6,800 research outputs found
New ways to explore factorization in b decays
We propose to study factorization breaking effects in exclusive b decays
where they are strongly enhanced over the factorizing contributions. This can
be done by selecting final-state mesons with a small decay constant or with
spin greater than one. We find a variety of decay modes which could help
understand the dynamical origin of factorization and the mechanisms responsible
for its breaking.Comment: 30 pages, 5 figures, references added, signs corrected in eqs.
10-13,19,2
A Theoretical Reappraisal of Branching Ratios and CP Asymmetries in the Decays and Determination of the CKM Parameters
We present a theoretical reappraisal of the branching ratios and CP
asymmetries for the decays , with , taking
into account current theoretical uncertainties in the description of the
inclusive decay amplitudes from the long-distance contributions, an improved
treatment of the renormalization scale dependence, and other parametric
dependencies. Concentrating on the partial branching ratios , integrated over the invariant dilepton mass region , we calculate theoretical precision on the
charge-conjugate averaged partial branching ratios , CP asymmetries in partial decay rates
, and the ratio of the
branching ratios .
For the central values of the CKM parameters, we find , , , , and . The dependence of and on the CKM parameters is worked out and the resulting constraints on
the unitarity triangle from an eventual measurement of are
illustrated.Comment: 18 pages, 7 figures (require epsf.sty
Rare b hadron decays at the LHC
With the completion of Run~I of the CERN Large Hadron Collider, particle
physics has entered a new era. The production of unprecedented numbers of
heavy-flavoured hadrons in high energy proton-proton collisions allows detailed
studies of flavour-changing processes. The increasingly precise measurements
allow to probe the Standard Model with a new level of accuracy. Rare hadron
decays provide some of the most promising approaches for such tests, since
there are several observables which can be cleanly interpreted from a
theoretical viewpoint. In this article, the status and prospects in this field
are reviewed, with a focus on precision measurements and null tests.Comment: Invited review for Annual Reviews of Nuclear and Particle Physics. v2
as publishe
Biotic indicators of carabid species richness on organically and conventionally managed arable fields
Carabids, a species rich arthropod family, potentially contribute much to biodiversity in agroecosystems, but assessing and monitoring carabid diversity is costly and time consuming. Therefore, this study aimed at finding more easily measurable parameters indicating high carabid diversity within organic and conventional management systems. Cover and number of weed species as well as activity density of single carabid species and of total carabids were investigated as potential indicators of carabid species richness. The study was carried out near Reckenfeld in Westphalia on sandy Plaggenesch soils. Three organically and four conventionally managed fields (cereals and corn) were investigated at the field margins and in the field centres from April to August 1999. Additionally, data of carabid catches and weed flora in winter cereals from an extended study in Düren (Northrhine-Westphalia) were reanalysed to validate the results. However, neither of the potential indicators showed consistently significant positive correlation with carabid diversity. This is partly attributed to the low variability of management conditions within the management systems in the studies presented
decays in and beyond the Standard Model
We briefly review the status of rare radiative and semileptonic , () decays. We discuss possible signatures
of new physics in these modes and emphazise the role of the exclusive channels.
In particular, measurements of the Forward-Backward asymmetry in decays and its zero provide a clean test of the Standard Model,
complementary to studies in decays. Further, the
Forward-Backward CP asymmetry in decays is sensitive
to possible non-standard sources of CP violation mediated by flavor changing
neutral current -penguins.Comment: Invited Talk at 7th Conference on the Intersections of Particle and
Nuclear Physics, Quebec City, Quebec, Canada, May 22-28, 200
Evaluating Poverty Impacts of Bottom-of-the-Pyramid Irrigation Technology Supply: IDE’s Rolling Baseline Approach to Household Income Impact Assessment
Time-delayed feedback in neurosystems
The influence of time delay in systems of two coupled excitable neurons is
studied in the framework of the FitzHugh-Nagumo model. Time-delay can occur in
the coupling between neurons or in a self-feedback loop. The stochastic
synchronization of instantaneously coupled neurons under the influence of white
noise can be deliberately controlled by local time-delayed feedback. By
appropriate choice of the delay time synchronization can be either enhanced or
suppressed. In delay-coupled neurons, antiphase oscillations can be induced for
sufficiently large delay and coupling strength. The additional application of
time-delayed self-feedback leads to complex scenarios of synchronized in-phase
or antiphase oscillations, bursting patterns, or amplitude death.Comment: 13 pages, 13 figure
Is 10% Good Enough? Cooperative Extension Work in Indian Country
The Cooperative Extension system delivers local programs in virtually all of America\u27s counties. Extension\u27s intergovernmental model capitalizes on resources of counties, states, and the federal government and provides an institutional framework for county Extension work. The Extension system and model is not as applicable, however, for members of America\u27s 562 Indian tribes, particularly those living on 314 major Indian reservations. This 90 year-old template is woefully inadequate for Indian Country Extension work. This article presents background on how this situation evolved and suggests that national-scale dialogue to develop program equity for this underserved and place-bound audience is needed
A Comparative Study of the Decays in Standard Model and Supersymmetric Theories
Using improved theoretical calculations of the decay form factors in the
Light Cone-QCD sum rule approach, we investigate the decay rates, dilepton
invariant mass spectra and the forward-backward (FB) asymmetry in the decays () in the standard
model (SM) and a number of popular variants of the supersymmetric (SUSY)
models. Theoretical precision on the differential decay rates and FB-asymmetry
is estimated in these theories taking into account various parametric
uncertainties. We show that existing data on and the
experimental upper limit on the branching ratio provide interesting bounds on the coefficients of the underlying
effective theory. We argue that the FB-asymmetry in
constitutes a precision test of the SM and its measurement in forthcoming
experiments may reveal new physics. In particular, the presently allowed
large- solutions in SUGRA models, as well as more general
flavor-violating SUSY models, yield FB-asymmetries which are characteristically
different from the corresponding ones in the SM.Comment: 36 pages, 12 figures (require epsfig.sty), 8 Tables, LaTeX2e;
subsection 6.4 corrected, minor changes in numerical results, Figures 3 and 9
to 12 modified; submitted to Physical Review
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