1,489 research outputs found
What is there in the black box of dark energy: variable cosmological parameters or multiple (interacting) components?
The coincidence problems and other dynamical features of dark energy are
studied in cosmological models with variable cosmological parameters and in
models with the composite dark energy. It is found that many of the problems
usually considered to be cosmological coincidences can be explained or
significantly alleviated in the aforementioned models.Comment: 6 pages, 1 figure, talk given at IRGAC2006 (Barcelona, July 11-15,
2006), to appear in J. Phys.
Dark energy: a quantum fossil from the inflationary Universe?
The discovery of dark energy (DE) as the physical cause for the accelerated
expansion of the Universe is the most remarkable experimental finding of modern
cosmology. However, it leads to insurmountable theoretical difficulties from
the point of view of fundamental physics. Inflation, on the other hand,
constitutes another crucial ingredient, which seems necessary to solve other
cosmological conundrums and provides the primeval quantum seeds for structure
formation. One may wonder if there is any deep relationship between these two
paradigms. In this work, we suggest that the existence of the DE in the present
Universe could be linked to the quantum field theoretical mechanism that may
have triggered primordial inflation in the early Universe. This mechanism,
based on quantum conformal symmetry, induces a logarithmic,
asymptotically-free, running of the gravitational coupling. If this evolution
persists in the present Universe, and if matter is conserved, the general
covariance of Einstein's equations demands the existence of dynamical DE in the
form of a running cosmological term whose variation follows a power law of the
redshift.Comment: LaTeX, 14 pages, extended discussion. References added. Accepted in
J. Phys. A: Mathematical and Theoretica
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Observations of Past Lunar Landing Sites by the D-CIXS X-Ray Spectrometer on SMART-1
D-CIXS initial observations show a first unambiguous remote sensing of calcium in the lunar regolith. Data obtained are broadly consistent with current understanding of mare and highland composition. Ground truth is provided by the returned Apollo and Luna sample sets
Cosmic perturbations with running G and Lambda
Cosmologies with running cosmological term (Lambda) and gravitational
Newton's coupling (G) may naturally be expected if the evolution of the
universe can ultimately be derived from the first principles of Quantum Field
Theory or String Theory. In this paper, we derive the general cosmological
perturbation equations for models with variable G and Lambda in which the
fluctuations in both variables are explicitly included. We demonstrate that, if
matter is covariantly conserved, the late growth of matter density
perturbations is independent of the wavenumber. Furthermore, if Lambda is
negligible at high redshifts and G varies slowly, we find that these
cosmologies produce a matter power spectrum with the same shape as that of the
concordance LCDM model, thus predicting the same basic features on structure
formation. Despite this shape indistinguishability, the free parameters of the
variable G and Lambda models can still be effectively constrained from the
observational bounds on the spectrum amplitude.Comment: Accepted in Classical and Quantum Gravity. One appendix on
perturbations in the Newtonian gauge added. Extended discussion and new
references
Shedding New Light on Kaon-Nucleon/Nuclei Interaction and Its Astrophysical Implications with the AMADEUS Experiment at DAFNE
The AMADEUS experiment deals with the investigation of the low-energy
kaon-nuclei hadronic interaction at the DA{\Phi}NE collider at LNF-INFN, which
is fundamental to respond longstanding questions in the non-perturbative QCD
strangeness sector. The antikaon-nucleon potential is investigated searching
for signals from possible bound kaonic clusters, which would open the
possibility for the formation of cold dense baryonic matter. The confirmation
of this scenario may imply a fundamental role of strangeness in astrophysics.
AMADEUS step 0 consisted in the reanalysis of 2004/2005 KLOE dataset,
exploiting K- absorptions in H, 4He, 9Be and 12C in the setup materials. In
this paper, together with a review on the multi-nucleon K- absorption and the
particle identification procedure, the first results on the {\Sigma}0-p channel
will be presented including a statistical analysis on the possible accomodation
of a deeply bound stateComment: 6 pages, 2 figure, 1 table, HADRON 2015 conferenc
Tooth development and replacement in the Atlantic Cutlassfish, Trichiurus lepturus, with comparisons to other Scombroidei
Atlantic Cutlassfish, Trichiurus lepturus, have large, barbed, premaxillary and dentary fangs, and sharp dagger-shaped teeth in their oral jaws. Functional teeth firmly ankylose to the dentigerous bones. We used dry skeletons, histology, SEM, and micro-CT scanning to study 92 specimens of T. lepturus from the western North Atlantic to describe its dentition and tooth replacement. We identified three modes of intraosseous tooth replacement in T. lepturus depending on the location of the tooth in the jaw. Mode 1 relates to replacement of premaxillary fangs, in which new tooth germs enter the lingual surface of the premaxilla, develop horizontally, and rotate into position. We suggest that growth of large fangs in the premaxilla is accommodated by this horizontal development. Mode 2 occurs for dentary fangs: new tooth germs enter the labial surface of the dentary, develop vertically, and erupt into position. Mode 3 describes replacement of lateral teeth, in which new tooth germs enter a trench along the crest of the dentigerous bone, develop vertically, and erupt into position. Such distinct modes of tooth replacement in a teleostean species are unknown. We compared modes of replacement in T. lepturus to 20 species of scombroids to explore the phylogenetic distribution of these three replacement modes. Alternate tooth replacement (in which new teeth erupt between two functional teeth), ankylosis, and intraosseous tooth development are plesiomorphic to Bluefish + other Scombroidei. Our study highlights the complexity and variability of intraosseous tooth replacement. Within tooth replacement systems, key variables include sites of formation of tooth germs, points of entry of tooth germs into dentigerous bones, coupling of tooth germ migration and bone erosion, whether teeth develop horizontally or immediately beneath the tooth to be replaced, and how tooth eruption and ankylosis occur. Developmentally different tooth replacement processes can yield remarkably similar dentitions
Features of Muon Arrival Time Distributions of High Energy EAS at Large Distances From the Shower Axis
In view of the current efforts to extend the KASCADE experiment
(KASCADE-Grande) for observations of Extensive Air Showers (EAS) of primary
energies up to 1 EeV, the features of muon arrival time distributions and their
correlations with other observable EAS quantities have been scrutinised on
basis of high-energy EAS, simulated with the Monte Carlo code CORSIKA and using
in general the QGSJET model as generator. Methodically various correlations of
adequately defined arrival time parameters with other EAS parameters have been
investigated by invoking non-parametric methods for the analysis of
multivariate distributions, studying the classification and misclassification
probabilities of various observable sets. It turns out that adding the arrival
time information and the multiplicity of muons spanning the observed time
distributions has distinct effects improving the mass discrimination. A further
outcome of the studies is the feature that for the considered ranges of primary
energies and of distances from the shower axis the discrimination power of
global arrival time distributions referring to the arrival time of the shower
core is only marginally enhanced as compared to local distributions referring
to the arrival of the locally first muon.Comment: 24 pages, Journal Physics G accepte
Lunar chemistry from Chandrayaan-1, C1XS results from Southern nearside highlands of the Moon
This article does not have an abstract
Calibration of the length of a chain of single gold atoms
Using a scanning tunneling microscope or mechanically controllable break
junctions it has been shown that it is possible to control the formation of a
wire made of single gold atoms. In these experiments an interatomic distance
between atoms in the chain of ~3.6 Angstrom was reported which is not
consistent with recent theoretical calculations. Here, using precise
calibration procedures for both techniques, we measure length of the atomic
chains. Based on the distance between the peaks observed in the chain length
histogram we find the mean value of the inter-atomic distance before chain
rupture to be 2.6 +/- 0.2 A . This value agrees with the theoretical
calculations for the bond length. The discrepancy with the previous
experimental measurements was due to the presence of He gas, that was used to
promote the thermal contact, and which affects the value of the work function
that is commonly used to calibrate distances in scanning tunnelling microscopy
and mechanically controllable break junctions at low temperatures.Comment: 6 pages, 6 figure
The second flight of the SUNRISE balloon-borne solar observatory: overview of instrument updates, the flight, the data and first results
The SUNRISE balloon-borne solar observatory, consisting of a 1~m aperture
telescope that provided a stabilized image to a UV filter imager and an imaging
vector polarimeter, carried out its second science flight in June 2013. It
provided observations of parts of active regions at high spatial resolution,
including the first high-resolution images in the Mg~{\sc ii}~k line. The
obtained data are of very high quality, with the best UV images reaching the
diffraction limit of the telescope at 3000~\AA\ after Multi-Frame Blind
Deconvolution reconstruction accounting for phase-diversity information. Here a
brief update is given of the instruments and the data reduction techniques,
which includes an inversion of the polarimetric data. Mainly those aspects that
evolved compared with the first flight are described. A tabular overview of the
observations is given. In addition, an example time series of a part of the
emerging active region NOAA AR~11768 observed relatively close to disk centre
is described and discussed in some detail. The observations cover the pores in
the trailing polarity of the active region, as well as the polarity inversion
line where flux emergence was ongoing and a small flare-like brightening
occurred in the course of the time series. The pores are found to contain
magnetic field strengths ranging up to 2500~G and, while large pores are
clearly darker and cooler than the quiet Sun in all layers of the photosphere,
the temperature and brightness of small pores approach or even exceed those of
the quiet Sun in the upper photosphere.Comment: Accepted for publication in The Astrophysical Journa
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