Res Urech

Virtual Photons in Low Energy π − π Scattering

Abstract 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.

tau decays and chiral perturbation theory.

In a small window of phase space, chiral perturbation theory can be used to make standard model predictions for

ϱ0 - ω mixing in chiral perturbation theory

\ensuremath{\tau}

Resonance contributions to the electromagnetic low energy constants of chiral perturbation theory

decays into two and three pions. For

Corrections to Dashen's theorem.

\ensuremath{\tau}\ensuremath{\rightarrow}2\ensuremath{\pi}{\ensuremath{\nu}}_{\ensuremath{\tau}}

On the corrections to Dashen's theorem

, we give the analytical result for the relevant form factor

Structure functions in semihadronic Tau decays

{F}_{V}

Isospin violation in τ → 3πντ

up to two loops, then calculate the differential spectrum and compare with available data. For

Hadronic decays of excited heavy quarkonia

\ensuremath{\tau}\ensuremath{\rightarrow}3\ensuremath{\pi}{\ensuremath{\nu}}_{\ensuremath{\tau}}

Isospin violation in

, we have calculated the hadronic matrix element to one loop. We discuss the decomposition of the three pion states into partition states and we give detailed predictions for the decay in terms of structure functions. We also compare with low energy predictions of meson dominance models. Overall, we find good agreement, but also some interesting discrepancies, which might have consequences beyond the limit of validity of chiral perturbation theory.