4,098 research outputs found
Implication of the B -> rho rho data on the B -> pi pi puzzle
We point out that the B -> rho rho data have seriously constrained the
possibility of resolving the B -> pi pi puzzle from the large observed B^0 ->
pi^0 pi^0 branching ratio in the available theoretical approaches. The
next-to-leading-order (NLO) contributions from the vertex corrections, the
quark loops, and the magnetic penguin evaluated in the perturbative QCD (PQCD)
approach have saturated the experimental upper bound of the B^0 -> rho^0 rho^0
branching ratio, and do not help. The NLO PQCD predictions for the B^0 ->
rho^\mp rho^\pm and B^\pm -> rho^\pm rho^0 branching ratios are consistent with
the data. The inclusion of the NLO jet function from the soft-collinear
effective theory into the QCD-improved factorization approach, though enhancing
the B^0 -> pi^0 pi^0 branching ratio sufficiently, overshoots the bound of the
B^0 -> rho^0 rho^0 branching ratio, and deteriorates the predictions for the
B^\pm -> pi^0 K^\pm and B^0 -> pi^\mp K^\pm direct CP asymmetries.Comment: 15 pages, 1 figure, REVTeX4; title changed, version to appear in
Phys. Rev.
Active Markov Information-Theoretic Path Planning for Robotic Environmental Sensing
Recent research in multi-robot exploration and mapping has focused on
sampling environmental fields, which are typically modeled using the Gaussian
process (GP). Existing information-theoretic exploration strategies for
learning GP-based environmental field maps adopt the non-Markovian problem
structure and consequently scale poorly with the length of history of
observations. Hence, it becomes computationally impractical to use these
strategies for in situ, real-time active sampling. To ease this computational
burden, this paper presents a Markov-based approach to efficient
information-theoretic path planning for active sampling of GP-based fields. We
analyze the time complexity of solving the Markov-based path planning problem,
and demonstrate analytically that it scales better than that of deriving the
non-Markovian strategies with increasing length of planning horizon. For a
class of exploration tasks called the transect sampling task, we provide
theoretical guarantees on the active sampling performance of our Markov-based
policy, from which ideal environmental field conditions and sampling task
settings can be established to limit its performance degradation due to
violation of the Markov assumption. Empirical evaluation on real-world
temperature and plankton density field data shows that our Markov-based policy
can generally achieve active sampling performance comparable to that of the
widely-used non-Markovian greedy policies under less favorable realistic field
conditions and task settings while enjoying significant computational gain over
them.Comment: 10th International Conference on Autonomous Agents and Multiagent
Systems (AAMAS 2011), Extended version with proofs, 11 page
Branching ratios and direct CP asymmetries in decays
We propose a theoretical framework for analyzing two-body nonleptonic
meson decays, based on the factorization of short-distance (long-distance)
dynamics into Wilson coefficients (hadronic matrix elements of four-fermion
operators). The parametrization of hadronic matrix elements in terms of several
nonperturbative quantities is demonstrated for the decays,
denoting a pseudoscalar meson. We consider the evolution of Wilson coefficients
with energy release in individual decay modes, and the Glauber strong phase
associated with the pion in nonfactorizable annihilation amplitudes, that is
attributed to the unique role of the pion as a Nambu-Goldstone boson and a
quark-anti-quark bound state simultaneously. The above inputs improve the
global fit to the branching ratios involving the meson, and resolves
the long-standing puzzle from the and
branching ratios, respectively. Combining short-distance dynamics associated
with penguin operators and the hadronic parameters determined from the global
fit to branching ratios, we predict direct CP asymmetries, to which the quark
loops and the scalar penguin annihilation give dominant contributions. In
particular, we predict , lower than the LHCb and CDF data.Comment: 17 pages, 3 figures, matches published versio
Proof of the Double Bubble Conjecture in R^n
The least-area hypersurface enclosing and separating two given volumes in R^n
is the standard double bubble.Comment: 20 pages, 22 figure
A tool for metadata analysis
We describe a Web-based metadata quality tool that provides statistical descriptions and visualisations of Dublin Core metadata harvested via the OAI protocol. The lightweight nature of development allows it to be used to gather contextualized requirements and some initial user feedback is discussed
Are systematic reviews up-to-date at the time of publication?
BACKGROUND: Systematic reviews provide a synthesis of evidence for practitioners, for clinical practice guideline developers, and for those designing and justifying primary research. Having an up-to-date and comprehensive review is therefore important. Our main objective was to determine the recency of systematic reviews at the time of their publication, as measured by the time from last search date to publication. We also wanted to study the time from search date to acceptance, and from acceptance to publication, and measure the proportion of systematic reviews with recorded information on search dates and information sources in the abstract and full text of the review. METHODS: A descriptive analysis of published systematic reviews indexed in Medline in 2009, 2010 and 2011 by three reviewers, independently extracting data. RESULTS: Of the 300 systematic reviews included, 271 (90%) provided the date of search in the full-text article, but only 141 (47%) stated this in the abstract. The median (standard error; minimum to maximum) survival time from last search to acceptance was 5.1 (0.58; 0 to 43.8) months (95% confidence interval = 3.9 to 6.2) and from last search to first publication time was 8.0 (0.35; 0 to 46.7) months (95% confidence interval = 7.3 to 8.7), respectively. Of the 300 reviews, 295 (98%) stated which databases had been searched, but only 181 (60%) stated the databases in the abstract. Most researchers searched three (35%) or four (21%) databases. The top-three most used databases were MEDLINE (79%), Cochrane library (76%), and EMBASE (64%). CONCLUSIONS: Being able to identify comprehensive, up-to-date reviews is important to clinicians, guideline groups, and those designing clinical trials. This study demonstrates that some reviews have a considerable delay between search and publication, but only 47% of systematic review abstracts stated the last search date and 60% stated the databases that had been searched. Improvements in the quality of abstracts of systematic reviews and ways to shorten the review and revision processes to make review publication more rapid are needed
Cooper pair islanding model of insulating nanohoneycomb films
We first review evidence for the Cooper pair insulator (CPI) phase in
amorphous nanohoneycomb (NHC) films. We then extend our analysis of
superconducting islands induced by film thickness variations in NHC films to
examine the evolution of island sizes through the magnetic field-driven SIT.
Finally, using the islanding picture, we present a plausible model for the
appearance and behavior of the CPI phase in amorphous NHC films.Comment: 7 pages, 3 figure
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