arXiv subjects
Publications and source records attributed to Res Urech.
The low energy scattering of pions is investigated in the presence of electromagnetic interactions at leading order and at next-to-leading order for the amplitudes involving at most one pair of charged pions. The size of the electromagnetic corrections to the S-wave scattering lengths is found to be comparable to the size of the two loop strong interaction corrections.
The effective chiral Lagrangian of the strong and electromagnetic interactions of the pseudoscalar mesons at low energies depends on a set of low energy constants. We determine the contributions to the electromagnetic coupling constants at order $O(e^2 p^2)$, which arise from resonances within a photon loop. We give some implications of our results, in particular we discuss in detail the effects on the corrections to Dashen's theorem.
Isospin violating signals in the tau -> 3 pi nu_tau decay mode are discussed. For the tau -> pi^- pi^- pi^+ nu_tau decay mode, isospin violation arises from the vector current contribution in the tau -> omega pi nu_tau decay with the subsequent isospin violating omega decay into pi^+ pi^-. We demonstrate that such effects may be observed in presently available data through the measurement of the interference effects of these vector current contributions with the dominating axial vector current, i.e. through a measurement of the structure functions W_F,W_G,W_H and W_I. In the case of the tau -> pi^0 pi^0 pi^- nu_tau decay mode, a vector current contribution is generated by eta pi mixing in the decay chain tau -> eta rho nu_tau -> pi^0 pi^0 pi^- nu_tau. We find that this effect is rather small, the magnitude of the associated interference terms being too low for present statistics.
We review a variety of topics related to hadronic structure functions in exclusive semihadronic tau decays. We introduce the concept of structure functions and summarize the most important concepts. We then calculate the decay $τ\to 3 πν_τ$ for very small hadronic invariant mass to one loop in Chiral Perturbation Theory. New interesting features emerge with respect to the known results at tree level, in particular for the structure functions $w_D$ and $w_E$. We discuss the prospects for experimental verification of our predictions. Finally, we discuss various issues at higher $Q^2$, related to hadronic resonance physics. Here we consider $2π$, $πK$, $3 π$, $K πK$ and $πK π$ hadronic final states.
The electromagnetic corrections to the masses of the pseudoscalar mesons $π$ and $K$ are considered. We calculate in chiral perturbation theory the contributions which arise from resonances within a photon loop at order $O(e^2 m_q)$. Within this approach we find rather moderate deviations to Dashen's theorem.
We construct an effective Lagrangian for the hadronic decays of a heavy excited $s$-wave-spin-one quarkonium into its ground state. We show that reasonable fits to the measured invariant mass spectra in the $J/ψ$ and $Υ$ systems can be obtained working in the chiral limit. The mass dependence of the various terms in the Lagrangian is discussed on the basis of a quark model.
In order to calculate the rho - omega mixing we extend the chiral couplings of the low-lying vector mesons in chiral perturbation theory to a lagrangian that contains two vector fields. We determine the momentum dependence of the two-point function and recover an earlier result for the on-shell expression. We discuss the off-shell behaviour of the mixing.