Chiral Meson Physics at Two Loops

An overview of Chiral Perturbation Theory calculations in the mesonic sector at the two Loop level is given. Discussed in some detail are the partially quenched case relevant for lattice QCD, the general fitting procedures and $\pi\pi$,$\pi K$ scattering as well as the determination of $V_{us}$ and $K_{\ell3}$ decays.Comment: 7 pages, Invited plenary talk presented at the 19th European Few-Body conference, Groningen, The Netherlands, August 23-27, 200

Chiral Dynamics in the Meson Sector at two Loops

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.Comment: 5 pages, Talk presented at CIPANP 2003, Conference on the Intersections of Particle and Nuclear Physics, New York May 19-24, 200

ChPT loops for the lattice: pion mass and decay constant, HVP at finite volume and nnˉn\bar n-oscillations

I present higher loop order results for several calculations in Chiral perturbation Theory. 1) Two-loop results at finite volume for hadronic vacuum polarization. 2) A three-loop calculation of the pion mass and decay constant in two-flavour ChPT. For the pion mass all needed auxiliary parameters can be determined from lattice calculations of $\pi\pi$-scattering. 3) Chiral corrections to neutron-anti-neutron oscillations.Comment: 8 pages, presented at Lattice 2017, the 35th International Symposium on Lattice Field Theory, Granada, Spain, 18-24 June 201

Quark Mass dependence at Two Loops for Meson Properties

This talks contains a short introduction to Chiral Perturbation Theory and the existing calculations to two-loop order in the mesonic sector. I include a discussion on which quantities the expansion can be organized in. The present best values of the Low-Energy-Constants as determined from continuum physics are given as well as the assumptions underlying the fits to experimental data. I present plots of masses, decay constants and $f_+(0)$ in $K_{\ell3}$ as a function of quark or meson masses. The talk ends with a list of things for which it would be extremely useful to have good results from lattice QCD calculations.Comment: 15 pages, plenary talk at T he XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, Germany. v2: some clarifying statements adde

On the Hadronic light-by-light contribution to the muon g−2g-2

This talk is about the hadronic light-by-light contribution to the muon anomalous magnetic moment, mainly our old work but including some newer results as well. It concentrates on the model calculations. Most attention is paid to pseudo-scalar exchange and the pion loop contribution. Scalar, $a_1$-exchange and other contributions are shortly discussed as well. For the $\pi^0$-exchange a possible large cancellation between connected and disconnected diagrams is expected.Comment: 9 pages, invited talk presented at FCCP2017 - Workshop on "Flavour changing and conserving processes," 7-9 September 2017, Anacapri, Capri Island, Italy. arXiv admin note: substantial text overlap with arXiv:1510.0579

Radiative and semileptonic decays in Chiral Perturbation Theory

I give a short overview of what has been done in radiative and semileptonic Kaon decays in Chiral Perturbation Theory. This includes for semileptonic decays the work which has been done to order $p^6$ including preliminary results of isospin breaking to that order in $K_{\ell3}$. For the radiative decays I mainly present some results from recent work concerning $K_{\ell3\gamma}$.Comment: 5 pages, presented at Kaon International Conference (KAON07), May 21-25, 2007, Laboratori Nazionali di Frascati dell'INFN, Frascati, Ital

Eta and Eta' physics

This talk describes the reasons why $\eta$ and $\eta^\prime$ decays are an interesting topic of study for both theory and experiment. The main part discusses the results of the recent calculation of $\eta\to3\pi$ at two-loop order in ChPT. Some puzzling aspects of the results compared to earlier dispersive calculations are highlighted. I also like to remind the reader of the use of $\eta$ and $\eta^\prime$ decays for studying the anomaly.Comment: 10 pages, {Plenary talk given at MENU07, September 10-14, 2007 J\"ulich, German