Abstract
The origin of the low-lying position of the Roper resonance in the nucleon energy spectrum has been the subject of significant interest for many years, including several investigations using lattice QCD. It has been claimed that chiral symmetry plays an important role in our understanding of this resonance. We present results from our systematic examination of the potential role of chiral symmetry in the low-lying nucleon spectrum through the direct comparison of the clover and overlap fermion actions. After a brief summary of the background motivation, we specify the computational details of the study and outline our comparison methodologies. We do not find any evidence supporting the claim that chiral symmetry plays a significant role in understanding the Roper resonance on the lattice.
Highlights
Discovered in 1964 via a partial wave analysis of pion-nucleon scattering data [1], the Roper resonance (N(1440) +)has an unusually large full width lying resonance in the nucleon spectrum, sitting below of ≈350 the firstMeV [2] and is negative-parity the lowest- N(1535) −state
The χQCD Collaboration have seen a low mass, consistent with the Roper resonance. They emphasise their use of a lattice fermion action which respects chiral symmetry as being key to obtaining their result [14, 15]
It is important to note that the χQCD result is dependent on their use of the sequential empirical Bayes (SEB) analysis method [16]
Summary
Discovered in 1964 via a partial wave analysis of pion-nucleon scattering data [1], the Roper resonance (N(1440). The χQCD Collaboration have seen a low mass, consistent with the Roper resonance. They emphasise their use of a lattice fermion action which respects chiral symmetry as being key to obtaining their result [14, 15]. [14] that when the SEB algorithm is applied to the same correlation functions, produced with a lattice fermion action which does not respect chiral symmetry, the SEB analysis obtains a ground state mass in agreement with a correlation matrix analysis, but a lower first excited state mass. Fermion action which respects chiral symmetry, in comparison to a fermion action which does not Given these discrepancies, we aim to carefully assess the role chiral symmetry plays in understanding the Roper resonance on the lattice
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