Coarse graining $\pi\pi$ scattering

TL;DR

This paper analyzes $$ scattering in multiple channels up to 1.4 GeV using a coarse-grained approach that combines chiral dynamics and delta-shell potentials, ensuring proper analytic structure and fitting experimental data with minimal parameters.

Contribution

It introduces a novel coarse-grained framework for $$ scattering that combines long-range chiral interactions with short-range delta-shell potentials, maintaining analytic consistency.

Findings

Successfully describes scattering data with few parameters

Demonstrates the validity of coarse graining in hadronic physics

Addresses renormalization and crossing symmetry in the model

Abstract

We carry out an analysis of $\pi\pi$ scattering in the $IJ=00$, $11$ and $20$ channels in configuration space up to a maximal center-of-mass energy $\sqrt{s}=1.4$ GeV. We separate the interaction into two regions marked by an elementarity radius of the system; namely, a long distance region above which pions can be assumed to interact as elementary particles and a short distance region where many physical effects cannot be disentangled. The long distance interaction is described by chiral dynamics, where a two-pion-exchange potential is identified, computed and compared to lattice calculations. The short distance piece corresponds to a coarse grained description exemplified by a superposition of delta-shell potentials sampling the interaction with the minimal wavelength. We show how the so constructed non-perturbative scattering amplitude complies with the proper analytic structure, allowing for an explicit N/D type decomposition in terms of the corresponding Jost functions and fulfilling dispersion relations without subtractions. We also address renormalization issues in coordinate space and investigate the role of crossing when fitting the scattering amplitudes above and below threshold to Roy-equation results. At higher energies, we show how inelasticities can be described by one single complex and energy dependent parameter. A successful description of the data can be achieved with a minimal number of fitting parameters, suggesting that coarse graining is a viable approach to analyze hadronic processes.