94 research outputs found
Constraining Form Factors with the Method of Unitarity Bounds
The availability of a reliable bound on an integral involving the square of
the modulus of a form factor on the unitarity cut allows one to constrain the
form factor at points inside the analyticity domain and its shape parameters,
and also to isolate domains on the real axis and in the complex energy plane
where zeros are excluded. In this lecture note, we review the mathematical
techniques of this formalism in its standard form, known as the method of
unitarity bounds, and recent developments which allow us to include information
on the phase and modulus along a part of the unitarity cut. We also provide a
brief summary of some results that we have obtained in the recent past, which
demonstrate the usefulness of the method for precision predictions on the form
factors.Comment: 12 pages, 2 figures; Lecture given at the DAE-BRNS Workshop on Hadron
Physics, Bhabha Atomic Research Centre, Mumbai, India, October 31-November 4,
2011, submitted to Proceeding
Semileptonic charm decays D \to \pi l \nu_{\l} and from QCD Light-Cone Sum Rules
We present a new calculation of the and form factors from
QCD light-cone sum rules. The scheme for the -quark mass is
used and the input parameters are updated. The results are , and
. Combining the calculated form
factors with the latest CLEO data, we obtain and
where the first and second errors are of experimental origin and the third
error is due to the estimated uncertainties of our calculation. We also
evaluate the form factors and and predict the slope
parameters at . Furthermore, calculating the form factors from the sum
rules at , we fit them to various parameterizations. After analytic
continuation, the shape of the form factors in the whole
semileptonic region is reproduced, in a good agreement with experiment.Comment: 34 pages, 5 figure
Revegetation of Fluvial Mine Tailing Deposits: The Use of Five Riparian Shrub Species
Fluvial deposition of mine tailings has caused extensive damage to riparian ecosystems throughout the West. Willows are often used for revegetation of fluvial mine tailing deposits but some species accumulate toxic concentrations of metals in leaves and stems. A greenhouse experiment was conducted to determine the value of thinleaf alder [Alnus incana (L.) Moench spp. tinuifolia (Nutt.) Breitung], water birch (Betula occidentalis Hook.), red osier dogwood (Cornus sericea L. spp. sericea), and shrubby cinquefoil [Dasiphora fruticosa (L.) Rybd.] compared to Geyer willow (Salix geyeriana Andersson) for revegetation of fluvial tailing deposits along the Upper Arkansas River. Bare root shrubs were grown in tailings amended with lime and composted biosolids. Tailings were collected from three acidic and metal contaminated deposits along the Arkansas River south of Leadville, Colorado. All shrubs survived the two month experiment. Averaged across source deposits, total biomass during the experiment increased for alder, birch, dogwood, cinquefoil, and willow by 831, 689, 579, 525, and 683%, respectively. All species concentrated Pb and Zn belowground. Dogwood assimilated little Zn (44.0 mg kg-1) into its leaves and stems, but showed signs of nutrient deficiency which could have been induced by metal stress. Alder and cinquefoil partitioned Pb aboveground, 30.3 and 26.1 mg kg-1, respectively, which is unusual, but concentrations were below toxicity thresholds for humans and animals. All species evaluated did not exhibit greater growth when compared to Geyer willow, but the other four riparian species had metal partitioning characteristics valuable for managers planning for in situ restoration of mine tailing deposits
Spectral density in resonance region and analytic confinement
We study the role of finite widths of resonances in a nonlocal version of the
Wick-Cutkosky model. The spectrum of bound states is known analytically in this
model and forms linear Regge tragectories. We compute the widths of resonances,
calculate the spectral density in an extension of the Breit-Wigner {\it ansatz}
and discuss a mechanism for the damping of unphysical exponential growth of
observables at high energy due to finite widths of resonances.Comment: 13 pages, RevTeX, 6 figures. Revised version with typographical
corrections and additional comments in conclusion
Relativistic Restrictions on the Distinguishability of Orthogonal Quantum States
We analyze the restrictions on the distinguishability of quantum states
imposed by special relativity. An explicit expression relating the error
probability for distinguishing between two orthogonal single-photon states with
the time elapsed from the start of the measurement procedure until the
measurement result is obtained by the observer.Comment: 9 pages, 1 figure (misprints in formulas corrected
Model-Independent Semileptonic Form Factors Using Dispersion Relations
We present a method for parametrizing heavy meson semileptonic form factors
using dispersion relations, and from it produce a two-parameter description of
the B -> B elastic form factor. We use heavy quark symmetry to relate this
function to B -> D* l nu form factors, and extract
|V_cb|=0.0355^{+0.0029}_{-0.0025} from experimental data with a least squares
fit. Our method eliminates model-dependent uncertainties inherent in choosing a
parametrization for the extrapolation of the differential decay rate to
threshold.Comment: uses lanlmac(harvmac) and epsf, 12 pages, 1 eps figure included (Talk
by BG at the 6-th International Symposium on Heavy Flavour Physics, Pisa,
Italy, 6--10 June, 1995
Unitarity Constraints on the B and B^* Form Factors from QCD Analyticity and Heavy Meson Spin Symmetry
A method of deriving bounds on the weak meson form factors, based on
perturbative QCD, analyticity and unitarity, is generalized in order to fully
exploit heavy quark spin symmetry in the ground state doublet of
pseudoscalar and vector mesons. All the relevant form factors of
these mesons are taken into account in the unitarity sum. They are treated as
independent functions along the timelike axis, being related by spin symmetry
only near the zero recoil point. Heavy quark vacuum polarisation up to three
loops in perturbative QCD and the experimental cross sections are used as input. We obtain bounds on the charge radius
of the elastic form factor of the meson, which considerably improve
previous results derived in the same framework.Comment: 13 pages LaTex, 1 figure as a separate ps fil
Towards a Generalized Distribution Formalism for Gauge Quantum Fields
We prove that the distributions defined on the Gelfand-Shilov spaces, and
hence more singular than hyperfunctions, retain the angular localizability
property. Specifically, they have uniquely determined support cones. This
result enables one to develop a distribution-theoretic techniques suitable for
the consistent treatment of quantum fields with arbitrarily singular
ultraviolet and infrared behavior. The proofs covering the most general case
are based on the use of the theory of plurisubharmonic functions and
Hormander's estimates.Comment: 12 p., Department of Theoretical Physics, P.N.Lebedev Physical
Institute, Leninsky prosp. 53, Moscow 117924, Russi
New Constraints on Dispersive Form Factor Parameterizations from the Timelike Region
We generalize a recent model-independent form factor parameterization derived
from rigorous dispersion relations to include constraints from data in the
timelike region. These constraints dictate the convergence properties of the
parameterization and appear as sum rules on the parameters. We further develop
a new parameterization that takes into account finiteness and asymptotic
conditions on the form factor, and use it to fit to the elastic \pi
electromagnetic form factor. We find that the existing world sample of timelike
data gives only loose bounds on the form factor in the spacelike region, but
explain how the acquisition of additional timelike data or fits to other form
factors are expected to give much better results. The same parameterization is
seen to fit spacelike data extremely well.Comment: 24 pages, latex (revtex), 3 eps figure
Dispersive Bounds on The Shape Of Lambda_b to Lambda_c l {\bar \nu_l} Formfactors
We derive a theoretically allowed domain for the charge radius and
curvature of the Isgur-Wise function describing the decay . Our method uses crossing symmetry, dispersion
relations and analyticity in the context of the Heavy Quark Effective Theory
but is independent of the specifics of any given model. The experimentally
determined values of the masses have been used as input information.
The results are of interest for testing different models employed to calculate
the heavy baryon formfactors which are used for the extraction of
from the experimental data.Comment: 18 pages, 1 figure included via psfi
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