MS. BASUNDHARA GHOSH

Future galaxy clustering surveys will probe small scales where nonlinearities become important. Having a very precise model at such scales is important especially in the context of discriminating alternative cosmological models from the standard one. In the mildly non-linear regime, such models typically differ little from each other, but galaxy clustering data will also be more and more precise in the near future. Since the observable quantity is angular power spectrum in redshift space, it is important to study the effect of nonlinear density and RSD terms on angular power spectrum. We compute one-loop contributions to the angular power spectrum using a flat-sky approximation that we introduce in this work, and compare our results in case of different perturbation approaches.