Meson-Glueball Mixing and Other Back-Reaction Effects in the Sakai-Sugimoto Model of AdS/QCD

Top-down holographic QCD models often work in the probe approximation (also known as the quenched approximation), assuming that the number of colors is much greater than the number of flavors. Going beyond this approximation is essential to a fuller understanding of holography and more accurate phenomenological predictions. Even as multiple works venture to study particle mass spectra with some back-reaction effects included, meson-glueball mixing is a key effect in the quadratic order Lagrangian that has so far been largely neglected in the literature -- and aligns with phenomenological hypotheses that many low-lying meson states are in fact part glueball. In this talk, we describe the mixing between vector glueballs and scalar mesons arising from the DBI action in the Sakai-Sugimoto model of holographic QCD, and show that this mixing must be treated as a part of the back-reaction of the D8-branes onto the background geometry. Including this back-reaction with the simplification that it is ``smeared out'' over the compact transverse direction, we analyze first order corrections to the mass spectra of both the vector and scalar particles. We show that while the vector glueball masses are unaffected by the explicit mixing, this effect is the most significant back-reaction correction to the masses of low-lying scalar mesons.