Magnetic polarizabilities of light mesons in SU(3)SU(3) lattice gauge theory

We investigate the masses (ground state energies) of neutral pseudoscalar and vector meson in $SU(3)$ lattice gauge theory in strong abelian magnetic field. The energy of $\rho^0$ meson with zero spin projection $s_z=0$ on the axis of the external magnetic field decreases, while the energies with non-zero spins $s_z=-1$ and $+1$ increase with the field. The energy of $\pi^0$ meson decrease as a function of the magnetic field. We calculated the magnetic polarizabilities of pseudoscalar and vector mesons for lattice volume $18^4$. For $\rho^0$ with spin $|s_z|=1$ and $\pi^0$ meson the extrapolations to zero lattice spacing have been done. We do not observe any evidence in favour of tachyonic mode existence.Comment: 9 pages, 13 figure

Dispersive approach to the axial anomaly and nonrenormalization theorem

Anomalous triangle graphs for the divergence of the axial-vector current are studied using the dispersive approach generalized for the case of higher orders of perturbation theory. The validity of this procedure is proved up to two-loop level. By direct calculation in the framework of dispersive approach we have obtained that the two-loop AVV amplitude is equal to zero. According to the Vainshtein's theorem the transversal part of the anomalous triangle is not renormalized in the chiral limit. We generalize this theorem for tha case of finite fermion mass in the triangle loop.Comment: 12 pages, version to appear in Physical Review

Semiclassical limit for Dirac particles interacting with a gravitational field

The behavior of spin-1/2 particle in a weak static gravitational field is considered. The Dirac Hamiltonian is diagonalized by the Foldy-Wouthuysen transformation providing also the simple form for the momentum and spin polarization operators. The operator equations of momentum and spin motion are derived for a first time. Their semiclassical limit is analyzed. The dipole spin-gravity coupling in the previously found (another) Hamiltonian does not lead to any observable effects. The general agreement between the quantum and classical analysis is established, contrary to several recent claims. The expression for gravitational Stern-Gerlach force is derived. The helicity evolution in the gravitational field and corresponding accelerated frame coincides, being the manifestation of the equivalence principle.Comment: 8 pages, no figures; version to appear in Physical Review

Photon distribution amplitudes and light-cone wave functions in chiral quark models

The leading- and higher-twist distribution amplitudes and light-cone wave functions of real and virtual photons are analyzed in chiral quark models. The calculations are performed in the nonlocal quark model based on the instanton picture of QCD vacuum, as well as in the spectral quark model and the Nambu--Jona-Lasinio model with the Pauli-Villars regulator, which both treat interaction of quarks with external fields locally. We find that in all considered models the leading-twist distribution amplitudes of the real photon defined at the quark-model momentum scale are constant or remarkably close to the constant in the $x$ variable, thus are far from the asymptotic limit form. The QCD evolution to higher momentum scales is necessary and we carry it out at the leading order of the perturbative theory for the leading-twist amplitudes. We provide estimates for the magnetic susceptibility of the quark condensate $\chi_m$ and the coupling $f_{3\gamma}$, which in the nonlocal model turn out to be close to the estimates from QCD sum rules. We find the higher-twist distribution amplitudes at the quark model scale and compare them to the Wandzura-Wilczek estimates. In addition, in the spectral model we evaluate the distribution amplitudes and light-cone wave functions of the $\rho$-meson.Comment: 24 pages, 15 figure

Tensor polarizability of the vector mesons from SU(3)SU(3) lattice gauge theory

The magnetic dipole polarizabilities of the vector $\rho^0$ and $\rho^{\pm}$ mesons in $SU(3)$ pure gauge theory are calculated in the article. Based on this the authors explore the contribution of the dipole magnetic polarizabilities to the tensor polarization of the vector mesons in external abelian magnetic field. The tensor polarization leads to the dilepton asymmetry observed in non-central heavy ion collisions and can be also estimated in lattice gauge theory.Comment: 18 pages, 7 figures, 6 table

Decay anisotropy of e+e- sources from pN and pd collisions

A full calculation of lepton-pair angular characteristics is carried out for e^+e^- pairs created in pp, pn and pd collisions at intermediate energies. It is demonstrated that the proposed new observable, the dilepton decay anisotropy, quite sensitively changes for different sources and may be useful for their disentangling. The relevance of the dilepton decay anisotropy is shown in the context of a puzzling energy behavior for the ratio of the lepton yield from pd to pp reactions as observed at the BEVALAC