Vector meson dominance and the pi^0 transition form factor

It is shown that the pi^0 transition form factor F(Q_1^2,Q_2^2) differs substantially from its one-real-photon limit F(Q_1^2,0) even for rather small values of Q_2^2 (approx 0.1 GeV^2), which cannot be excluded in experiments with one "untagged" electron. It indicates that the comparison of data with theoretical calculations, which usually assume Q_2^2=0, may be untrustworthy. Our phenomenological model of the pi^0 transition form factor is based on the vector-meson-dominance hypothesis and all its parameters are fixed by using the experimental data on the decays of vector mesons. The model soundness is checked in the two-real-photon limit, where it provides a good parameter-free description of the pi^0 -> 2 gamma decay rate, and in the pi^0 Dalitz decay. The dependence of F(Q_1^2,Q_2^2) on Q_1^2 at several fixed values of Q_2^2 is presented and the comparison with existing data performed.Comment: A slightly abbreviated version has been published as a Brief Report in Physical Review

Matter-induced hadronic processes

Two examples of ``exotic'' phenomena which become possible and important in the presence of nuclear matter are discussed: omega -> pi pi decay, and rho-omega mixing. Significance of these processes for the low-mass dilepton production in relativistic heavy-ion collisions is indicated.Comment: 8 pages, uses aipproc.cls, talk presented by W. Florkowski at the International Workshop on Hadron Physics "Effective Theories of Low Energy QCD", Coimbra, Portugal, September 10-15, 199

Strange particle production in a single-freeze-out model

The transverse-momentum spectra and elliptic flow of strange particles are calculated in the framework of the single-freeze-out model and compared with the recent RHIC data. An overall very good agreement between the model predictions and the data is obtained.Comment: talk presented by WF during the VIIIth Int. Conf. on Strangeness in Quark Matter, Cape Town, Sept. 15-20, 200

Response of nucleons to external probes in hedgehog models: I. Electromagnetic polarizabilities

Electromagnetic polarizabilities of the nucleon are analyzed in a hedgehog model with quark and meson degrees of freedom.Comment: 27 pages, DOE/ER/40322-155, U. of MD PP \#92-193, (ReVTeX

Vector and axial-vector correlators in a nonlocal chiral quark model

The behavior of nonperturbative parts of the isovector-vector and isovector and isosinglet axial-vector correlators at Euclidean momenta is studied in the framework of a covariant chiral quark model with nonlocal quark-quark interactions. The gauge covariance is ensured with the help of the P-exponents, with the corresponding modification of the quark-current interaction vertices taken into account. The low- and high-momentum behavior of the correlators is compared with the chiral perturbation theory and with the QCD operator product expansion, respectively. The V-A combination of the correlators obtained in the model reproduces quantitatively the ALEPH data on hadronic \tau decays, transformed into the Euclidean domain via dispersion relations. The predictions for the electromagnetic \pi^\pm - \pi^0 mass difference and for the pion electric polarizability are also in agreement with the experimental values. The topological susceptibility of the vacuum is evaluated as a function of the momentum, and its first moment is predicted to be \chi'(0)\approx (50 MeV)^2. In addition, the fulfillment of the Crewther theorem is demonstrated.Comment: 24 pages, 14 figures, LaTex (revised version

Hydrodynamics and perfect fluids: uniform description of soft observables in Au+Au collisions at RHIC

It is argued that the use of the initial Gaussian energy density profile for hydrodynamics leads to much better uniform description of the RHIC heavy-ion data than the use of the standard initial condition obtained from the Glauber model. With the modified Gaussian initial conditions we successfully reproduce the transverse-momentum spectra, v2, and the pionic HBT radii (including their azimuthal dependence). The emerging consistent picture of hadron production hints that a solution of the long standing RHIC HBT puzzle has been found.Comment: Talk presented by WF at the XXXVIII International Symposium on Multiparticle Physic

Vanishing dynamical quark mass at zero virtuality?

We show that the dynamical quark mass in effective nonlocal models can vanish at zero virtuality of the quark as $M(p^2)\propto p^2$. Our arguments follow from the constrained-instanton model of the QCD vacuum and from QCD sum rules calculations with nonlocal condensates. The discussed models also lead to analyticity of $M(p^2)$ in the vicinity of zero.Comment: 9 pages, Latex, 3 figure