arXiv subjects
Publications and source records attributed to A. Gokalp.
We consider the two point correlation function of scalar current in QCD sum rules approach to estimate the overlap amplitude of $a_0$ meson. We then employ QCD sum rules to calculate the coupling constants g$_{ωa_0γ}$ and g$_{ρa_0γ}$ by studying the three point ${a_0ωγ}$- and ${a_0ργ}$-correlation functions.
We study the radiative decay $ϕ\toπ^{0}π^{0}γ$ within the framework of a phenomenological approach in which the contributions of $σ$-meson, $ρ$-meson and $f_0$-meson are considered. We analyze the interference effects between different contributions and utilizing the experimental branching ratio for this decay we estimate the coupling constant $g_{ϕσγ}$.
We employ QCD sum rules to calculate the coupling constant g$_{ρσγ}$ by studying the three point ${ρσγ}$-correlation function. Our results is consistent with the value of this coupling constant obtained using vector meson dominance of the electromagnetic current and the experimental $ρ^0$-photoproduction data.
We employ QCD sum rules to calculate the coupling constants g$_{ρπγ}$ and g$_{ωπγ}$ by studying the three point ${ρπγ}$- and ${ωπγ}$-correlation functions. Our results for the decay widths $Γ(ρ^0\to π^0γ)$ and $Γ(ω\to π^0γ)$ calculated using the obtained coupling constants are in good agreement with the experimental values of these decay widths.
Collisional damping widths of giant monopole and quadrupole excitations for $^{120}$Sn and $^{208}$Pb at zero and finite temperatures are calculated within Thomas-Fermi approximation by employing the microscopic in-medium cross-sections of Li and Machleidt and the phenomenological Skyrme and Gogny forces, and are compared with each other. The results for the collisional widths of giant monopole and quadrupole vibrations at zero temperature as a function of the mass number show that the collisional damping of giant monopole vibrations accounts for about 30-40% of the observed widths at zero temperature, while for giant quadrupole vibrations it accounts for only 20-30% of the observed widths of zero temperature.
We study the radiative decay $ρ^{0}\toπ^{0}π^{0}γ$ within the framework of a phenomenological approach in which the contributions of $σ$-meson and $ω$-meson intermediate states and of the pion-loops are considered. We conclude that the $σ$-meson amplitude provides the dominant contribution.
We study the $ω\toππγ$ decays by adding to the amplitude calculated within the framework of chiral perturbation theory and vector meson dominance the amplitude of $σ$-meson intermediate state. We estimate the coupling constant $g_{ωσγ}$ utilizing the experimental value of the $ω\toπ^{0}π^{0}γ$ decay rate.
The experimental branching ratio for the radiative decay $ρ^{0}\toπ^{+}+π^{-}+γ$ is used to estimate the coupling constant $g_{ρσγ}$ for a set of values of $σ$-meson parameters M$_σ$ and $Γ_σ$. Our results are quite different than the values of this constant used in the literature.
We employ the light cone QCD sum rules to calculate $ΔπN$ coupling constant by studying the two point correlation function between the vacuum and the pion state. Our result is consistent with the traditional QCD sum rules calculations and it is in agreement with the experimental value.
A detailed derivation of the collisional widths of collective vibrations is presented in both quantal and semi-classical frameworks by considering the linearized limits of the extended TDHF and the BUU model with a non-Markovian binary collision term. Damping widths of giant dipole and giant quadrupole excitations are calculated by employing an effective Skyrme force, and the results are compared with GDR measurements in Lead and Tin nuclei at finite temperature.