74 research outputs found
Classical Evolution of Quantum Elliptic States
The hydrogen atom in weak external fields is a very accurate model for the
multiphoton excitation of ultrastable high angular momentum Rydberg states, a
process which classical mechanics describes with astonishing precision. In this
paper we show that the simplest treatment of the intramanifold dynamics of a
hydrogenic electron in external fields is based on the elliptic states of the
hydrogen atom, i.e., the coherent states of SO(4), which is the dynamical
symmetry group of the Kepler problem. Moreover, we also show that classical
perturbation theory yields the {\it exact} evolution in time of these quantum
states, and so we explain the surprising match between purely classical
perturbative calculations and experiments. Finally, as a first application, we
propose a fast method for the excitation of circular states; these are
ultrastable hydrogenic eigenstates which have maximum total angular momentum
and also maximum projection of the angular momentum along a fixed direction. %Comment: 8 Pages, 2 Figures. Accepted for publication in Phys. Rev.
-Strands
A -strand is a map for a Lie
group that follows from Hamilton's principle for a certain class of
-invariant Lagrangians. The SO(3)-strand is the -strand version of the
rigid body equation and it may be regarded physically as a continuous spin
chain. Here, -strand dynamics for ellipsoidal rotations is derived as
an Euler-Poincar\'e system for a certain class of variations and recast as a
Lie-Poisson system for coadjoint flow with the same Hamiltonian structure as
for a perfect complex fluid. For a special Hamiltonian, the -strand is
mapped into a completely integrable generalization of the classical chiral
model for the SO(3)-strand. Analogous results are obtained for the
-strand. The -strand is the -strand version of the
Bloch-Iserles ordinary differential equation, whose solutions exhibit dynamical
sorting. Numerical solutions show nonlinear interactions of coherent wave-like
solutions in both cases. -strand equations on the
diffeomorphism group are also introduced and shown
to admit solutions with singular support (e.g., peakons).Comment: 35 pages, 5 figures, 3rd version. To appear in J Nonlin Sc
Stringent Constraints on Cosmological Neutrino-Antineutrino Asymmetries from Synchronized Flavor Transformation
We assess a mechanism which can transform neutrino-antineutrino asymmetries
between flavors in the early universe, and confirm that such transformation is
unavoidable in the near bi-maximal framework emerging for the neutrino mixing
matrix. We show that the process is a standard Mikheyev-Smirnov-Wolfenstein
flavor transformation dictated by a synchronization of momentum states. We also
show that flavor ``equilibration'' is a special feature of maximal mixing, and
carefully examine new constraints placed on neutrino asymmetries. In
particular, the big bang nucleosynthesis limit on electron neutrino degeneracy
xi_e < 0.04 does not apply directly to all flavors, yet confirmation of the
large-mixing-angle solution to the solar neutrino problem will eliminate the
possibility of degenerate big bang nucleosynthesis.Comment: 11 pages, 6 figures; minor changes to match PRD versio
Comparison of Recent SnIa datasets
We rank the six latest Type Ia supernova (SnIa) datasets (Constitution (C),
Union (U), ESSENCE (Davis) (E), Gold06 (G), SNLS 1yr (S) and SDSS-II (D)) in
the context of the Chevalier-Polarski-Linder (CPL) parametrization
, according to their Figure of Merit (FoM), their
consistency with the cosmological constant (CDM), their consistency
with standard rulers (Cosmic Microwave Background (CMB) and Baryon Acoustic
Oscillations (BAO)) and their mutual consistency. We find a significant
improvement of the FoM (defined as the inverse area of the 95.4% parameter
contour) with the number of SnIa of these datasets ((C) highest FoM, (U), (G),
(D), (E), (S) lowest FoM). Standard rulers (CMB+BAO) have a better FoM by about
a factor of 3, compared to the highest FoM SnIa dataset (C). We also find that
the ranking sequence based on consistency with CDM is identical with
the corresponding ranking based on consistency with standard rulers ((S) most
consistent, (D), (C), (E), (U), (G) least consistent). The ranking sequence of
the datasets however changes when we consider the consistency with an expansion
history corresponding to evolving dark energy crossing the
phantom divide line (it is practically reversed to (G), (U), (E), (S),
(D), (C)). The SALT2 and MLCS2k2 fitters are also compared and some peculiar
features of the SDSS-II dataset when standardized with the MLCS2k2 fitter are
pointed out. Finally, we construct a statistic to estimate the internal
consistency of a collection of SnIa datasets. We find that even though there is
good consistency among most samples taken from the above datasets, this
consistency decreases significantly when the Gold06 (G) dataset is included in
the sample.Comment: 13 pages, 9 figures. Included recently released SDSS-II dataset.
Improved presentation. Main results unchanged. The mathematica files and
datasets used for the production of the figures may be downloaded from
http://leandros.physics.uoi.gr/datacomp
Does accelerating universe indicates Brans-Dicke theory
The evolution of universe in Brans-Dicke (BD) theory is discussed in this
paper.
Considering a parameterized scenario for BD scalar field
which plays the role of gravitational "constant" ,
we apply the Markov Chain Monte Carlo method to investigate a global
constraints on BD theory with a self-interacting potential according to the
current observational data: Union2 dataset of type supernovae Ia (SNIa),
high-redshift Gamma-Ray Bursts (GRBs) data, observational Hubble data (OHD),
the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and
the cosmic microwave background (CMB) data. It is shown that an expanded
universe from deceleration to acceleration is given in this theory, and the
constraint results of dimensionless matter density and parameter
are, and
which is consistent with the
result of current experiment exploration, . In
addition, we use the geometrical diagnostic method, jerk parameter , to
distinguish the BD theory and cosmological constant model in Einstein's theory
of general relativity.Comment: 16 pages, 3 figure
Density perturbations in generalized Einstein scenarios and constraints on nonminimal couplings from the Cosmic Microwave Background
We study cosmological perturbations in generalized Einstein scenarios and
show the equivalence of inflationary observables both in the Jordan frame and
the Einstein frame. In particular the consistency relation relating the
tensor-to-scalar ratio with the spectral index of tensor perturbations
coincides with the one in Einstein gravity, which leads to the same likelihood
results in terms of inflationary observables. We apply this formalism to
nonminimally coupled chaotic inflationary scenarios with potential
and place constraints on the strength of nonminimal couplings using a
compilation of latest observational data. In the case of the quadratic
potential (), the nonminimal coupling is constrained to be for negative from the observational contour
bound. Although the quartic potential () is under a strong observational
pressure for , this property is relaxed by taking into account negative
nonminimal couplings. We find that inflationary observables are within the
contour bound as long as . We also show that
the cases are disfavoured even in the presence of nonminimal
couplings.Comment: 16 pages, 4 eps figure
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Structural analysis of oligomeric molecules formed from the reaction products of oleic acid ozonolysis
The products arising from the ozonolysis of oleic acid (cis-9-octadecenoic acid) in solution have been studied using negative ion mode electrospray ionization ion trap mass spectrometry. Oleic acid is an important component of atmospheric organic aerosol and is a key model species in predicting aerosol physical and chemical characteristics. The four predicted reaction products, 1-nonanal, nonanoic acid, 9-oxononanoic acid, and azelaic acid, were all observed in roughly equal yields. In addition to these products a large number of higher molecular weight compounds were detected with m/z ratios of up to 1000 Daltons. Tandem mass spectrometry of these larger ions revealed that they represented a complex mixture of linear α-acyloxyalkyl hydroperoxides, secondary ozonides, and cyclic diperoxides, formed by reactions between ozonolysis products and Criegee intermediates. These comprise the first directly elucidated structures of large oligomeric species from oleic acid ozonolysis. The degree of oligomerization and hence molecular weight distribution was observed to increase with reaction time in solution
The link between copper and Wilsonâs disease
Wilsonâs disease (hepatolenticular degeneration) is a rare inherited autosomal recessive disorder of copper metabolism leading to copper accumulation in the liver and extrahepatic organs such as the brain and cornea. Patients may present with combinations of hepatic, neurological and psychiatric symptoms. Copper is the therapeutic target for the treatment of Wilsonâs disease. But how did copper come to be linked with Wilsonâs disease? The answer encompasses a study of enzootic neonatal ataxia in lambs in the 1930s, the copper-chelating properties of British Anti-Lewisite, and the chemical analysis for copper of the organs of deceased Wilsonâs disease patients in the mid-to-late 1940s. Wilsonâs disease is one of a number of copper-related disorders where loss of copper homeostasis as a result of genetic, nutritional or environmental factors affects human health
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