We derive a non-perturbative equation for the large scale structure power spectrum of longwavelength modes. Thereby, we use an operator product expansion together with relations between the three-point function and power spectrum in the soft limit. The resulting equation encodes the coupling to ultraviolet (UV) modes in two time-dependent coefficients, which may be obtained from response functions to (anisotropic) parameters, such as spatial curvature, in a modified cosmology. We argue that both depend weakly on fluctuations deep in the UV. As a byproduct, this implies that the renormalized leading order coefficient(s) in the effective field theory (EFT) of large scale structures receive most of their contribution from modes close to the non-linear scale. Consequently, the UV dependence found in explicit computations within standard perturbation theory stems mostly from counter-term(s). We confront a simplified version of our non-perturbative equation against existent numerical simulations, and find good agreement within the expected uncertainties. Our approach can in principle be used to precisely infer the relevance of the leading order EFT coefficient(s) using small volume simulations in an 'anisotropic separate universe' framework. Our results suggest that the importance of these coefficient(s) is a ∼ 10% effect, and plausibly smaller.
Introduction and SummaryThe measurement of anisotropies in the cosmic microwave background (CMB) by the Planck collaboration has provided invaluable information about the origin of the seed of structure [1], plausibly created during an early phase of accelerated expansion [2]. While this is a remarkable achievement, many questions still remain open regarding the nature of an inflationary cosmology.Perhaps the most outstanding one is whether a slowly-rolling, weakly coupled, fundamental scalar field played the role of the Higgs mechanism for the early universe; or if the universe chose a different path, such as dynamics at strong coupling or supersymmetry, e.g. [3][4][5]. These possibilities remain viable candidates to play a role in the early universe, and have not been considerably hindered by the Planck data [3]. In particular, the existent bounds on (equilateral) non-Gaussianity [6] are still above some well-motivated thresholds [3,7].Large-scale structure (LSS) surveys are due to become the next leading probe for precision cosmology, providing new information about the history of the universe through ambitious observational programs, currently under way to make very precise measurements. Therefore, the analytic control for the largest number of modes in the process of structure formation will allow us to place better constraints on cosmological parameters, and to further our understanding on the seed of structure. Unfortunately, quantitative predictions even for the simplest of the cosmologies is a daunting task, due to the non-linear nature of dark matter clustering. Moreover, even if one adopts a numerical approach, including baryonic matter is far from straightforward.He...