the LSS, both already operating, such as the DES [@Abbott:2005b] and also about to be commissioned in the next decade, like DESI [@Levi:2013gra], Euclid [@Laureijs:2011gra], the LSST [@Abell:2009aa] and WFIRST [@Spergel:2013tha], will provide us with particularly precise maps of the LSS that will shed light on the mysterious nature of the dark sector. Taking full advantage of this wealth of cosmological information poses a great challenge for experiment and theory alike.

From a theoretical standpoint, models of structure formation rely upon accurately tracing the nonlinear evolution of dark matter perturbations. In the linear regime and when gravity is governed by GR, different modes evolve independently, with the time evolution encapsulated in the scale-independent growth factor. At nonlinear scales, however, the dynamics of the self-gravitating dark matter system can only be tracked accurately by full-blown N-body simulations, which are highly computationally expensive . Additional complexity arises in accounting for the fact that the observed galaxies do not perfectly trace the underlying dark matter density field, but are biased tracers of it [@1984ApJ...284L...9K]. While this effect can be easily captured by introducing a multiplicative bias factor in the large scales [@1988MNRAS.235..715E], in the regime of nonlinear dynamics, empirical modeling needs to be 