1,840 research outputs found
Scalar K pi form factor and light quark masses
Recent experimental improvements on K-decay data allow for a precise
extraction of the strangeness-changing scalar K pi form factor and the related
strange scalar spectral function. On the basis of this scalar as well as the
corresponding pseudoscalar spectral function, the strange quark mass is
determined to be m_s(2 GeV) = 92 +- 9 MeV. Further taking into account chiral
perturbation theory mass ratios, the light up and down quark masses turn out to
be m_u(2 GeV) = 2.7 +- 0.4 MeV as well as m_d(2 GeV) = 4.8 +- 0.5 MeV. As a
by-product, we also find a value for the Cabibbo angle |V_{us}| = 0.2236(29)
and the ratio of meson decay constants F_K/F_\pi = 1.203(16). Performing a
global average of the strange mass by including extractions from other channels
as well as lattice QCD results yields m_s(2 GeV) = 94 +- 6 MeV.Comment: 5 pages, 2 figures; comparison with lattice and global average added;
version to appear in Phys. Rev.
Precise Determination of |V{us}| from Lattice Calculations of Pseudoscalar Decay Constants
Combining the ratio of experimental kaon and pion decay widths, Gamma(K to mu
antineutrino{mu} (gamma)) / Gamma(pi to mu \antineutrino (gamma)), with a
recent lattice gauge theory calculation of f{K}/f{pi} provides a precise value
for the CKM quark mixing matrix element |V{us}|=0.2236(30) or if 3 generation
unitarity is assumed |V{us}|=0.2238(30). Comparison with other determinations
of that fundamental parameter, implications, and an outlook for future
improvements are given
Gestion des forêts feuillues en contexte méditerranéen : exemples de gestion irrégularisante, continue, multifonctionnelle et proche de la nature dans l'Aude -
Ce texte est le compte rendu d'une tournée organisée par l'association Pro Silva, en collaboration avec Forêt Méditerranéenne et la société Alcina. Cette visite s'est déroulée le samedi 19 mars 2011, sur les communes d'Arques et de St-Just-et-le-Bézu dans la région de Couiza dans l'Aude. Elle a permis aux 40 participants de confronter leurs points de vue sur la gestion continue des taillis méditerranéens, dans les contextes de moyenne montagne et de piémonts
The Triple P-Positive Parenting Program: a systematic review and meta-analysis of a multi-level system of parenting support
This systematic review and meta-analysis examined the effects of the multilevel Triple P-Positive Parenting Program system on a broad range of child, parent and family outcomes. Multiple search strategies identified 116 eligible studies conducted over a 33-year period, with 101 studies comprising 16,099 families analyzed quantitatively. Moderator analyses were conducted using structural equation modeling. Risk of bias within and across studies was assessed. Significant short-term effects were found for: children's social, emotional and behavioral outcomes (d = 0.473); parenting practices (d = 0.578); parenting satisfaction and efficacy (d = 0.519); parental adjustment (d = 0340); parental relationship (d = 0.225) and child observational data (d = 0.501). Significant effects were found for all outcomes at long-term including parent observational data (d = 0.249). Moderator analyses found that study approach, study power, Triple P level, and severity of initial child problems produced significant effects in multiple moderator models when controlling for other significant moderators. Several putative moderators did not have significant effects after controlling for other significant moderators. The positive results for each level of the Triple P system provide empirical support for a blending of universal and targeted parenting interventions to promote child, parent and family wellbeing. (C) 2014 Elsevier Ltd. All rights reserved
Virtual O(\a_s) corrections to the inclusive decay
We present in detail the calculation of the O(\a_s) virtual corrections to
the matrix element for b \to s \g. Besides the one-loop virtual corrections
of the electromagnetic and color dipole operators and , we include
the important two-loop contribution of the four-Fermi operator . By
applying the Mellin-Barnes representation to certain internal propagators, the
result of the two-loop diagrams is obtained analytically as an expansion in
. These results are then combined with existing O(\a_s)
Bremsstrahlung corrections in order to obtain the inclusive rate for B \to X_s
\g. The new contributions drastically reduce the large renormalization scale
dependence of the leading logarithmic result. Thus a very precise Standard
Model prediction for this inclusive process will become possible once also the
corrections to the Wilson coefficients are available.Comment: 29 pages, uses epsfig.sty, 12 postscript figures include
Use of dual carbon–chlorine isotope analysis to assess the degradation pathways of 1,1,1-trichloroethane in groundwater
Compound-specific isotope analysis (CSIA) is a powerful tool to track contaminant fate in groundwater. However, the application of CSIA to chlorinated ethanes has received little attention so far. These compounds are toxic and prevalent groundwater contaminants of environmental concern. The high susceptibility of chlorinated ethanes like 1,1,1-trichloroethane (1,1,1-TCA) to be transformed via different competing pathways (biotic and abiotic) complicates the assessment of their fate in the subsurface. In this study, the use of a dual C-Cl isotope approach to identify the active degradation pathways of 1,1,1- TCA is evaluated for the first time in an aerobic aquifer impacted by 1,1,1-TCA and trichloroethylene (TCE) with concentrations of up to 20 mg/L and 3.4 mg/L, respectively. The reaction-specific dual carbon-chlorine (C-Cl) isotope trends determined in a recent laboratory study illustrated the potential of a dual isotope approach to identify contaminant degradation pathways of 1,1,1-TCA. Compared to the dual isotope slopes (Δδ13C/Δδ37CI) previously determined in the laboratory for dehydrohalogenation/hydrolysis (DH/HY, 0.33 ± 0.04) and oxidation by persulfate (∞), the slope determined from field samples (0.6 ± 0.2, r2 = 0.75) is closer to the one observed for DH/HY, pointing to DH/HY as the predominant degradation pathway of 1,1,1-TCA in the aquifer. The observed deviation could be explained by a minor contribution of additional degradation processes. This result, along with the little degradation of TCE determined from isotope measurements, confirmed that 1,1,1-TCA is the main source of the 1,1-dichlorethylene (1,1-DCE) detected in the aquifer with concentrations of up to 10 mg/L. This study demonstrates that a dual C-Cl isotope approach can strongly improve the qualitative and quantitative assessment of 1,1,1-TCA degradation processes in the field
Up and down quark masses from Finite Energy QCD sum rules to five loops
The up and down quark masses are determined from an optimized QCD Finite
Energy Sum Rule (FESR) involving the correlator of axial-vector divergences, to
five loop order in Perturbative QCD (PQCD), and including leading
non-perturbative QCD and higher order quark mass corrections. This FESR is
designed to reduce considerably the systematic uncertainties arising from the
(unmeasured) hadronic resonance sector, which in this framework contributes
less than 3-4% to the quark mass. This is achieved by introducing an
integration kernel in the form of a second degree polynomial, restricted to
vanish at the peak of the two lowest lying resonances. The driving hadronic
contribution is then the pion pole, with parameters well known from experiment.
The determination is done in the framework of Contour Improved Perturbation
Theory (CIPT), which exhibits a very good convergence, leading to a remarkably
stable result in the unusually wide window , where
is the radius of the integration contour in the complex energy (squared)
plane. The results are: MeV, MeV, and Mev (at a scale Q=2 GeV).Comment: Additional references to lattice QCD results have been adde
Resumming QCD vacuum fluctuations in three-flavour Chiral Perturbation Theory
Due to its light mass of order Lambda_QCD, the strange quark can play a
special role in Chiral Symmetry Breaking (ChSB): differences in the pattern of
ChSB in the limits N_f=2 (m_u,m_d->0, m_s physical) and N_f=3 (m_u,m_d,m_s->0)
may arise due to vacuum fluctuations of s-bar s pairs, related to the violation
of the Zweig rule in the scalar sector and encoded in particular in the O(p^4)
low-energy constants L_4 and L_6. In case of large fluctuations, we show that
the customary treatment of SU(3)xSU(3) chiral expansions generate instabilities
upsetting their convergence. We develop a systematic program to cure these
instabilities by resumming nonperturbatively vacuum fluctuations of s-bar s
pairs, in order to extract information about ChSB from experimental
observations even in the presence of large fluctuations. We advocate a Bayesian
framework for treating the uncertainties due to the higher orders. As an
application, we present a three-flavour analysis of the low-energy pi-pi
scattering and show that the recent experimental data imply a lower bound on
the quark mass ratio 2m_s/(m_u+m_d) > 14 at 95 % confidence level. We outline
how additional information may be incorporated to further constrain the pattern
of ChSB in the N_f=3 chiral limit.Comment: 58 pages, 8 figure
Application of the operator product expansion to the short distance behavior of nuclear potentials
We investigate the short distance behavior of nucleon-nucleon (NN) potentials
defined through Bethe-Salpeter wave functions, by perturbatively calculating
anomalous dimensions of 6-quark operators in QCD. Thanks to the asymptotic
freedom of QCD, 1-loop computations give certain exact results for the
potentials in the zero distance limit. In particular the functional form of the
S-state central NN potential at short distance is predicted to be a little
weaker than . On the other hand, due to the intriguing character of the
anomalous dimension spectrum, perturbative considerations alone can not
determine whether this potential is repulsive or attractive at short distances.
A crude estimation suggests that the force at short distance is repulsive, as
found numerically in lattice QCD. A similar behavior is found for the tensor
potential.Comment: 40 pages, no figure
- …