arXiv subjects

G. Ecker

Publications and source records attributed to G. Ecker.

46 records · Page 3Linked to original sources

arXiv1994

Semileptonic Kaon Decays

We present the matrix elements for the semileptonic kaon decays $K_{l2γ}$ , $K_{l2l^+l^-}$, $K_{l2l'^+l'^-}$,$K_{l3}$, $K_{l3γ}$ and $K_{l4}$ at next-to-leading order, and $K_{e5}$ at leading order in Chiral Perturbation Theory and compare the predictions with experimental data. For $K_{l4}$ decays we estimate yet higher orders in order to reduce theoretical uncertainties in the comparison with the data. Monte Carlo event generators are used to calculate the corresponding rates at DA$Φ$NE. We discuss the possibilities to improve our knowledge of the low-energy structure of the Standard Model at this and similar machines.

hep-ph↗

arXiv1994

Chiral Perturbation Theory

An introduction to Chiral Perturbation Theory is given including a discussion of power counting, the Wess-Zumino term, the values of the coupling constants and the inclusion of the effects of other resonances.

hep-ph↗

arXiv1994

What is a low-energy theorem ?

We discuss the meaning of low-energy theorems (LETs) in the framework of the effective field theory of the standard model. Particular emphasis is put on the LET for neutral pion photoproduction off nucleons at threshold. The seemingly controversial situation surrounding this LET is clarified.

hep-ph↗

arXiv1994

The pion-nucleon interaction as an effective field theory

After a brief survey of effective field theories, the linear sigma model is discussed as a prototype of an effective field theory of the standard model below the chiral-symmetry-breaking scale. Although it can serve as a toy model for the pion-nucleon interaction, the linear sigma model is not a realistic alternative to chiral perturbation theory. The heavy-baryon approach to chiral perturbation theory allows for a systematic low-energy expansion of Green functions and amplitudes with baryons. The chiral-invariant renormalization of the effective field theory for the pion-nucleon system to O(p^3) in the chiral expansion is reviewed.

hep-ph↗

arXiv1994

Chiral invariant renormalization of the pion--nucleon interaction

The leading divergences of the generating functional for Green functions of quark currents between one--nucleon states are calculated with heat kernel techniques. The results allow for a chiral invariant renormalization of all two--nucleon Green functions of the pion--nucleon system to $O(p^3)$ in the low--energy expansion.

hep-ph↗

arXiv1993

The standard model at low energies

The hadronic sector of the standard model at low energies is described by a non--decoupling effective field theory, chiral perturbation theory. An introduction is given to the construction of effective chiral Lagrangians, both in the purely mesonic sector and with inclusion of baryons. The connection between the relativistic formulation and the heavy baryon approach to chiral perturbation theory with baryons is reviewed.

hep-ph↗

arXiv1993

Non-Leptonic Kaon Decays and the Chiral Anomaly

An investigation is performed of all non-leptonic kaon decays sensitive to the chiral anomaly. Within the framework of chiral perturbation theory, there are two classes of anomalous amplitudes at $O(p^4)$: reducible and direct contributions. Only radiative transitions are affected by the anomaly. The phenomenology of the decays $K_L \to π^+ π^- γ$ and $K^+ \to π^+ π^0 γ$ is studied in detail. Including the dominant contributions of $O(p^6)$, the experimentally observed dependence of the direct emission amplitude for $K_L \to π^+ π^- γ$ on the photon energy can be understood. A survey is made of the rare ``anomalous'' decays $K \to ππγγ$ and $K \to 3 πγ(γ)$, including some numerical estimates.

hep-ph↗

arXiv1992

Radiative Semileptonic Kaon Decays

We evaluate the matrix elements for the radiative kaon decays $K^+ \to l^+ν_lγ$, $l^+ ν_l l'^+ l'^-$ and $K \to πl ν_lγ$ \ ($l,\ l' = e,μ$) to next-to-leading order in chiral perturbation theory. We calculate total rates and rates with several kinematical cuts and confront the results with existing data. Measurements at future kaon facilities will allow for a more detailed comparison between theory and experiment.

hep-ph↗

arXiv1992

Semileptonic Kaon Decays in Chiral Perturbation Theory

We present the matrix elements for the semileptonic kaon decays $K_{l2γ}$, $K_{l2l^+l^-}$, $K_{l2l'^+l'^-}$, $K_{l3}$, $K_{l3γ}$ and $K_{l4}$ at next-to-leading order in chiral perturbation theory and compare the predictions with experimental data. Monte Carlo event generators are used to calculate the corresponding rates at DAFNE. We discuss the possibilities to improve our knowledge of the low-energy structure of the Standard Model at this and similar machines.

hep-ph↗

arXiv1992

The Chiral Anomaly in Non-Leptonic Weak Interactions

The interplay between the chiral anomaly and the non-leptonic weak Hamiltonian is studied. The structure of the corresponding effective Lagrangian of odd intrinsic parity is established. It is shown that the factorizable contributions (leading in $1/N_C$) to that Lagrangian can be calculated without free parameters. As a first application, the decay $K^+ \ra π^+ π^0 γ$ is investigated.

hep-ph↗