Anomalous decay and scattering processes of the eta meson

We amend a recent dispersive analysis of the anomalous $\eta$ decay process $\eta\to\pi^+\pi^-\gamma$ by the effects of the $a_2$ tensor meson, the lowest-lying resonance that can contribute in the $\pi\eta$ system. While the net effects on the measured decay spectrum are small, they may be more pronounced for the analogous $\eta'$ decay. There are nonnegligible consequences for the $\eta$ transition form factor, which is an important quantity for the hadronic light-by-light scattering contribution to the muon's anomalous magnetic moment. We predict total and differential cross sections, as well as a marked forward-backward asymmetry, for the crossed process $\gamma\pi^-\to\pi^-\eta$ that could be measured in Primakoff reactions in the future.Comment: 12 pages, 11 figures; v2 matches version published in EPJ

Dispersion-theoretical analysis of the D^+ --> K^- pi^+ pi^+ Dalitz plot

We study the Dalitz plot of the Cabibbo-favored charmed-meson decay $D^+\to K^-\pi^+\pi^+$ using dispersion theory. The formalism respects all constraints from analyticity and unitarity, and consistently describes final-state interactions between all three decay products. We employ pion-pion and pion-kaon phase shifts as input, and fit the pertinent subtraction constants to Dalitz plot data by the CLEO and FOCUS collaborations. Phase motions of resonant as well as nonresonant amplitudes are discussed, which should provide crucial input for future studies of CP violation in similar three-body charm decays.Comment: 32 pages, 7 figures, version published in JHE

Consistent Dalitz plot analysis of Cabibbo-favored D+→Kˉππ+D^+ \to \bar{K} \pi \pi^+ decays

We resume the study of the Cabibbo-favored charmed-meson decays $D^+ \to \bar{K} \pi \pi^+$ in a dispersive framework that satisfies unitarity, analyticity, and crossing symmetry by construction. The formalism explicitly describes the strong final-state interactions between all three decay products and relies on pion-pion and pion-kaon phase shift input. For the first time, we show that the $D^+ \to K_S \pi^0 \pi^+$ Dalitz plot obtained by the BESIII collaboration as well as the $D^+ \to K^- \pi^+ \pi^+$ Dalitz plot data by CLEO and FOCUS can be described consistently, exploiting the isospin relation between the two coupled decay channels that provides better constraints on the subtraction constants.Comment: 8 pages, 2 figures; v2: discussion extended, references added, matches published versio

Isospin violation in low-energy charged pion-kaon scattering

We evaluate the isospin breaking corrections to the scattering amplitude \pi^- K^+ -> \pi^- K^+ at threshold in the framework of chiral perturbation theory. This channel is of particular interest for the strong 2S-2P energy level shift in pion-kaon bound states. While a prediction of this level shift is hampered by a large uncertainty in the isoscalar scattering length, we find only a moderate uncertainty of about 3% in the electromagnetic corrections which are relevant for the extraction of the scattering lengths from experimentComment: 9 pp, 2 fig

Baryon form factors in chiral perturbation theory

We analyze the electromagnetic form factors of the ground state baryon octet to fourth order in relativistic baryon chiral perturbation theory. Predictions for the \Sigma^- charge radius and the \Lambda-\Sigma^0 transition moment are found to be in excellent agreement with the available experimental information. Furthermore, the convergence behavior of the hyperon charge radii is shown to be more than satisfactory.Comment: 22 pp, LaTeX2e, FZJ-IKP(TH)-2000-2

Extracting the chiral anomaly from gamma pi --> pi pi

We derive dispersive representations for the anomalous process gamma pi --> pi pi with the pi pi P-wave phase shift as input. We investigate how in this framework the chiral anomaly can be extracted from a cross-section measurement using all data up to 1 GeV, and discuss the importance of a precise representation of the gamma pi --> pi pi amplitude for the hadronic light-by-light contribution to the anomalous magnetic moment of the muon.Comment: 10 pages, 3 figures; version published in Phys. Rev.

A new parametrization for the scalar pion form factors

We derive a new parametrization for the scalar pion form factors that allows us to analyze data over a large energy range via the inclusion of resonances, and at the same time to ensure consistency with the high-accuracy dispersive representations available at low energies. As an application the formalism is used to extract resonance properties of excited scalar mesons from data for $\bar B^0_s\to J/\psi \pi\pi$. In particular we find for the pole positions of $f_0(1500)$ and $f_0(2020)$ $1465\pm 18 - i (50\pm 9)\,\text{MeV}$ and $1910\pm 50 - i(199\pm 40)\,\text{MeV}$, respectively. In addition, from their residues we calculate the respective branching ratios into $\pi\pi$ to be $(58\pm31)\%$ and $(1.3\pm1.8)\%$.Comment: 18 pages, 11 figures; v2: discussion+figure on pi pi --> K Kbar added, version published in EPJ