Colliding Ghosts: Constraining Inflation with the Parity-Odd Galaxy Four-Point Function

TL;DR

This paper uses galaxy data to test for parity-violation from inflationary models, finding no evidence and setting constraints on model parameters, thus challenging previous hints of parity-violation in galaxy distributions.

Contribution

First observational constraints on parity-violating inflationary models using galaxy four-point functions, including Cosmological Collider signatures, with systematic EFT analysis of late-time effects.

Findings

No significant parity-violation detected in galaxy data

Placed first constraints on coupling strengths of 18 inflationary models

Disfavors the hypothesis that galaxy parity-violation hints are due to new physics

Abstract

Could new physics break the mirror symmetry of the Universe? Utilizing recent measurements of the parity-odd four-point correlation function of BOSS galaxies, we probe the physics of inflation by placing constraints on the amplitude of a number of parity-violating models. Within canonical models of (single-field, slow-roll) inflation, no parity-asymmetry can occur; however, it has recently been shown that breaking of the standard assumptions can lead to parity violation within the Effective Field Theory of Inflation (EFTI). In particular, we consider the Ghost Condensate and Cosmological Collider scenarios -- the former for the leading and subleading operators in the EFTI and the latter for different values of mass and speed of an exchanged spin-$1$ particle -- for a total of $18$ models. Each instance yields a definite prediction for the inflationary trispectrum, which we convert to a late-time galaxy correlator prediction (through a highly non-trivial calculation) and constrain using the observed data. We find no evidence for inflationary parity-violation (with each of the $18$ models having significances below $2\sigma$), and place the first constraints on the relevant coupling strengths, at a level comparable with the theoretical perturbativity bounds. This is also the first time Cosmological Collider signatures have directly been searched for in observational data. We further show that possible secondary parity-violating signatures in galaxy clustering can be systematically described within the Effective Field Theory of Large-Scale Structure. We argue that these late-time contributions are subdominant compared to the primordial parity-odd signal for a vast region of parameter space. In summary, the results of this paper disfavor the notion that the recent hints of parity-violation observed in the distribution of galaxies are due to new physics.