16,762 research outputs found
Exclusive Lambda_b -> Lambda l^+ l^- decay in two Higgs doublet model
Rare Lambda_b -> Lambda l^+ l^- decay is investigated in framework of general
two Higgs doublet model, in which a new source of CP violation exists (model
III). The polarization parameter, CP asymmetry and decay width are calculated.
It is shown that CP asymmetry is a very sensitive tool for establishing model
III.Comment: 16 pages, 3 figures, LaTeX formatte
The meson annihilation to leptons and inclusive light hadrons
The annihilation of the meson to leptons and inclusive light hadrons is
analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find
that the decay mode, which escapes from the helicity suppression, contributes a
sizable fraction width. According to the analysis, the branching ratio due to
the contribution from the color-singlet component of the meson can be of
order (10^{-2}). We also estimate the contributions from the color-octet
components. With the velocity scaling rule of NRQCD, we find that the
color-octet contributions are sizable too, especially, in certain phase space
of the annihilation they are greater than (or comparative to) the color-singlet
component. A few observables relevant to the spectrum of charged lepton are
suggested, that may be used as measurements on the color-octet and
color-singlet components in the future experiments. A typical long
distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.
Mechanisms for electron transport in atomic-scale one-dimensional wires: soliton and polaron effects
We study one-electron tunneling through atomic-scale one-dimensional wires in
the presence of coherent electron-phonon (e-ph) coupling. We use a full quantum
model for the e-ph interaction within the wire with open boundary conditions.
We illustrate the mechanisms of transport in the context of molecular wires
subject to boundary conditions imposing the presence of a soliton defect in the
molecule. Competition between polarons and solitons in the coherent transport
is examined. The transport mechanisms proposed are generally applicable to
other one-dimensional nanoscale systems with strong e-ph coupling.Comment: 7 pages, 4 figures, accepted for publication in Europhys. Let
Tracking system analytic calibration activities for the Mariner Mars 1969 mission
Calibration activity of Deep Space Network in support of Mars encounter phase of Mariner Mars 1969 missio
Deciphering the enigma of undetected species, phylogenetic, and functional diversity based on Good-Turing theory
Estimating the species, phylogenetic, and functional diversity of a community is challenging because rare species are often undetected, even with intensive sampling. The Good-Turing frequency formula, originally developed for cryptography, estimates in an ecological context the true frequencies of rare species in a single assemblage based on an incomplete sample of individuals. Until now, this formula has never been used to estimate undetected species, phylogenetic, and functional diversity. Here, we first generalize the Good-Turing formula to incomplete sampling of two assemblages. The original formula and its two-assemblage generalization provide a novel and unified approach to notation, terminology, and estimation of undetected biological diversity. For species richness, the Good-Turing framework offers an intuitive way to derive the non-parametric estimators of the undetected species richness in a single assemblage, and of the undetected species shared between two assemblages. For phylogenetic diversity, the unified approach leads to an estimator of the undetected Faith\u27s phylogenetic diversity (PD, the total length of undetected branches of a phylogenetic tree connecting all species), as well as a new estimator of undetected PD shared between two phylogenetic trees. For functional diversity based on species traits, the unified approach yields a new estimator of undetected Walker et al.\u27s functional attribute diversity (FAD, the total species-pairwise functional distance) in a single assemblage, as well as a new estimator of undetected FAD shared between two assemblages. Although some of the resulting estimators have been previously published (but derived with traditional mathematical inequalities), all taxonomic, phylogenetic, and functional diversity estimators are now derived under the same framework. All the derived estimators are theoretically lower bounds of the corresponding undetected diversities; our approach reveals the sufficient conditions under which the estimators are nearly unbiased, thus offering new insights. Simulation results are reported to numerically verify the performance of the derived estimators. We illustrate all estimators and assess their sampling uncertainty with an empirical dataset for Brazilian rain forest trees. These estimators should be widely applicable to many current problems in ecology, such as the effects of climate change on spatial and temporal beta diversity and the contribution of trait diversity to ecosystem multi-functionality
Fragmentation of Nuclei at Intermediate and High Energies in Modified Cascade Model
The process of nuclear multifragmentation has been implemented, together with
evaporation and fission channels of the disintegration of excited remnants in
nucleus-nucleus collisions using percolation theory and the intranuclear
cascade model. Colliding nuclei are treated as face--centered--cubic lattices
with nucleons occupying the nodes of the lattice. The site--bond percolation
model is used. The code can be applied for calculation of the fragmentation of
nuclei in spallation and multifragmentation reactions.Comment: 19 pages, 10 figure
Variations of the ISM Compactness Across the Main Sequence of Star-Forming Galaxies: Observations and Simulations
(abridged) The majority of star-forming galaxies follow a simple empirical
correlation in the star formation rate (SFR) versus stellar mass () plane,
usually referred to as the star formation Main Sequence (MS). Here we combine a
set of hydro-dynamical simulations of interacting galactic disks with
state-of-the-art radiative transfer codes to analyze how the evolution of
mergers is reflected upon the properties of the MS. We present
\textsc{Chiburst}, a Markov Chain Monte Carlo (MCMC) Spectral Energy
Distribution (SED) code that fits the multi-wavelength, broad-band photometry
of galaxies and derives stellar masses, star formation rates, and geometrical
properties of the dust distribution. We apply this tool to the SEDs of
simulated mergers and compare the derived results with the reference output
from the simulations. Our results indicate that changes in the SEDs of mergers
as they approach coalescence and depart from the MS are related to an evolution
of dust geometry in scales larger than a few hundred parsecs. This is reflected
in a correlation between the specific star formation rate (sSFR), and the
compactness parameter , that parametrizes this geometry and hence
the evolution of dust temperature () with time. As mergers
approach coalescence, they depart from the MS and increase their compactness,
which implies that moderate outliers of the MS are consistent with late-type
mergers. By further applying our method to real observations of Luminous
Infrared Galaxies (LIRGs), we show that the merger scenario is unable to
explain these extreme outliers of the MS. Only by significantly increasing the
gas fraction in the simulations are we able to reproduce the SEDs of LIRGs.Comment: 18 pages, 10 figures, accepted in Ap
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