Abstract
We calculate the low-lying spectra for the positive-parity $\Delta$ and $N$ at two pion masses of 358 and 278 MeV using an isotropic clover action with two degenerate light-quaark and one strange-quark flavors through the application of the generalized variational method within the distillation framework. The spectrum exhibits the general features observed in previous calculations using an anisotropic clover lattice, with a counting of states at least as rich as the quark model. Furthermore, we identify states that are hybrid in nature, where gluonic degrees of freedom play a structural role, indicatinng that such states appear a feature of the excited baryon spectrum, irrespective of the lattice action, or the precise details of the smearing of the lattice interpolating operators used to identify such states.
Highlights
Lattice QCD provides a powerful numerical approach to solve QCD from the first principles, and has been successfully applied to address a range of key quantities in highenergy and nuclear physics, from the calculation of the ground-state spectrum, to nuclear charges and key measures of hadron structure
Symmetry, and the smaller spatial lattice spacing than that used in comparable studies using an anisotropic lattice
The higher excited states are displaced for clarity
Summary
The starting point for a study of the excited-state spectrum from lattice QCD is the extraction of the discrete, low-lying energy levels on the Euclidean lattice where lattice QCD is formulated. The most straightforward, albeit naïve, approach is to identify those energy levels with the single or multiparticle states in the spectrum. Whilst the resulting energy spectrum should be independent of the basis of interpolating operators employed, it has the potential to be highly sensitive to that basis. The first attempts to compute the spectrum employed baryon interpolating operators with a straightforward three-quark structure, mirroring the valence structure [1,2,3,4,5,6,7,8,9,10]
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