Related papers: Extracting the chiral anomaly from $e^+e^-\to 3\pi…
The next-to-leading order chiral pion-nucleon Lagrangian contains seven finite low-energy constants. Two can be fixed from the nucleon anomalous magnetic moments and another one from the quark mass contribution to the neutron-proton mass…
Within renormalizable theories the triangle diagram correctly reproduces the lifetime of the neutral pion $\pi ^0$. However, effective relativistic quark models which contain a second scale besides the quark mass seem unable to give the…
We present a dispersive analysis of the decay amplitude for $\eta'\to\eta\pi\pi$ that is based on the fundamental principles of analyticity and unitarity. In this framework, final-state interactions are fully taken into account. Our…
Using a large acceptance calorimeter and a stopped pion beam we have made a precise measurement of the rare Pi+ -> Pi0 e+ Nu,(pi_beta) decay branching ratio. We have evaluated the branching ratio by normalizing the number of observed…
The pion decay constant $F_{\pi}$ plays an important role in QCD and in Chiral Perturbation Theory. It is hardly known, however, that a corresponding constant exists in the Schwinger model with $N_{\rm f} \geq 2$ degenerate fermion flavors.…
The temperature dependence of the anomalous sector of the effective action of fermions coupled to external gauge and pseudo-scalar fields is computed at leading order in an expansion in the number of Lorentz indices in two and four…
We investigate decay and production of neutral pions in strong magnetic fields. In the presence of strong magnetic fields, transition between a neutral pion and a virtual photon becomes possible through the triangle diagram relevant for the…
The decays $\rho^0\to 2\pi^+2\pi^-$ and $\rho^0\to 2\pi^0\pi^+\pi^-$ are studied using various effective Lagrangians for $\pi$ and $\rho$ (and in some cases $a_1$) mesons, all of which respect the approximate chiral symmetry of the strong…
Several lattice collaborations performing simulations with 2+1 light dynamical quarks have experienced difficulties in fitting their data with standard Nf=3 chiral expansions at next-to-leading order, yielding low values of the quark…
Using a hadronic framework, we derive an explicit expression for photon production from neutral pions in a weak background magnetic field. Our calculation is built on the proton triangle diagram with an effective Yukawa $\pi^0$-proton…
We derive an estimate for the ratio of the rho mass and the pion decay constant from an analysis of vector and axial-vector two-point functions using large-Nc, lowest-meson dominance and the operator product expansion, in the chiral limit.…
We calculate at two-loop order in chiral perturbation theory the electromagnetic corrections to the dominant two-pion exchange nucleon-nucleon interaction that is generated by the isoscalar $\pi N$ contact-vertex proportional to the large…
We analyze elastic-pion nucleon scattering to third order in the so-called small scale expansion. It is based on an effective Lagrangian including pions, nucleons and deltas as active degrees of freedom and counting external momenta, the…
Based on the Weinberg lagrangian or, in a new language, the lagrangian of hidden local symmetry added with the term induced by the anomalous lagrangian of Wess and Zumino, the dynamics of the decays rho to 4 pi and omega to 5 pi is…
We study the axion and axion-like particle production from the $\eta\to\pi\pi a$ decay within the $SU(3)$ chiral perturbation theory up to the one-loop level. The conventional $SU(3)$ chiral low energy constants are found to be able to…
The differential cross sections for $\pi^- p \to \gamma n$ and $\pi^+ n \to \gamma p$ are computed up to $O(p^3)$ in heavy baryon chiral perturbation theory (HBChPT). The expressions at $O(p)$ and $O(p^2)$ have no free parameters. There are…
We present results for pion polarizabilities predicted using dispersion relations from our earlier Amplitude Analysis of world data on two photon production of meson pairs. The helicity-zero polarizabilities are rather stable and…
Recent attempts to determine the pion polarizability by dispersion relations yield values that disagree with the predictions of chiral perturbation theory. These dispersion relations are based on specific forms for the absorptive part of…
We use the recently measured accurate BaBaR data on the modulus of the pion electromagnetic form factor, $F_\pi(t)$, up to an energy of 3 GeV, the I=1 $P$-wave phase of the $\pi\pi$ scattering amplitude up to the $\omega-\pi$ threshold, the…
In this study, we analyze the first measurement of the electron-positron invariant mass spectrum in $J/\psi \to \pi^0 e^+e^-$ by BESIII, using the framework of resonance chiral theory. Our results indicate that both strong interaction and…