Related papers: How pi0 -> gamma gamma changes with temperature
Using the close relationship between the low--energy constants of chiral perturbation theory and the chiral invariant interactions of the vector meson resonances with the pseudoscalar mesons, we investigate the process $\rho^0 \ra \pi^+…
Two closely related topological phenomena are studied at finite density and temperature. These are chiral anomaly and Chern-Simons term. By using different methods it is shown that $\mu^2 = m^2$ is the crucial point for Chern-Simons at zero…
Axion-pion scattering amplitudes at finite temperatures are calculated within chiral perturbation theory up to the one loop level. Unitarization procedure is implemented to these amplitudes in order to extend the applicable range of energy…
With usage of the Low theorem the general expression for amplitude of radiative kaon decay \k+ \to \pi+\pi0\gamma is determined.
We calculate the $00^{++}$-wave two-meson spectra for the reactions $\gamma\gamma\to\pi^0\pi^0$, $\gamma\gamma\to\pi^+\pi^-$, $\gamma\gamma\to K^0\bar K^0$ and $\gamma\gamma\to K^+ K^-$ on the basis of: (i) the results of the $K$-matrix…
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 analyse the radiative decay $\eta \to \pi^+\pi^- \pi^0\gamma$ in the low--energy expansion of the Standard Model. We employ the notion of ``generalized bremsstrahlung'' to take full advantage of the theoretical and experimental…
We propose a chiral random matrix model which properly incorporates the flavor-number dependence of the phase transition owing to the \UA(1) anomaly term. At finite temperature, the model shows the second-order phase transition with…
We compute low temperature corrections to the electromagnetic mass difference of pions in the chiral limit. The computation is done in a model independent way in the framework of chiral perturbation theory, using the background field method…
A simple method is used to extrapolate the form factor for the process gamma* gamma *--->pi^0 when two virtual photons produce a pi ^0 from the region of large spacelike photon virtualities to the experimentally accessible case when one of…
We discuss the reaction $\pi^- e^- \to \pi^- e^- \pi^{0}$ with the purpose of obtaining information on the $\gamma \pi \to \pi\pi$ anomalous amplitude ${\cal F}_{3\pi}$. We compare a full calculation at ${\cal O}(p^6)$ in chiral…
The first observation of the decay K^+ --> pi^+ gamma gamma is reported. A total of 31 events was observed with an estimated background of 5.1 +- 3.3 events in the pi+ momentum range from 100 MeV/c to 180 MeV/c. The corresponding partial…
With a study of bulk GaAs and GaP, we report detailed infrared spectra and their temperature dependence from first principles. Fine features and low-temperature trends in the predicted response are confirmed by experiment. The spectra are…
Statistical average of the axial current is evaluated on the basis of the covariant Wigner function. In the resulting formula, chemical potential $\mu$, angular velocity $\Omega$ and acceleration $a$ enter in combination $\mu \pm (\Omega…
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…
We show in detail how the presence of a heat bath of photons effectively gives charged particles in the final state of a decay process a temperature-dependent mass, and changes the effective strength of the force responsible for the decay.…
The decays of the omega meson in a heat bath of thermally excited pions is studied within the framework of real-time thermal field theory using an appropriate effective Lagrangian. We show that the omega meson spectrum broadens considerably…
The $\gamma\gamma \to \pi^0 \pi^0 \pi^0$ and $\gamma\gamma \to \pi^+ \pi^- \pi^0$ amplitudes are discussed in the general context of Chiral Perturbation Theory (ChPT) to $O(p^6)$. Chiral loops are found to play a major role. This makes…
A thermal Finite Energy QCD Sum Rule is used to determine the temperature behaviour of the $\omega \rho \pi$ strong coupling. This coupling decreases with increasing $T$ and vanishes at the critical temperature, a likely signal for quark…
The anomaly in the vacuum expectation value of the product of axial and two vector currents (AVV) in QCD is investigated. The goal is to determine from its value the $\pi^0 \to 2 \gamma$ decay width with high precision. The sum rule for AVV…