We employ a Dyson-Schwinger equation model to effect a unified and uniformly accurate description of light- and heavy-meson observables, which we characterise by heavy-meson leptonic decays, semileptonic heavy-to-heavy and heavy-to-light transitions - B -> D*, D, rho, pi; D -> K*, K, pi, radiative and strong decays - B(s)* -> B(s) gamma; D(s)* -> D(s) gamma, D pi, and the rare B-> K* gamma flavour-changing neutral-current process. We elucidate the heavy-quark limit of these processes and, using a model-independent mass formula valid for all nonsinglet pseudoscalar mesons, demonstrate that their mass rises linearly with the mass of their heaviest constituent. In our numerical calculations we eschew a heavy-quark expansion and rely instead on the observation that the dressed c,b-quark mass functions are well approximated by a constant, interpreted as their constituent-mass: we find M_c=1.32 GeV and M_b=4.65 GeV. The calculated heavy-meson leptonic decay constants and transition form factors are a necessary element in the experimental determination of CKM matrix elements. The results also show that this framework, as employed hitherto, is well able to describe vector meson polarisation observables.Comment: 32 pages, 7 figures, REVTEX. Some quantitative modification of tables and figures: calculation of additional processes. To appear in Phys. Rev.

We use the Mellin-Barnes representation in order to improve the theoretical estimate of mass corrections to the width of light pseudoscalar meson decay into a lepton pair, P → l + l − . The full resummation of the terms ln(m 2 l /Λ 2 ) m 2 l /Λ 2 n and m 2 l /Λ 2 n to the decay amplitude is performed, where m l is the lepton mass and Λ ≈ m ρ is the characteristic scale of the P → γ * γ * form factor.The total effect of mass corrections for the e + e − channel is negligible and for the µ + µ − channel its order is of a few per cent.

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Abstract. We investigate the ground-state energy of the π − p atom (pionic hydrogen) in the framework of QCD+QED. In particular, we evaluate the strong energy-level shift. We perform the calculation at nextto-leading order in the low-energy expansion in the framework of the relevant effective field theory. The result provides a relation between the strong energy shift and the pion-nucleon S-wave scattering lengths -evaluated in pure QCD -at next-to-leading order in isospin breaking and in the low-energy expansion. We compare our result with available model calculations.

We complete the recalculation of the available two-loop expressions for the reaction γγ → ππ in the framework of chiral perturbation theory. Here, we present the results for charged pions. The cross section and the values of the dipole polarizabilities agree very well with the earlier calculation, provided the same set of low-energy constants (LECs) is used. With updated values for the LECs at order p 4 , we find for the dipole polarizabilities (α 1 − β 1 ) π ± = (5.7 ± 1.0) × 10 −4 fm 3 , which is in conflict with the experimental result recently reported by the MAMI Collaboration.