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Johan Bijnens

Publications and source records attributed to Johan Bijnens.

At least 145 records · Page 8Linked to original sources
arXiv2002

Effective Field Theories of QCD

These are the proceedings of the workshop on ``Effective Field Theories of QCD'' held at the Physikzentrum Bad Honnef of the Deutsche Physikalische Gesellschaft, Bad Honnef, Germany from November 26 to 30, 2001. The workshop concentrated on Chiral Perturbation Theory in its various settings, its relations with lattice QCD and dispersion theory and the use of effective field theories in systems with one, two or more nucleons as well as at high baryon densities. Included are a short contribution per talk and a listing of some review papers on the subject.

hep-ph↗
arXiv2001

Matching the Electroweak Penguins $Q_7$, $Q_8$ and Spectral Correlators

Exact analytical expressions for the $ΔS=1$ coupling $\im G_E$ in terms of observable spectral functions are given. This coupling determines the size of the $ΔI=3/2$ contribution to $ε'$. We show analytically how the scheme-dependence and scale dependences vanish to all orders in $1/N_c$ and NLO in $α_S$ explicitly both for $Q_7$ and $Q_8$. Numerical results are derived for both $Q_7$ and $Q_8$ from the $τ$-data and known results on the scalar spectral functions. In particular we study the effect of all higher dimension operators. The coefficients of the leading operators in the OPE of the needed correlators are derived to NLO in $α_S$.

hep-ph↗
arXiv2001

Chiral Lagrangians

An overview of the field of Chiral Lagrangians is given. This includes Chiral Perturbation Theory and resummations to extend it to higher energies, applications to the muon anomalous magnetic moment, $ε^\prime/ε$ and others.

hep-ph↗
arXiv2001

Effects of different Form-factors in Meson-Photon-Photon Transitions and the Muon Anomalous Magnetic Moment

The exact form of the form-factor associated with a meson-photon-photon vertex is not known. Different suggestions exist, based on constraints from QCD and on recent experiments. Four different form-factors are studied in this article. We calculate decay rates for the decays $π^{0}\to γγ$, $η\to γe^{+}e^{-}$, $η\to μ^{+}μ^{-} e^{+}e^{-}$} and $η\to e^{+}e^{-} e^{+}e^{-}$ and cross sections for the processes $e^{+}e^{-}\to PS e^{+}e^{-}$, where $PS=π^{0}$, $η$ or $η'$. The results depend on the choice of form-factor and we examine if the differences are large enough to distinguish in upcoming experiments. The dominant part of the light-by-light contribution to the muon anomalous magnetic moment is also calculated. Here the uncertainty around the choice of form-factor implies that it is possible to estimate a smallest error in the theoretical value of this contribution.

hep-ph↗
arXiv2000

Report of the Working Group on Goldstone Bosons

An overview is presented of the talks in the working group on Goldstone Bosons. Topics touched on are CP-violation in the Kaon system, rare Kaon decays, $ππ$-scattering, $ϕ$-meson decays, scalar mesons, form-factors and polarizabilities, $η$-decays, chiral symmetry breaking, connections with QCD at short-distances and effective theories for electroweak physics.

hep-ph↗
arXiv2000

Large Extra Dimensions in Rare Decays

The prospect of experimental verification of the large extra dimension scenario in rare decays is discussed. The case of J/Ψand Υto photon + missing energy is calculated in detail, and it is shown that the limit on the compactification scale M_S lies at present in the ten GeV range. In contrast to the quarkonium systems, signals in Kaon and Pion decays will be small.

hep-ph↗
arXiv2000

$K_{l4}$ at two-loops and CHPT predictions for $ππ$-scattering

We present the results from our two-loop calculations of masses, decay-constants, vacuum-expectation-values and the $K_{\ell4}$ form-factors in three-flavour Chiral Perturbation Theory (CHPT). We use this to fit the $L_i^r$ to two-loops and discuss the ensuing predictions for $ππ$-threshold parameters.

hep-ph↗
arXiv2000

Weak Interactions of Light Flavours

An overview is given of weak interaction physics of the light flavours. It starts with the definition of the CKM matrix and the measurement of its components in the light-flavour sector via semi-leptonic decays. The main part of the lectures is devoted to non-leptonic decays with a main emphasis on analytical calculations of $K\toππ$ and $K^0\leftrightarrow \kob$ mixing. It finishes with an overview of Chiral Perturbation Theory in $K\to3π$ and of rare Kaon decays.

hep-ph↗
arXiv2000

Chiral Limit Prediction for epsilon'/epsilon at NLO in 1/N_c

We report on a calculation of $ε_K'/ε_K$ at next-to-leading in the $1/N_c$ expansion and to lowest order in Chiral Perturbation Theory. We discuss the short-distance matching, the scale and scheme dependence as well as the long-distance short-distance matching. We include the two known chiral corrections to our result and discuss further order $p^4$ corrections to it.

hep-ph↗
arXiv2000

epsilon'/epsilon in the Chiral Limit

The $K\toππ$ system is analyzed in the chiral limit within the Standard Model. We discuss how to connect the short-distance running in the $|ΔS|=1$ case to the matrix-elements calculated in a low-energy approximation in a scheme-independent fashion. We calculate this correction and the resulting Wilson Coefficients. The matrix elements are calculated to next-to-leading order in the $1/N_c$ expansion and combined with the Wilson coefficients to calculate the two isospin amplitudes and $ε_K^\prime$. The $ΔI=1/2$ rule is reproduced within expected errors and we obtain a substantially larger value for $ε_K^\prime/ε_K$ than most other analysises. We discuss the reasons for this difference. We also suggest that the $X$-boson method is an option for lattice QCD calculations.

hep-ph↗
arXiv1999

Scheme Dependence of Weak Matrix Elements in the $1/N_c$ Expansion

We show how the scheme- and scale-dependence of the short-distance operator product expansion with four-quark operators can be correctly accounted for in the framework of the $1/N_c$-expansion once the hadronization of two-quark currents has been fixed. We show formulas explicitly in the case of the $B_K$-parameter. We then use them with our earlier estimates of the long-distance effects. We compare Chiral Perturbation Theory at Leading- and Next-to-Leading-Order with the ENJL model results in the chiral limit. Good matching between the long- and short-distance regimes is obtained and our final value for the physical scheme independent $\hat B_K$ is $0.77\pm0.05\pm0.05$.

hep-ph↗
arXiv1999

Models of Low Energy Effective Theory applied to Kaon Non-leptonic Decays and Other Matrix Elements

In this talk I describe work on computing non-leptonic matrix elements consistently with both long and short distance contributions included. On the simpler example of the $π^+$-$π^0$ mass difference I explain in detail the matching procedure and the difference between various low-energy models. I then explain the new difficulties in non-leptonic Kaon decays and how the matching here can in principle be done in the same way when scheme dependences are correctly accounted for. In the end I summarize the results J. Prades and I obtain for the $ΔI=1/2$ rule and $B_6$.

hep-ph↗
arXiv1999

The $ΔI=1/2$ rule and other matrix elements

Recent work by J.Prades and myself on $K\toππ$ is described. The method we use to consistently connect long and short distances is described and numerical results for the $ΔI=1/2$ rule and on $B_6$, the parameter relevant for the strong part of $ε'/ε$, are given in the chiral limit.

hep-ph↗
arXiv1999

I : Chiral Perturbation for Kaons II: The $ΔI=1/2$-rule in the Chiral Limit

I : Chiral Perturbation Theory is introduced and its applications to semileptonic and nonleptonic kaon decays are discussed. II: The method of large $N_c$ is used to calculate $K\toππ$ nonleptonic matrix elements, in particular the matching procedure between long and short-distance evolution that takes all scheme dependence correctly into account is discussed. Numerical results reproduce the $ΔI=1/2$ rule without the introduction of any free parameters.

hep-ph↗
arXiv1999

Progress in $K\toππ$ Decays

Recent work by J.~Prades and myself on $K\toππ$ is described. The first part describes our method to connect in a systematic fashion the short-distance evolution with long-distance matrix-element calculations taking the scheme dependence of the short-distance evolution into account correctly. In the second part I show the results we obtain for the $ΔI=1/2$ rule in the chiral limit.

hep-ph↗