Glueballs and Their Kaluza-Klein Cousins

Spectra of glueball masses in non-supersymmetric Yang-Mills theory in three and four dimensions have recently been computed using the conjectured duality between superstring theory and large N gauge theory. The Kaluza-Klein states of supergravity do not correspond to any states in the Yang-Mills theory and therefore should decouple in the continuum limit. On the other hand, in the supergravity limit g_{YM}^2 N -> \infty, we find that the masses of the Kaluza-Klein states are comparable to those of the glueballs. We also show that the leading (g_{YM}^2N)^{-1} corrections do not make these states heavier than the glueballs. Therefore, the decoupling of the Kaluza-Klein states is not evident to this order.