Related papers: On the analysis of the pi -> e nu gamma experiment…
We present a theoretical study of the $\gamma\gamma^{*} \to \pi^+\pi^-, \pi^0\pi^0$ processes from the threshold through the $f_2(1270)$ region in the $\pi\pi$ invariant mass. We adopt the Omn\`es representation in order to account for…
We consider the first pion excitation as a sub-continuum resonance in the pseudoscalar channel, and we obtain parameters characterizing this resonance through a global fit of the Borel-parameter dependence of the field-theoretical…
The decays pi^0, eta, eta-prime -> gamma gamma are investigated up to next-to-next-to-leading order in the framework of the combined 1/N_c and chiral expansions. Without mixing of the pseudoscalar mesons the N_c independence of the pi^0 and…
The pionium decay width is evaluated in the framework of chiral perturbation theory and the relativistic bound state formalism of constraint theory. Corrections of order O(\alpha) are calculated with respect to the conventional lowest-order…
A number of recent multipole analyses from Mainz, RPI, BNL and Virginia Tech (VPI) have focused on the first resonance region. One goal common to these studies was an improved set of Delta(1232) photo-decay amplitudes. There has been…
The subprocess $nn\to ppe^-e^-$ is a key ingredient in the interpretation of nuclear neutrinoless double-beta decay. Intermediate $\Delta$ resonances may provide additional enhancements to this transition. We take a first step toward a…
The decay (B^0)bar -> pi^+ pi^- gamma has a bremsstrahlung component determined by the amplitude for (B^0)bar -> pi^+ pi^-, as well as a direct component determined by the penguin interaction V_tb V^*_td c_7 O_7. Interference of these…
We calculate the width for the omega -> pi pi decay in nuclear medium. Chiral dynamics and low-density approximation are used. At densities around twice the nuclear saturation density we estimate the partial width for the decay of the…
Final state radiation in the process $e^+e^-\to\pi^+\pi^-$ is considered for the cuts used in the analysis of KLOE data at large angles. By means of a Monte Carlo event generator FEVA, effects of non-pointlike behaviour of pions are…
It is shown that the transition amplitudes of radiative electroweak processes like $e^-e^+ \to \nu_e \ol{\nu}_e \ga$, $\ga e^- \to \nu_e \ol{\nu}_e e^-$, and $\nu_e e^- \to \nu_e e^- \ga$ can be reduced and factorized into simpler forms in…
Recent theoretical and numerical progresses of the lattice calculations of $K\to\pi\pi$ decay amplitude are reviewed.
The "pion-decay" bump is a distinct signature of the differential energy spectrum of $\gamma$-rays between 100 MeV and 1 GeV produced in hadronic interactions of accelerated particles (cosmic rays) with the ambient gas. We use the recent…
We show that the semi-leptonic decay B+ -> pi+ pi- l+ \nu_l can be used as a source of information for two-pion distribution amplitudes. The connection between these amplitudes and the B-meson decay width is achieved by the light cone sum…
An analytical expression for the spin-averaged amplitude squared of the rare muon decay $\mu^+ \to e^+e^-e^+\nu_e\bar{\nu_\mu}$ is calculated. Monte Carlo phase space simulation using the analytical expression for the amplitude has been…
We describe the interference between amplitudes $e^+e^- \to \rho \to \gamma\pi^+\pi^-$ and $e^+e^- \to \phi \to \gamma f_0 \to \gamma\pi^+\pi^-$, where $f_0$ meson is considered in the frameworks of the four-quark model and the model of the…
We consider the phenomenological description of the two pion invariant mass spectrum in the $V' \to V \pi\pi$ decays. We study the parametrization of the amplitude involving both $S$ and $D$ wave contributions. From a fit to the two pion…
We study the pion Distribution Amplitude (\pi DA) in the context of a nonlocal chiral quark model. The corresponding Lagrangian reproduces the phenomenological values of the pion mass and decay constant, as well as the momentum dependence…
A search for the decay of the tau lepton to seven charged pions and one or zero pizero mesons was performed using the BaBar detector at the PEP-II asymmetric-energy e+e- collider. The analysis uses 232.2 fb-1 of data at center-of-mass…
The arguments are put forward that the many pion decays omega ->2 pi^+ 2 pi^- pi^0 and pi^+ pi^- 3 pi^0 provide an ideal test site for testing the predictions of chiral models of the vector meson decays into many pions. Using the approach…
We report interim results of the PIBETA experiment analysis for the pion beta decay and pion radiative decay. The former is in excellent agreement with the SM predictions at the 1% accuracy level.