Higher spin gauge theory on fuzzy $S^4_N$

Abstract: We examine in detail the higher spin fields which arise on the basic fuzzy sphere $S^4_N$ in the semi-classical limit. The space of functions can be identified with functions on classical $S^4$ taking values in a higher spin algebra associated to $\mathfrak{so}(5)$. We derive an explicit and complete classification of the scalars and one-forms on the semi-classical limit of $S_N^4$. The resulting kinematics is reminiscent of Vasiliev theory. Yang-Mills matrix models naturally provide an action formulation for higher spin gauge theory on $S^4$, with 4 irreducible modes for each spin $s\geq 1$. We diagonalize the quadratic part of the effective action and exactly evaluate the quadratic part in the spin 2 sector. By identifying the linear perturbation of the effective metric, we obtain the exact kinetic term for all graviton candidates. At the classical level, matter $T_{\mu\nu}$ leads to three different contributions to the linearized metric: one consistent with linearized GR, one more rapidly decreasing contribution, and one non-propagating contribution localized at $T_{\mu\nu}$. The latter is too large to be physically acceptable, unless there is a significant induced quantum action. This issue should be resolved on generalized fuzzy spaces.