Prepared for submission to JCAP The Bispectrum in the Effective Field Theory of Large Scale Structure

Abstract. We study the bispectrum in the Effective Field Theory of Large Scale Struc-ture, consistently accounting for the effects of short-scale dynamics. We begin by proving that, as long as the theory is perturbative, it can be formulated to arbitrary order us-ing only operators that are local in time. We then derive all the new operators required to cancel the UV-divergences and obtain a physically meaningful prediction for the one-loop bispectrum. In addition to new, subleading stochastic noises and the viscosity term needed for the one-loop power spectrum, we find three new effective operators. The three new parameters can be constrained by comparing with N-body simulations. The best fit is precisely what is suggested by the structure of UV-divergences, hence justifying a formula for the EFTofLSS bispectrum whose only fitting parameter is already fixed by the power spectrum. This result predicts the bispectrum of N-body simulations up to kmax ≈ 0.22hMpc−1 at z = 0, an improvement by nearly a factor of two as compared to one-loop standard perturbation theory. ar X i