Extracting New Physics from the CMB

TL;DR

This work investigates whether transplanckian (Planck-scale) physics can leave observable imprints in the cosmic microwave background via initial-state modifications. It develops and contrasts two theoretical formalisms—boundary Effective Field Theory (EFT) on a fixed initial-time surface and New Physics Hypersurface (NPH) with near-scale-invariant initial data—both predicting an oscillatory modulation of the primordial power spectrum $P(k)$. The key results are explicit expressions for the corrections in each framework, showing how the oscillation amplitude and period depend on the ratio $H/M$ and the relevant scales, and how these patterns can be used to distinguish the two scenarios using current or future CMB data. The findings indicate that, provided $H/M$ is sufficiently large (roughly $\gtrsim 10^{-3}$), these oscillatory signatures could offer a direct probe of Planck-scale physics, with potential extensions to galaxy surveys and a path to constraining or measuring the new-physics scale $M$. Overall, the paper frames a phenomenological strategy to test transplanckian physics through precise measurements of the CMB power spectrum and its possible oscillatory features.

Abstract

We review how initial state effects generically yield an oscillatory component in the primordial power spectrum of inflationary density perturbations. These oscillatory corrections parametrize unknown new physics at a scale $M$ and are potentially observable if the ratio $H_{infl}/M$ is sufficiently large. We clarify to what extent present and future CMB data analysis can distinguish between the different proposals for initial state corrections.