Aspects of Chiral Dynamics
I discuss several topics in chiral perturbation theory - in particular, I recall pecularities of the chiral expansion in the baryon sector.
hep-ph↗
arXiv subjects
J. Gasser
Publications and source records attributed to J. Gasser.
Pion-pion scattering at low energy
We present technical details of the evaluation of the elastic pi-pi scattering amplitude to two loops in chiral perturbation theory. In particular, we elaborate on the renormalization procedure at the two-loop order and on the evaluation of the relevant Feynman diagrams that can all be expressed in terms of elementary functions. For the sake of clarity, we discuss these matters both in the N-component $ϕ^4$ theory (in its symmetric phase) and in chiral perturbation theory. Estimates for the relevant low-energy constants of $O(p^6)$ are presented. Threshold parameters and phase shifts are then calculated for two sets of $O(p^4)$ coupling constants and compared with experiment. We comment on the extraction of threshold parameters from phase shift data.
hep-ph↗
Elastic $ππ$ scattering to two loops
We evaluate analytically the elastic $ππ$ scattering amplitude to two loops in chiral perturbation theory and give numerical values for the two $S$--wave scattering lengths and for the phase shift difference $δ_0^0-δ_1^1$.
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The $ππ$ scattering amplitude in chiral perturbation theory
We discuss $ππ$ scattering in the framework of chiral perturbation theory. In particular, we recall the predictions made some time ago for the threshold parameters and for the phase shift difference $δ_0^0-δ_1^1$.
hep-ph↗
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↗
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.
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$K_{l4}$ - Decays Beyond One Loop
The matrix elements for $K\rightarrow ππłν$ decays are described by four form factors $F,G,H$ and $R$. We complete previous calculations by evaluating $R$ at next-to-leading order in the low-energy expansion. We then estimate higher order contributions using dispersion relations and determine the low-energy constants $L_1,L_2$ and $L_3$ from data on $K_{e4}$ decays and on elastic pion scattering. Finally, we present predictions for the slope of the form factor $G$ and for total decay rates.
hep-ph↗
Low-Energy Photon-Photon Collisions to Two-Loop Order
We evaluate the amplitude for $γγ\rightarrow π^0 π^0$ to two loops in chiral perturbation theory. The three new counterterms which enter at this order in the low-energy expansion are estimated with resonance saturation. We find that the cross section agrees rather well with the available data and with dispersion theoretic calculations even substantially above threshold. Numerical results for the Compton cross section and for the neutral pion polarizabilities are also given to two-loop accuracy.
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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↗
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↗