Spacetime Quotients, Penrose Limits and Conformal Symmetry Restoration
  In this paper we study the Penrose limit of AdS_5 orbifolds. The orbifold can be either in the pure spatial directions or space and time directions. For the AdS_5/\Gamma\times S^5 spatial orbifold we observe that after the Penrose limit we obtain the same result as the Penrose limit of AdS_5\times S^5/\Gamma. We identify the corresponding BMN operators in terms of operators of the gauge theory on R\times S^3/\Gamma. The semi-classical description of rotating strings in these backgrounds have also been studied. For the spatial AdS orbifold we show that in the quadratic order the obtained action for the fluctuations is the same as that in S^5 orbifold, however, the higher loop correction can distinguish between two cases. 
Mohsen Alishahiha, Mohammad M. Sheikh-Jabbari, Radu Tatar