Signatures of very high energy physics in the squeezed limit of the bispectrum (violation of Maldacena's condition)
Diego Chialva
TL;DR
This work addresses how very high-energy physics can modify the squeezed limit of the primordial scalar bispectrum in single-field inflation. By employing the in-in formalism and a general effective action framework, it analyzes both modified dispersion relations and modified initial states (BEFT and NPHS), showing that these High-Energy modifications principally alter the Whightman functions, leading to particle-content, interference, and time-accumulation effects that enhance or reshape the squeezed bispectrum. The study provides general results valid for all cubic couplings, illustrates two detailed examples (minimal cubic and quartic derivative interactions), and derives scaling laws for the $k_1$-dependence across regimes defined by the relations between $k_1$, $k_S$, and the new-physics scale $\Lambda$ (or corresponding WKB times). It also discusses implications for halo bias and emphasizes that naive folded templates can mispredict the squeezed-limit behavior in these scenarios. Overall, the paper shows that precise measurements of large-scale structure could constrain or reveal the scale and nature of high-energy physics imprinted in primordial non-Gaussianities.
Abstract
We investigate the signatures in the squeezed limit of the primordial scalar bispectrum due to modifications of the standard theory at high energy. In particular, we consider the cases of modified dispersion relations and/or modified initial quantum state (both in the Boundary Effective Field Theory and in the New Physics Hyper-Surface formulations). Using the in-in formalism we study in details the squeezed limit of the contributions to the bispectrum from all possible cubic couplings in the effective theory of single-field inflation. We find general features such as enhancements and/or non-local shape of the non-Gaussianities, which are relevant, for example, for measurements of the halo bias and which distinguish these scenarios from the standard one (with Bunch-Davies vacuum as initial state and standard kinetic terms). We find that the signatures change according to the magnitude of the scale of new physics, and therefore several pieces of information regarding high energy physics could be obtained in case of detection of these signals, especially bounds on the scales of new physics.