Showing papers by "Johan Bijnens published in 2003"

$K_{\ell3}$ decays in Chiral Perturbation Theory

Abstract: The process $K_{\ell3}$ is calculated to two-loop order ($p^6$) in Chiral Perturbation Theory (ChPT) in the isospin conserved case. We present expressions suitable for use with previous work in two-loop CHPT where the order $p^4$ parameters ($L_i^r$) were determined from experiment. We point out that all the order $p^6$ parameters ($C_i^r$) that appear in the value of $f_+(0)$ relevant for the determination of $|V_{us}|$ can be determined from $K_{\ell3}$ measurements via the slope and the curvature of the scalar form-factor. As a by product we update the value of the CKM matrix element $| V_{us} |$.

QCD short distance constraints and hadronic approximations

Abstract: This paper discusses a general class of ladder resummation inspired hadronic approximations. It is found that this approach naturally reproduces many successes of single meson per channel saturation models (e.g. VMD) and NJL based models. In particular the existence of a constituent quark mass and a gap equation follows naturally. We construct an approximation that satisfies a large set of QCD short-distance and large N-c constraints and reproduces many hadronic observables. We show how there exists in general a problem between QCD short-distance constraints for Green Functions and those for form factors and cross-sections following from the quark-counting rule. This problem while expected for Green functions that do not vanish in purely perturbative QCD also persists for many Green functions that are order parameters. (Less)

Scalar form factors in SU(3) chiral perturbation theory

Abstract: The scalar form factors for the pions and kaons are calculated in SU(3) Chiral Perturbation Theory at order p(6), in the isospin limit m(u)=m(d)=(m) over cap. We find in general sizable corrections of O(p(6)). We use our results to obtain information on the 1/N-c suppressed low energy constants L-4(r) and L-6(r) as well as on two O(p(6)) low energy constants. We present some numerical results for masses and decay constants as well. We derive a relation for the scalar form factors analogous to Sirlin's relation for vector form factors.

QCD Short-distance Constraints and Hadronic Approximations

Abstract: This paper discusses a general class of ladder resummation inspired hadronic approximations. It is found that this approach naturally reproduces many successes of single meson per channel saturation models (e.g. VMD) and NJL based models. In particular the existence of a constituent quark mass and a gap equation follows naturally. We construct an approximation that satisfies a large set of QCD short-distance and large $N_c$ constraints and reproduces many hadronic observables. We show how there exists in general a problem between QCD short-distance constraints for Green Functions and those for form factors and cross-sections following from the quark-counting rule. This problem while expected for Green functions that do not vanish in purely perturbative QCD also persists for many Green functions that are order parameters.

Scalar Form Factors in SU(3) Chiral Perturbation Theory

Abstract: The scalar form factors for the pions and kaons are calculated in SU(3) Chiral Perturbation Theory at order $p^6$, in the isospin limit $m_u=m_d=\hat{m}$. We find in general sizable corrections of $\mathcal{O}(p^6)$. We use our results to obtain results on the $1/N_c$ suppressed low energy constants $L_4^r$ and $L_6^r$ as well as on two $\mathcal{O}(p^6)$ low energy constants. We present some numerical results for masses and decay constants as well. We derive a relation for the scalar form factors analogous to Sirlin's relation for vector form factors.

Chiral dynamics in the meson sector at two loops

Abstract: I give a very short introduction to chiral perturbation theory and an overview of the next-to-next-to-leading order three-flavour calculations done. I discuss those relevant for an improvement in the accuracy of the measurement of V us in more detail. One major conclusion is that all needed p 6 low energy constants can be obtained from experiment via the scalar form-factor in K l3 decays

Matching the electroweak penguins Q(7) and Q(8)

Abstract: We report on recent advances on the computation of the matrix elements of the electroweak penguins Q(7) and Q(8) which are relevant for the DeltaI = 3/2 contribution to epsilon'(K) in the chiral limit. The matching of scale and scheme dependences between Wilson coefficients and these matrix elements is done analytically at NLO in alpha(S).

Chiral Dynamics in the Meson Sector at two Loops

Abstract: I give a very short introduction to Chiral Perturbation Theory and an overview of the next-to-next-to-leading order three-flavour calculations done. I discuss those relevant for an improvement in the accuracy of the measurement of $V_{us}$ in more detail. One major conclusion is that all needed $p^6$ low energy constants can be obtained from experiment via the scalar form-factor in $K_{\ell3}$ decays.

Hadronic Matrix Elements for Kaons

Abstract: We review some work done by us calculating matrix elements for Kaons. Emphasis is put on the matrix elements which are relevant to predict non-leptonic Kaon CP violating observables. In particular, we recall our results for the \hat B_K parameter which governs the \bar{K^0}-K^0 mixing and update our results for epsilon'_K including estimated all-higher-order CHPT corrections and the new results from recent analytical calculations of the \Delta I=3/2 component. Some comments on future prospects on calculating matrix elements for Kaons are also added.