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Abstract:

The standard inflationary model predicts that primordial perturbations are Gaussian random fields. For such fields the power spectrum (or equivalently, the two-point correlation function) serves as a sufficient statistic, which is why it plays a central role in cosmological analyses. However observables in the late-time universe exhibit significant non-Gaussianity due to nonlinear mode-coupling by gravity, making analyses based solely on the power spectrum potentially suboptimal. This naturally raises the question: how much information lies beyond the power spectrum? To address this I employ an optimal analysis technique, known as field-level inference. I demonstrate when and why the power spectrum becomes suboptimal and argue that a joint analysis using both the power spectrum and the bispectrum captures nearly all the information available through full field-level inference.