1,351 research outputs found
Stringent constraints on the scalar K pi form factor from analyticity, unitarity and low-energy theorems
We investigate the scalar K pi form factor at low energies by the method of
unitarity bounds adapted so as to include information on the phase and modulus
along the elastic region of the unitarity cut. Using at input the values of the
form factor at t=0 and the Callan-Treiman point, we obtain stringent
constraints on the slope and curvature parameters of the Taylor expansion at
the origin. Also, we predict a quite narrow range for the higher order ChPT
corrections at the second Callan-Treiman point.Comment: 5 pages latex, uses EPJ style files, 3 figures, replaced with version
accepted by EPJ
Impact of on the New Physics search in decay
We discuss the uncertainty related to the amount of unwanted events in the sample of .
Those events can increase the measured differential decay rate by up to 10% in
the low region, and can be a source of non-negligible uncertainty in the
full angular distribution of the decay.
Although the transverse asymmetries should be unaffected by the presence of the
-wave pairs, coming from the scalar meson, we show that in
practice their normalization might be sensitive to those events and could
entail a sizable uncertainty in transverse asymmetries around .
For other 's that error is under about 10%.Comment: 16 pages [as published in NPB
Experimental characterization of mechanical properties of the cement-aggregate interface in concrete
International audienceThe microstructure of the Interfacial Transition Zone (ITZ) between the aggregates and the cement paste is characterized by a higher porosity than that of the bulk paste. The particular properties of this zone strongly influence the mechanical behavior of concrete. Microscopic cracks, which develop during subsequent loading, appear either in the matrix (cement paste or mortar) or along the cement-aggregates interface. Cracks could be caused by either tensile, shear strengths or by combinations of both. In this work, the mechanical properties of the cement paste – aggregate sample are experimentally studied. The experimental tests are performed on parallelepipedic samples at classical aggregate scale (one centimeter sections). These samples are composed of limestone aggregates and Portland cement paste, hereafter named ''composite ". The cement paste is prepared with a water/cement ratio of 0.5. The shape of the prepared composites makes them convenient for direct tensile and shear tests. At different stages of hydration, we performed direct tensile and shear tests on the composites by means of specific devices. The same tests were carried out on the cement paste in order to compare with the composite results. The analysis of the experimental results showed that the tensile strength of the cement-aggregate interface was about 30% lower than that of the cement paste tensile strength. Also, the shear strength of the cement-aggregate interface was smaller than the shear strength of the cement paste. In the same way as macroscopic Mohr–Coulomb criterion, we observed an increase of shear strength when normal stress increased. It provides access to a local cohesion (c) and a local friction angle ðUÞ at classical aggregate scale
Étude statistique de la réponse mécanique lors d'essais de traction directe à l'échelle locale
National audienceLa dispersion de la réponse mécanique d'un essai de traction directe sur une pâte de ciment à l'échelle locale, ou échelle de l'interface pâte de ciment/granulat, dépend, d'une part, de la dispersion des caractéristiques mécaniques de la pâte de ciment et, d'autre part, du dispositif expérimental. Une étude statistique numérique quantifie la dépendance de la dispersion des réponses mécaniques d'un essai de traction directe à la position de fixations en acier servant à la traction de l'échantillon. Les résultats de cette étude sont comparés à des observations expérimentales
Étude statistique de la réponse mécanique lors d’essais de traction directe à l’échelle locale
National audienc
Étude statistique de la réponse mécanique lors d'essais de traction directe à l'échelle locale
National audienceLa modélisation de la fissuration du béton nécessite de considérer la liaison entre la pâte de ciment et les granulats du béton, communément appelée interface, auréole de transition. Ce constat a motivé la mise en place d'essais mécaniques spécifiques en laboratoire à l'échelle dite locale afin de caractériser et d'identifier le comportement mécanique d'une pâte de ciment pure et de l'interface pâte de ciment/granulat à partir d'un échantillon composite. Des essais de traction directe sur des éprouvettes de ciment ont été mis en place dans le but d'identifier le comportement mécanique à la rupture de la pâte de ciment pure à l'échelle locale. Pour un type de ciment donné, la dispersion de la réponse mécanique des essais dépend, d'une part, de la dispersion des caractéristiques mécaniques de l'échantillon et, d'autre part, du dispositif expérimental. Cet article s'intéresse à la dispersion de la réponse mécanique sur plusieurs essais qui est grandement influencée par la préparation des échantillons. Une étude statistique numérique met en exergue la forte dépendance de la statistique des réponses mécaniques de l'essai de traction à la position des fixations en acier servant à la traction de l'échantillon. Les résultats de cette étude sont comparés à des observations expérimentales
B-->pi and B-->K transitions in standard and quenched chiral perturbation theory
We study the effects of chiral logs on the heavy-->light pseudoscalar meson
transition form factors by using standard and quenched chiral perturbation
theory combined with the static heavy quark limit. The resulting expressions
are used to indicate the size of uncertainties due to the use of the quenched
approximation in the current lattice studies. They may also be used to assess
the size of systematic uncertainties induced by missing chiral log terms in
extrapolating toward the physical pion mass. We also provide the coefficient
multiplying the quenched chiral log, which may be useful if the quenched
lattice studies are performed with very light mesons.Comment: 33 pages, 8 PostScript figures, version to appear in PR
Couplings of light I=0 scalar mesons to simple operators in the complex plane
The flavour and glue structure of the light scalar mesons in QCD are probed
by studying the couplings of the I=0 mesons and to the
operators , and to two photons. The Roy dispersive
representation for the amplitude is used to determine the
pole positions as well as the residues in the complex plane. On the real axis,
is constrained to solve the Roy equation together with elastic
unitarity up to the K\Kbar threshold leading to an improved description of
the . The problem of using a two-particle threshold as a matching
point is discussed. A simple relation is established between the coupling of a
scalar meson to an operator and the value of the related pion form-factor
computed at the resonance pole. Pion scalar form-factors as well as two-photon
partial-wave amplitudes are expressed as coupled-channel Omn\`es dispersive
representations. Subtraction constants are constrained by chiral symmetry and
experimental data. Comparison of our results for the couplings with
earlier determinations of the analogous couplings of the lightest I=1 and
scalar mesons are compatible with an assignment of the ,
, , into a nonet. Concerning the gluonic operator
we find a significant coupling to both the and the
.Comment: 31 pages, 5 figure
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