Upper Bounds on epsilon'/epsilon Parameters B_6^{(1/2)} and B_8^{(3/2)} from Large N QCD and other News

We demonstrate that in the large N approach developed by the authors in collaboration with Bardeen, the parameters B_6^{(1/2)} and B_8^{(3/2)} parametrizing the K\to\pi\pi matrix elements _0 and _2 of the dominant QCD and electroweak operators receive both negative O(1/N) corrections such that B_6^{(1/2)} < B_8^{(3/2)}<1 in agreement with the recent lattice results of the RBC-UKQCD collaboration. We also point out that the pattern of the size of the hadronic matrix elements of all QCD and electroweak penguin operators Q_i contributing to the K\to \pi \pi amplitudes A_0 and A_2, obtained by this lattice collaboration, provides further support to our large N approach. In particular, a very precise lattice result for the matrix element _0 implies for the corresponding parameter B_8^{(1/2)}=1.0\pm 0.2 to be compared with large N value B_8^{(1/2)}=1.1\pm 0.1. We discuss briefly the implications of these findings for the ratio epsilon'/epsilon. In fact, with the precise value for B_8^{(3/2)} from RBC-UKQCD collaboration, our upper bound on B_6^{(1/2)} implies epsilon'/epsilon in the SM roughly by a factor of two below its experimental value (16.6\pm 2.3)\times 10^{-4}. We also briefly comment on the parameter \hat B_K and the \Delta I=1/2$ rule.Comment: 19 pages, Additional section on results from other large N approaches added. References added. Conclusions unchanged. Matches the version to appear in JHE

Isospin-breaking in ε′/ε\varepsilon'/\varepsilon: Impact of η0\eta_0 at the Dawn of the 2020s

For direct CP-violation in $K\to\pi\pi$ decays, the usual isospin-breaking effects at the percent level are amplified by the dynamics behind the $\Delta I=1/2$ rule and conventionally encoded in $\Omega_{\rm IB}$ parameters. The updated prediction $\Omega_{\rm IB}^{(8)}=(15.9\pm 8.2)\times 10^{-2}$ of the Chiral Perturbation Theory for the strong isospin-breaking due to $\pi_3-\eta_8$ mixing confirms such a tendency but is quite sensitive to the theoretical input value of the low-energy constant corresponding to the flavour-singlet $\eta_0$ exchange contribution in this truncated octet scheme. We rather exploit the phenomenological $\eta_8-\eta_0$ mixing as a probe for the non-negligible flavour-singlet component of the physical $\eta$ pole to find $\Omega_{\rm IB}^{(9)}=(35\pm7)\times 10^{-2}$ in a complete nonet scheme. A large central value in the nonet scheme is thus substituted for a large uncertainty in the octet one. Including the experimental $\pi^+-\pi^0$ mass difference as the dominant electromagnetic isospin-breaking, we obtain for the effective parameter entering the ratio $\epsilon'/\epsilon$ an improved result $\hat\Omega_{\rm eff}^{(9)}=(29\pm7)\times 10^{-2}$ to be compared with $\hat\Omega_{\rm eff}^{(8)}=(17\pm9)\times 10^{-2}$ used in recent analyses of $\epsilon'/\epsilon$. Accordingly, we get a reduction from $(\epsilon'/\epsilon)_{\rm SM}^{(8)}=(17.4\pm 6.1)\times 10^{-4}$ to $(\epsilon'/\epsilon)_{\rm SM}^{(9)}=(13.9\pm 5.2)\times 10^{-4}$ and thereby an effective suppression of $(\epsilon'/\epsilon)_{\rm SM}$ by isospin-breaking corrections as large as $40\%$ relative to the recent RBC-UKQCD value.Comment: 18 pages, no figures, typos removed, additional clarifying comments and one reference added, results unchanged. Version to appear in EPJ

Mass Issues in Fundamental Interactions

Driven by the mass problem, we raise some issues of the fundamental interactions in terms of non trivial commutation relations implemented within toy theories.Comment: Based on lectures given at the 2008 European School of HE

MAY THE PRO-POOR IMPACTS OF TRADE LIBERALIZATION VANISH BECAUSE OF IMPERFECT INFORMATION ?

In this paper, we try to evaluate the change in welfare gains and their distribution due to trade liberalization when imperfect information is considered. The results of two versions of a computable general equilibrium (CGE) model, using GTAP database and representing goods as well as capital flows, are compared. In the first one, a standard world CGE approach is followed. In the second version we include risk aversion, imperfect information and production lag in the agricultural sector. After a brief description of the two versions, changes in welfare, represented by the income of two types of household (middle-low and middle-high) in three regions (Europe, United States, Rest of the World) after agricultural trade liberalization are presented. Theoretical and political consequences of the results are discussed.International Relations/Trade,

BSM Hadronic Matrix Elements for ϵ′/ϵ\epsilon'/\epsilon and K→ππK\to\pi\pi Decays in the Dual QCD Approach

We calculate for the first time all four-quark hadronic matrix elements of local operators possibly contributing to $K\to\pi\pi$ decays and in particular to the ratio $\epsilon'/\epsilon$ beyond the Standard Model (BSM). To this end we use the Dual QCD (DQCD) approach. In addition to 7 new mirror operators obtained from the SM ones by flipping the chirality, we count 13 BSM four-quark operators of a given chirality linearly independent of each other and of the aforesaid 14 operators for which hadronic matrix elements are already known. We present results in two bases for all these operators, one termed DQCD basis useful for the calculation of the hadronic matrix elements in the DQCD approach and the other called SD basis suited to the short distance renormalization group evolution above the 1~GeV scale. We demonstrate that the pattern of long distance evolution (meson evolution) matches the one of short distance evolution (quark-gluon evolution), a property which to our knowledge cannot be presently achieved in any other analytical framework. The highlights of our paper are chirally enhanced matrix elements of tensor-tensor and scalar-scalar BSM operators. They could thereby explain the emerging $\epsilon'/\epsilon$ anomaly which is strongly indicated within DQCD with some support from lattice QCD. On the other hand we do not expect the BSM operators to be relevant for the $\Delta I=1/2$ rule.Comment: 39 pages, no figures, clarifying comments added, conclusions unchanged, version to appear in JHE

Prédiction de la structure et des propriétés de pyrocarbones à partir d'une reconstruction à l'échelle atomique

National audienceNous présentons ici une approche originale permettant de construire des modèles à l'échelle atomique de matériaux nanotexturés à partir de leurs images de Microscopie Electronique en Transmission à Haute Résolution (HRTEM). Partant d'une image HRTEM filtrée à hautes et basses fréquences (a), un ensemble de descripteurs statistiques est collecté puis imposé à une synthèse d'image 3D aléatoire (b). Cette dernière est ensuite utilisée comme champ de potentiel attirant les atomes sur les franges lors d'une simulation de trempe d'un liquide de carbone par dynamique moléculaire (c). Une simulation d'image HRTEM à partir du matériau virtuel obtenu permet de valider la qualité de la reconstruction (d). Nous présentons en détail cette méthode ainsi que la structure et les propriétés mécaniques calculées pour des pyrocarbones laminaires rugueux, tels que préparés et traités thermiquement