770 research outputs found
Bd,s→ρ,ω,K*,ϕ decay form factors from light-cone sum rules reexamined
We present an improved calculation of B--> light vector form factors from light-cone sum rules, including one-loop radiative corrections to twist-2 and twist-3 contributions, and leading order twist-4 corrections. The total theoretical uncertainty of our results at zero momentum transfer is typically 10% and can be improved, at least in part, by reducing the uncertainty of hadronic input parameters. We present our results in a way which details the dependence of the form factors on these parameters and facilitates the incorporation of future updates of their values from, e.g., lattice calculations. We also give simple and easy-to-implement parametrizations of the q2 dependence of the form factors which are valid in the full kinematical regime of q2
Improved analysis of B → πeν from QCD sum rules on the light-cone
We present a new calculation of the Brightarrowpi form-factor f+, relevant for the measurement of |Vub| from semileptonic Brightarrowpi transitions, from QCD sum rules on the light-cone. The new element is the calculation of radiative corrections to next-to-leading twist-3 accuracy. We find that these contributions are factorizable at O(alphas), which lends additional support to the method of QCD sum rules on the light-cone. We obtain f+(0) = 0.26+/-0.06+/-0.05, where the first error accounts for the uncertainty in the input-parameters and the second is a guesstimate of the systematic uncertainty induced by the approximations inherent in the method. We also obtain a simple parametrization of the form-factor which is valid in the entire kinematical range of semileptonic decays and consistent with vector-meson dominance at large momentum-transfer
Dark matter from cosmic defects on galactic scales?
We discuss the possible dynamical role of extended cosmic defects on galactic
scales, specifically focusing on the possibility that they may provide the dark
matter suggested by the classical problem of galactic rotation curves. We
emphasize that the more standard defects (such as Goto-Nambu strings) are
unsuitable for this task, but show that more general models (such as transonic
wiggly strings) could in principle have a better chance. In any case, we show
that observational data severely restricts any such scenarios.Comment: Submitted to Phys. Rev. D (Brief Reports). v2: Reference added and
some typos corrected, matches published versio
Operator Relations for SU(3) Breaking Contributions to K and K* Distribution Amplitudes
We derive constraints on the asymmetry a1 of the momentum fractions carried
by quark and antiquark in K and K* mesons in leading twist. These constraints
follow from exact operator identities and relate a1 to SU(3) breaking
quark-antiquark-gluon matrix elements which we determine from QCD sum rules.
Comparing our results to determinations of a1 from QCD sum rules based on
correlation functions of quark currents, we find that, for a1^\parallel(K*) the
central values agree well and come with moderate errors, whereas for a1(K) and
a1^\perp(K*) the results from operator relations are consistent with those from
quark current sum rules, but come with larger uncertainties. The consistency of
results confirms that the QCD sum rule method is indeed suitable for the
calculation of a1. We conclude that the presently most accurate predictions for
a1 come from the direct determination from QCD sum rules based on correlation
functions of quark currents and are given by: a1(K) = 0.06\pm 0.03,
a1^\parallel(K*) = 0.03\pm 0.02, a1^\perp(K*) = 0.04\pm 0.03.Comment: 21 page
Discrete Matter, Far Fields, and Dark Matter
We show that in cosmology the gravitational action of the far away matter has
quite relevant effects, if retardation of the forces and discreteness of matter
(with its spatial correlation) are taken into account. The expansion rate is
found to be determined by the density of the far away matter, i.e., by the
density of matter at remote times. This leads to the introduction of an
effective density, which has to be five times larger than the present one, if
the present expansion rate is to be accounted for. The force per unit mass on a
test particle is found to be of the order of 0.2cH_0. The corresponding
contribution to the virial of the forces for a cluster of galaxies is also
discussed, and it is shown that it fits the observations if a decorrelation
property of the forces at two separated points is assumed. So it appears that
the gravitational effects of the far away matter may have the same order of
magnitude as the corresponding local effects of dark matter.Comment: 16 pages, 1 figure. LaTex documen
VV124 (UGC4879): A new transitional dwarf galaxy in the periphery of the Local Group
We present the first resolved-star photometry of VV124 (UGC4879) and find
that this is the most isolated dwarf galaxy in the periphery of the Local
Group. Based on imaging and spectroscopic follow up observations with the 6m
BTA telescope, we resolve VV124 into 1560 stars down to the limiting magnitude
levels of V~25.6 and I~23.9. The young blue stellar populations and emission
gas are found near the core, but noticeably displaced from the center of the
galaxy as traced by dominant evolved red stars. The mean radial velocity
derived from the spectra of two Blue Supergiant stars, an HII region and
unresolved continuum sources is -80+/-10 km/s. The evolved ``red tangle''
stellar populations, which contains the red giant branch (RGB), are identified
at large galactocentric radii. We use the I-band luminosity function to
determine the distance based on the Tip of RGB method, 1.1+/-0.1 Mpc. This is
~10 times closer than the values usually assumed in the literature, and we
provide revised distance dependent parameters. From the mean (V-I) color of the
RGB, we estimate the mean metallicity as [Fe/H]~-1.37 dex. Despite of its
isolated location, the properties of VV124 are clearly not those of a galaxy in
formation, but rather similar to a transitional dIrr/dSph type.Comment: 4 pages, submitted to MNRAS Letter
Gravitational lensing in braneworld gravity: formalism and applications
In this article, we develop a formalism which is different from the standard
lensing scenario and is necessary for understanding lensing by gravitational
fields which arise as solutions of the effective Einstein equations on the
brane. We obtain general expressions for measurable quantities such as time
delay, deflection angle, Einstein ring and magnification. Subsequently, we
estimate the deviations (relative to the standard lensing scenario) in the
abovementioned quantities by considering the line elements for clusters and
spiral galaxies obtained by solving the effective Einstein equations on the
brane. Our analysis reveals that gravitational lensing can be a useful tool for
testing braneworld gravity as well as the existence of extra dimensions.Comment: 20 pages, 1 figure, 2 tables. Accepted for publication in Classical
and Quantum Gravit
Gamma-ray signatures of annihilation to charged leptons in dark matter substructure
Due to their higher concentrations and small internal velocities, Milky Way
subhalos can be at least as important as the smooth halo in accounting for the
GeV positron excess via dark matter annihilation. After showing how this can be
achieved in various scenarios, including in Sommerfeld models, we demonstrate
that, in this case, the diffuse inverse-Compton emission resulting from
electrons and positrons produced in substructure leads to a nearly-isotropic
signal close to the level of the isotropic GeV gamma-ray background seen by
Fermi. Moreover, we show that HESS cosmic-ray electron measurements can be used
to constrain multi-TeV internal bremsstrahlung gamma rays arising from
annihilation to charged leptons.Comment: 8 pages, 4 figures; minor updates to match published versio
Candidate Tidal Dwarf Galaxies in the Compact Group CG J1720-67.8
This is the second part of a detailed study of the ultracompact group CG
J1720-67.8: in the first part we have focused the attention on the three main
galaxies of the group and we have identified a number of candidate tidal dwarf
galaxies (TDGs). Here we concentrate on these candidate TDGs. Absolute
photometry of these objects in BVRJHKs bands confirms their relatively blue
colors, as we already expected from the inspection of optical and near-infrared
color maps and from the presence of emission-lines in the optical spectra. The
physical conditions in such candidate TDGs are investigated through the
application of photoionization models, while the optical colors are compared
with grids of spectrophotometric evolutionary synthesis models from the
literature. Although from our data self-gravitation cannot be proved for these
objects, their general properties are consistent with those of other TDG
candidates. Additionally we present the photometry of a few ``knots'' detected
in the immediate surroundings of CG J1720-67.8 and consider the possibility
that these objects might belong to a dwarf population associated with the
compact group.Comment: Accepted for publication in the Astrophysical Journa
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