Meson and Glueball Spectra in Holographic QCD*

In holographic QCD, mesons and glueballs are represented by “wavefunctions” satisfying eigenvalue equations in a higher dimensional space. Mesons are confined to a hypersurface in this space, while glueball wavefunctions can be located anywhere. The shape of the extra dimensions dictates the particles’ 4D mass spectrum. In one of the most famous holographic QCD models, the Witten-Sakai-Sugimoto model, these mass spectra are controlled by a single scale.

This presentation details how we found estimates for this mass scale in the Witten-Sakai-Sugimoto model for glueballs and mesons separately. We used PDG data for mesons, and lattice-simulation data for glueballs. We found significant disagreement between the meson and glueball estimates of the mass scale, and investigated a disagreement about the parity assignments of glueballs within holographic QCD. Our results suggest the presence of an additional scale in determining the meson spectrum, possibly related to the shape of the hypersurface the meson wavefunctions occupy.