are uncorrelated with the UV/optical.Comment: 9 pages, AJ, in pres
All-optical conditional logic with a nonlinear photonic crystal nanocavity
We demonstrate tunable frequency-converted light mediated by a chi-(2)
nonlinear photonic crystal nanocavity. The wavelength-scale InP-based cavity
supports two closely-spaced localized modes near 1550 nm which are resonantly
excited by a 130 fs laser pulse. The cavity is simultaneously irradiated with a
non-resonant probe beam, giving rise to rich second-order scattering spectra
reflecting nonlinear mixing of the different resonant and non-resonant
components. In particular, we highlight the radiation at the sum frequencies of
the probe beam and the respective cavity modes. This would be a useful,
minimally-invasive monitor of the joint occupancy state of multiple cavities in
an integrated optical circuit.Comment: 4 pages, 4 figure
Theoretical Models of Cyst Formation and Growth
Although the formation of fluid-filled, epithelial-lined cysts is a common event in a variety of tissues, the mechanisms involved are not well understood. Discussed here are means by which those mechanisms might be elucidated.
In general, there are too few data available for complete analysis of in vivo disease processes. It can be suggested only that epithelial proliferation and basement membrane growth are probably absolute requirements. Whether the forces for fluid accumulation precede or follow the stimuli for cell growth cannot be stated with certainty. On the other hand, in certain in vitro model systems the forces required to keep cyst cavities filled with fluid may be so small that cell growth, rather than fluid accumulation, seems the more likely primary event
Second-Order Nonlinear Mixing of Two Modes in a Planar Photonic Crystal Microcavity
Polarization-resolved second-harmonic spectra are obtained from the resonant
modes of a two-dimensional planar photonic crystal microcavity patterned in a
free-standing InP slab. The photonic crystal microcavity is comprised of a
single missing-hole defect in a hexagonal photonic crystal host formed with
elliptically-shaped holes. The cavity supports two orthogonally-polarized
resonant modes split by 60 wavenumbers. Sum-frequency data are reported from
the nonlinear interaction of the two coherently excited modes, and the
polarization dependence is explained in terms of the nonlinear susceptibility
tensor of the host InP.Comment: 7 pages, 8 Postscript figures, to be presented at Photonics West Jan.
2
Wormholes in String Theory
A wormhole is constructed by cutting and joining two spacetimes satisfying
the low energy string equations with a dilaton field. In spacetimes described
by the "string metric" the dilaton energy-momentum tensor need not satisfy the
weak or dominant energy conditions. In the cases considered here the dilaton
field violates these energy conditions and is the source of the exotic matter
required to maintain the wormhole. There is also a surface stress-energy, that
must be produced by additional matter, where the spacetimes are joined. It is
shown that wormholes can be constructed for which this additional matter
satisfies the weak and dominant energy conditions, so that it could be a form
of "normal" matter. Charged dilaton wormholes with a coupling between the
dilaton and the electromagnetic field that is more general than in string
theory are also briefly discussed.Comment: 9 pages, LaTex, submitted to Phys. Rev.
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