Related papers: Electromagnetic corrections to gamma pi(+) -> pi(0…
We perform a theoretical study based on dispersion relations of the reaction \gamma\gamma\to \pi^0\pi^0 emphasizing the low energy region. We discuss how the f_0(980) signal emerges in \gamma\gamma\to \pi\pi within the dispersive approach…
The effect of perturbative QCD interactions on the high energy scattering of electroweak vector bosons, when the exchanged channel has pion quantum numbers, is considered. The chiral anomaly is shown to appear in the couplings of particular…
The cusp structure at the $\pi^+\pi^-$ threshold in the $\pi^0\pi^0$ invariant mass spectrum serves as a sensitive probe for extracting the $S$-wave $\pi\pi$ scattering lengths in processes where an $S$-wave $\pi^0\pi^0$ pair is produced in…
Electroproduction of pions on the nucleon near the threshold is analyzed within the framework of baryon chiral perturbation theory. We give a thorough discussion of the low--energy theorems related to charged and neutral…
We re-evaluate the electromagnetic corrections to eta --> 3 pi decays at next-to-leading order in the chiral expansion, arguing that effects of order e^2(m_d-m_u) disregarded so far are not negligible compared to other contributions of…
Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e- gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7 estimated background events. With K+- -> pi+- pi0D as normalisation channel, the…
Using constituent quarks coupled to a linear sigma model at nonzero temperature, I show that many anomalous mesonic amplitudes, such as $\pi^0 \rightarrow \gamma \gamma$, vanish in a chirally symmetric phase. Processes which are allowed,…
The processes $\gamma\gamma\to\pi^0\pi^0\pi^0$ and $\gamma\gamma\to \pi^+ \pi^- \pi^0$ are considered in Generalized Chiral Perturbation theory, in view of their potential sensitivity to the mechanism of spontaneous breaking of chiral…
We consider the forward-backward pion charge asymmetry for the e^{+}e^{-}\to\pi^{+}\pi^{-}\gamma process. At tree level we consider bremsstrahlung and double resonance contributions. Although the latter contribution is formally sub-leading,…
We use chiral perturbation theory to evaluate the scattering amplitude for the process Pi^+ K^- to Pi^+ K^- at leading and next-to-leading orders in the chiral counting and in the presence of isospin breaking effects. We also discuss the…
This paper presents an analysis of pi- Pb -> X- Pb -> pi-pi-pi+ Pb events at 190 GeV/c beam momentum and very low four-momentum transfer t'<0.001 GeV^2/c^2. Coherent scattering off the nucleus as a whole dominates with contributions from…
1. Introduction: a) motivations, b) status, c) purpose, d) results 2. Kinematics and couplings 3. Decay amplitude (analytic expression): a) tree level, b) one loop 4. Decay width (numerical): a) diphoton energy spectrum [energy cut] 5.…
This dissertation studies the quantum anomalous effects on the description of high energy electrodynamics. We argue that on the temperatures comparable to the electroweak scale, characteristic for the early Universe and objects like neutron…
A rigorous multipole analysis of the recent {\gamma}p -> \pi^{0}p cross section measurement is presented. The data were taken using the photon spectrometer TAPS at the tagged photon beam of the Mainz microtron. The s and p wave multipoles…
We calculate the cross-section for the thermal $n+p\rightarrow d+\gamma$ process in chiral perturbation theory to next-to-next-to-leading order using heavy-fermion formalism. The exchange current correction is found to be $(4.5\pm 0.3)~\%$…
The inverse amplitude method has previously been successfully applied to $\pi\pi$ scattering in order to extend the range of applicability of chiral perturbation theory. However, in order to take the chiral zeros into account…
The integrated cross sections of high-energy $e^+e^-$ electroproduction by an electron in an atomic field is studied. Importance of various contributions to these cross sections is discussed. It is shown that the Coulomb corrections are…
We demonstrate that chiral-odd dimeson generalized distribution amplitudes (CO-GDAs) -- nonperturbative objects encoding the transition of a quark-antiquark pair into two mesons -- can be accessed in high-energy $e^- e^+$ annihilation into…
Fermilab E781 plans measurements of gamma-Sigma and $\gamma$-pion interactions using a 600 GeV beam of Sigmas and pions, and a virtual photon target. Pion polarizabilities and radiative transitions will be measured in this experiment. The…
Using dispersion theory, the electromagnetic Sigma-to-Lambda transition form factors are expressed as the product of the pion electromagnetic form factor and the $\Sigma\bar{\Lambda}\to\pi\pi$ scattering amplitudes with the latter estimated…