1,817 research outputs found
Two-body hadronic charmed meson decays
We study in this work the two-body hadronic charmed meson decays, including
both the PP and VP modes. The latest experimental data are first analyzed in
the diagrammatic approach. The magnitudes and strong phases of the flavor
amplitudes are extracted from the Cabibbo-favored (CF) decay modes using
minimization. The best-fitted values are then used to predict the
branching fractions of the singly-Cabibbo-suppressed (SCS) and
doubly-Cabibbo-suppressed decay modes in the flavor SU(3) symmetry limit. We
observe significant SU(3) breaking effects in some of SCS channels. In the case
of VP modes, we point out that the and amplitudes cannot be
completely determined based on currently available data. We conjecture that the
quoted experimental results for both and are overestimated. We compare the sizes of color-allowed and
color-suppressed tree amplitudes extracted from the diagrammatical approach
with the effective parameters and defined in the factorization
approach. The ratio is more or less universal among the , and modes. This feature allows
us to discriminate between different solutions of topological amplitudes. For
the long-standing puzzle about the ratio , we argue that, in addition to the SU(3)
breaking effect in the spectator amplitudes, the long-distance resonant
contribution through the nearby resonance can naturally explain why
decays more copiously to than through the
-exchange topology.Comment: 32 pages, 5 figures. An alternative method for error bar extraction
is used; last columns of Tables~I to VI, and all entries in Tables~VII, VIII
and X are modified. To appear in PRD
A-dependence of hadronization in nuclei
The A-dependence of models for the attenuation of hadron production in
semi-inclusive deep-inelastic scattering on a nucleus is investigated for
realistic matter distributions. It is shown that the dependence for a pure
partonic (absorption) mechanism is more complicated than a simple
() behavior, commonly found when using rectangular or Gaussian
distributions, but that the A-dependence may still be indicative for the
dominant mechanism of hadronization.Comment: 4 pages, 4 figure
Conceptualizing new forms of volunteering in urban governance
This article argues that developments in the spheres of the state, the market, and the community have changed their boundaries, affecting volunteering in urban governance. Shifts in the division of tasks between the state and community have led to a new form of manufactured volunteering, while technological developments have made it easier to bridge trust gaps, resulting in platform volunteering. Moreover, business organizations pursuing public goals and using public resources have created a new form of economic volunteering. Thus, three illustrative cases are used to explore these new forms of volunteering and their main strengths and weaknesses. These new forms challenge traditional conceptions of volunteering work and the ideal-typical role model of “the volunteer.”</p
Testing the Hypothesis of Modified Dynamics with Low Surface Brightness Galaxies and Other Evidence
The rotation curves of low surface brightness galaxies provide a unique data
set with which to test alternative theories of gravitation over a large dynamic
range in size, mass, surface density, and acceleration. Many clearly fail,
including any in which the mass discrepancy appears at a particular
length-scale. One hypothesis, MOND [Milgrom 1983, ApJ, 270, 371], is consistent
with the data. Indeed, it accurately predicts the observed behavior. We find no
evidence on any scale which clearly contradicts MOND, and a good deal which
supports it.Comment: Accepted for publication in the Astrophysical Journal. 35 pages
AAStex + 9 figures. This result surprised the bejeepers out of us, to
Halpha rotation curves: the soft core question
We present high resolution Halpha rotation curves of 4 late-type dwarf
galaxies and 2 low surface brightness galaxies (LSB) for which accurate HI
rotation curves are available from the literature. Observations are carried out
at Telescopio Nazionale Galileo (TNG). For LSB F583-1 an innovative dispersing
element was used, the Volume Phase Holographic (VPH) with a dispersion of about
0.35 A/pxl. We find good agreement between the Halpha data and the HI
observations and conclude that the HI data for these galaxies suffer very
little from beam smearing. We show that the optical rotation curves of these
dark matter dominated galaxies are best fitted by the Burkert profile. In the
centers of galaxies, where the N-body simulations predict cuspy cores and fast
rising rotation curves, our data seem to be in better agreement with the
presence of soft cores.Comment: Accepted for Publication in ApJ with minor changes require
Resolving the Formation of Protogalaxies. III. Feedback from the First Stars
The first stars form in dark matter halos of masses ~10^6 M_sun as suggested
by an increasing number of numerical simulations. Radiation feedback from these
stars expels most of the gas from their shallow potential well of their
surrounding dark matter halos. We use cosmological adaptive mesh refinement
simulations that include self-consistent Population III star formation and
feedback to examine the properties of assembling early dwarf galaxies. Accurate
radiative transport is modeled with adaptive ray tracing. We include supernova
explosions and follow the metal enrichment of the intergalactic medium. The
calculations focus on the formation of several dwarf galaxies and their
progenitors. In these halos, baryon fractions in 10^8 solar mass halos decrease
by a factor of 2 with stellar feedback and by a factor of 3 with supernova
explosions. We find that radiation feedback and supernova explosions increase
gaseous spin parameters up to a factor of 4 and vary with time. Stellar
feedback, supernova explosions, and H_2 cooling create a complex, multi-phase
interstellar medium whose densities and temperatures can span up to 6 orders of
magnitude at a given radius. The pair-instability supernovae of Population III
stars alone enrich the halos with virial temperatures of 10^4 K to
approximately 10^{-3} of solar metallicity. We find that 40% of the heavy
elements resides in the intergalactic medium (IGM) at the end of our
calculations. The highest metallicity gas exists in supernova remnants and very
dilute regions of the IGM.Comment: 15 pages, 16 figures, accepted to ApJ. Many changes, including
estimates of metal line cooling. High resolution images and movies available
at http://www.slac.stanford.edu/~jwise/research/PGalaxies3
Smooth HI Low Column Density Outskirts In Nearby Galaxies
This is an author-created, un-copyedited version of an article published in The Astronomical Journal. The Version of Record is available online at https://doi.org/10.3847/1538-3881/aabbaa.The low column density gas at the outskirts of galaxies as traced by the 21 cm hydrogen line emission (H i) represents the interface between galaxies and the intergalactic medium, i.e., where galaxies are believed to get their supply of gas to fuel future episodes of star formation. Photoionization models predict a break in the radial profiles of H i at a column density of ∼5 × 10 19 cm -2 due to the lack of self-shielding against extragalactic ionizing photons. To investigate the prevalence of such breaks in galactic disks and to characterize what determines the potential edge of the H i disks, we study the azimuthally averaged H i column density profiles of 17 nearby galaxies from the H i Nearby Galaxy Survey and supplemented in two cases with published Hydrogen Accretion in LOcal GAlaxieS data. To detect potential faint H i emission that would otherwise be undetected using conventional moment map analysis, we line up individual profiles to the same reference velocity and average them azimuthally to derive stacked radial profiles. To do so, we use model velocity fields created from a simple extrapolation of the rotation curves to align the profiles in velocity at radii beyond the extent probed with the sensitivity of traditional integrated H i maps. With this method, we improve our sensitivity to outer-disk H i emission by up to an order of magnitude. Except for a few disturbed galaxies, none show evidence of a sudden change in the slope of the H i radial profiles: the alleged signature of ionization by the extragalactic background.Peer reviewedFinal Accepted Versio
Calculation of 1/m^3 terms in the total semileptonic width of D mesons.
We calculate the 1/ corrections in the inclusive semileptonic widths
of mesons. We show that these are due to the novel penguin type operators
that appear at this level in the transition operator. Taking into account the
nonperturbative corrections leads to the predicted value of the semileptonic
width significantly lower than the experimental value. The worsen the
situation or at the very least, within uncertainty, give small contribution. We
indicate possible ways out. It seems most probable that violations of duality
are noticeable in the energy range characteristic to the inclusive decays in
the charm family. Theoretically these deviations are related to divergence of
the high-order terms in the power expansion in the inverse heavy quark mass.Comment: Final version accepted for publication in Physical Review D (19
pages, 5 figures appended as two PS files at the end of the LATEX file
Validity of the distorted-wave impulse-approximation description of CaK data using only ingredients from a nonlocal dispersive optical model
The nonlocal implementation of the dispersive optical model (DOM) provides
all the ingredients for distorted-wave impulse-approximation (DWIA)
calculations of the reaction. It provides both the overlap function,
including its normalization, and the outgoing proton distorted wave. This
framework is applied to describe the knockout of a proton from the
and orbitals in Ca
with fixed normalizations of 0.71 and 0.60, respectively. Data were obtained in
parallel kinematics for three outgoing proton energies: 70, 100, and 135 MeV.
Agreement with the data is as good as, or better than, previous descriptions
employing local optical potentials and overlap functions from Woods-Saxon
potentials - both with standard nonlocality corrections - whose normalization
(spectroscopic factor) and radius were fitted to the data. The present analysis
suggests that slightly larger spectroscopic factors are obtained when nonlocal
optical potentials are employed than those generated with local potentials. The
results further suggest that the chosen kinematical window around 100 MeV
proton energy provides the best and cleanest method to employ the DWIA for the
analysis of this reaction. The conclusion that substantial ground-state
correlations cannot be ignored when describing a closed-shell atomic nucleus is
therefore confirmed in detail. To reach these conclusions, it is essential to
have a complete description of the nucleon single-particle propagator that
accounts for all elastic nucleon-scattering observables in a wide energy domain
up to 200 MeV. The current nonlocal implementation of the DOM fulfills this
requirement.Comment: 15 pages, 11 figure
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