Information on the structure of the a1 from tau decay

Understand

The decay $\tau\to \pi\pi\pi\nu$ is analysed using different methods to account for the resonance structure, which is usually ascribed to the a1.

• One scenario is based on the recently developed techniques to generate axial-vector resonances dynamically, whereas in a second calculation the a1 is introduced as an explicit resonance.
• We investigate the influence of different assumptions on the result.
• In the molecule scenario the spectral function is described surprisingly well by adjusting only one free parameter.