Form Factors in the radiative pion decay

TL;DR

This paper analyzes the form factors governing the structure-dependent amplitude in radiative pion decay, constructing them through QCD principles and comparing with experimental data, while assessing the potential for New Physics detection.

Contribution

It introduces a method to construct vector and axial-vector form factors using QCD asymptotic properties and evaluates the role of a non-standard tensor form factor.

Findings

Resonance contributions to pion decay are computed.

Comparison shows current uncertainties hinder New Physics searches.

The non-standard tensor form factor has a limited impact.

Abstract

We perform an analysis of the form factors that rule the structure-dependent amplitude in the radiative pion decay. The resonance contributions to pion -> e nu_e gamma decays are computed through the proper construction of the vector and axial-vector form factors by setting the QCD driven asymptotic properties of the three-point Green functions VVP and VAP, and by demanding the smoothing of the form factors at high transfer of momentum. A comparison between theoretical and experimental determinations of the form factors is also carried out. We also consider and evaluate the role played by a non-standard tensor form factor. We conclude that, at present and due to the hadronic incertitudes, the search for New Physics in this process is not feasible.