$N\pi$ scattering in the Roper channel

TL;DR

This lattice QCD study investigates the Roper resonance in the nucleon channel, suggesting that coupled channel effects involving Nπ and Nππ are essential to reproduce the experimentally observed low-lying Roper state.

Contribution

The paper provides new lattice QCD results showing the importance of coupled channel effects in understanding the Roper resonance, which was not captured by elastic Nπ scattering alone.

Findings

Elastic Nπ scattering does not produce a low-lying Roper.

Coupled Nπ and Nππ channels are crucial for the Roper resonance.

Results support the Roper as a dynamically generated resonance.

Abstract

We present results from our recent lattice QCD study of $N\pi$ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance $N^*(1440)$ resides in experiment. Using a variety of hadron operators, that include $qqq$-like, $N\pi$ in $p$-wave and $N\sigma$ in $s$-wave, we systematically extract the excited lattice spectrum in the nucleon channel up to 1.65 GeV. Our lattice results indicate that N$\pi$ scattering in the elastic approximation alone does not describe a low-lying Roper. Coupled channel effects between $N\pi$ and $N\pi\pi$ seem to be crucial to render a low-lying Roper in experiment, reinforcing the notion that this state could be a dynamically generated resonance. After giving a brief motivation for studying the Roper channel and the relevant technical details to this study, we will discuss the results and the conclusions based on our lattice investigation and in comparison with other lattice calculations.