2,699 research outputs found
New Analysis of the Delta I = 1/2 Rule in Kaon Decays and the B_K Parameter
We present a new analysis of the Delta I = 1/2 rule in K --> pi pi decays and
the B_K parameter. We use the 1/N_c expansion within the effective chiral
lagrangian for pseudoscalar mesons and compute the hadronic matrix elements at
leading and next-to-leading order in the chiral and the 1/N_c expansions.
Numerically, our calculation reproduces the dominant Delta I = 1/2 K --> pi pi
amplitude. Our result depends only moderately on the choice of the cutoff scale
in the chiral loops. The Delta I = 3/2 amplitude emerges sufficiently
suppressed but shows a significant dependence on the cutoff. The B_K parameter
turns out to be smaller than the value previously obtained in the 1/N_c
approach. It also shows a significant dependence on the choice of the cutoff
scale. Our results indicate that corrections from higher order terms and/or
higher resonances are large for the Delta I = 3/2 K --> pi pi amplitude and the
(|Delta S| = 2) K^0 -- anti K^0 transition amplitude.Comment: 50 pages, LaTeX, 13 eps figure
Recommended from our members
Infrared spectroscopy of chondrites and their components: a link between meteoritics and astronomy?
Analyzing epsilon'/epsilon in the 1/N_c Expansion
We present a recent analysis of epsilon'/epsilon in the 1/N_c expansion. We
show that the 1/N_c corrections to the matrix element of Q_6 are large and
positive, indicating a Delta I=1/2 enhancement similar to the one of Q_1 and
Q_2 which dominate the CP conserving amplitude. This enhances the CP ratio and
can bring the standard model prediction close to the measured value for central
values of the parameters.Comment: One reference corrected. 5 pages, talk presented by P.H. Soldan at
the 3. International Conference on B Physics and CP Violation, Taipei,
Taiwan, December 3 - 7, 1999. Slightly expanded version of the article
submitted to the proceeding
Ultrasonic Testing of Rails Including Vertical Cracks - Numerical Modeling and Experimental Results
One of the possible reasons for the failure of rails in railway tracks is the appearance of vertical cracks in the head, neck or bottom of the rail (see Fig. 1). Therefore, it is necessary to detect such defects at an early stage when the cracks are still of smaller dimensions. For vertical cracks, results of ultrasonic pulse-echo measurements are difficult to interpret due to mode conversions at the crack and rail surfaces, respectively. For normal incidence, not only the attenuation of the primary wavefront but also new echoes due to converted wave modes can be observed in the A-scan data
Ties to the Rest: Autocratic Linkages and Regime Survival
The relationship between international linkages and the nature and survival of political regimes has gained increasing attention in recent years, but remains one that is poorly understood. In this article, we make three central contributions to our understanding of international linkage politics and autocratic regime survival. First, we introduce and develop the concept of “autocratic linkage,” and highlight its importance for understanding the international politics of autocratic survival. Second, we use event history analysis to demonstrate that autocratic linkage has a systematic effect on the duration of authoritarian regimes. Finally, we complement our quantitative analysis with a focused comparison of autocratic linkage politics in the Middle East. We show that variation in Saudi Arabian support for autocratic incumbents in the wake of the Arab Spring protests can be explained in significant part by variation in linkage relationships
Recommended from our members
Mid-infrared spectroscopy of CAI and AOA from the Allende CV3.2 chondrite
Mid-infrared spectra of bulk CAI from the CV3.2 chondrite Allende are presented and compared with astronomical spectra of cometary dust, zodiacal light,the circumstellar disk of beta Pictoris and dust around the red supergiant PR Per
On a Feasible–Infeasible Two-Population (FI-2Pop) Genetic Algorithm for Constrained Optimization: Distance Tracing and no Free Lunch
We explore data-driven methods for gaining insight into the dynamics of a two-population genetic algorithm (GA), which has been effective in tests on constrained optimization problems. We track and compare one population of feasible solutions and another population of infeasible solutions. Feasible solutions are selected and bred to improve their objective function values. Infeasible solutions are selected and bred to reduce their constraint violations. Interbreeding between populations is completely indirect, that is, only through their offspring that happen to migrate to the other population. We introduce an empirical measure of distance, and apply it between individuals and between population centroids to monitor the progress of evolution. We find that the centroids of the two populations approach each other and stabilize. This is a valuable characterization of convergence. We find the infeasible population influences, and sometimes dominates, the genetic material of the optimum solution. Since the infeasible population is not evaluated by the objective function, it is free to explore boundary regions, where the optimum is likely to be found. Roughly speaking, the No Free Lunch theorems for optimization show that all blackbox algorithms (such as Genetic Algorithms) have the same average performance over the set of all problems. As such, our algorithm would, on average, be no better than random search or any other blackbox search method. However, we provide two general theorems that give conditions that render null the No Free Lunch results for the constrained optimization problem class we study. The approach taken here thereby escapes the No Free Lunch implications, per se
- …