alpha gamma gamma vertex in a crossed external field

title: On collinearization of quarks in the quark-gluon decays of heavy orthoquarkonia
abstract: The decay of heavy orthoquarkonium into quark-antiquark pair and two gluons is considered. The differential probability of the decay in the tree approximation is calculated and the probability distributions of quarks and gluons are obtained. The collinear enhancement of the bottomonium decay is shown to take place at the u\={u}--, d\={d} and s\={s}-- pair production and to be absent at the c\={c}-- production. Some other peculiarities of the considered decays are discussed.

title: On Collinearization of Quarks in Quark-Gluon Decays of Heavy Orthoquarqonia
abstract: The decay of heavy orthoquarkonium into quark-antiquark pair and two gluons is considered. The differential probability of the decay in the tree approximation is calculated and the final quark mass influence on the quark and gluon distribution functions is studied. It is shown that the collinear strengthening of the bottomonium decay probability takes place at the $u \bar u$-, $d \bar d$- and $s \bar s$- pair production and is absent at the $c \bar c$- production.

title: Axion in an external electromagnetic field
abstract: We investigate the effective interaction of a pseudoscalar particle with two photons in an external electromagnetic field in the general case of all external particles being off the mass shell. This interaction is used to study the radiative decay $\stackrel{\ensuremath{\rightarrow}}{a}\ensuremath{\gamma}\ensuremath{\gamma}$ of the axion, a pseudoscalar particle associated with the Peccei-Quinn symmetry, and the crossing channel of photon splitting $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}\ensuremath{\gamma}a$. It is shown that the external field removes the suppression associated with the smallness of the axion mass and so leads to the strong catalysis of these processes. The field-induced axion emission by the photon is analyzed as one more possible source of energy loss by astrophysical objects.

title: Photon-axion processes in a crossed external field

title: Magnetic-field influence on radiative axion decay into photons of the same polarization
abstract: The decays of a pseudoscalar particle, the axion, into two photons of the same polarization are studied in the model involving direct axion-electron coupling. These processes, which are forbidden in a vacuum because of a pseudoscalar nature of the axion, become possible in a magnetic field. It is shown that the kinematics of ultrarelativistic-axion decay substantially depends on photon polarizations. The probability of radiative axion decay in the limit of a strong magnetic field substantially exceeds the corresponding probability in a vacuum.

title: B ---> rho gamma decay in the large energy effective theory
abstract: The branching ratio for the $B \to \rho \gamma$ decay in the next-to-leading order (NLO) in the strong coupling $\alpha_s$ and in leading power in $\Lambda_{\rm QCD}/m_B$ is presented. The corrections are combined the hard-vertex, hard-spectator and annihilation contributions and found to be large. The theoretical expectation for the branching ratios, the isospin-violating ratio and for the direct CP-asymmetry in the $B \to \rho \gamma$ decays are presented.

title: MASS EFFECTS IN THE QUARK–GLUON DECAYS OF HEAVY PARAQUARKONIA
abstract: Quark–gluon decays of heavy paraquarkonia are investigated with account of the masses of final quarks. The decay widths and the energy distributions of the final quarks and gluons are calculated in dependence on the relative quark masses. The strong collinear enhancement of the gluon energy distribution at the end of the spectrum is shown to take place in all such decays of ηc and ηb mesons except the decay . The total decay width is shown to have an essential dependence on the final quark masses. The corresponding branching ratios of ηc and ηb mesons are numerically estimated with a good agreement of with experimental data on ηc decays.