Could sample variance be responsible for the parity-violating signal seen in the Baryon Oscillation Spectroscopic...

Recent works have uncovered an excess signal in the parity-odd four-point correlation function measured from the Baryon Oscillation Spectroscopic Survey (BOSS) galaxy catalogue. If physical in origin, this could indicate new parity-breaking processes in inflation. At heart, these studies compare the observed four-point correlator with the distribution obtained from parity-conserving mock galaxy surveys; if the simulations underestimate the covariance of the data, noise fluctuations may be misinterpreted as a signal. To test this, we reanalyse the BOSS CMASS parity-odd dataset with the noise distribution model using the newly developed GLAM-Uchuu suite of mocks. These comprise full [Formula: see text]-body simulations that follow the evolution of [Formula: see text] dark matter particles and represent a significant upgrade compared with the formerly used MultiDark-Patchy mocks, which were based on an alternative (non [Formula: see text]-body) gravity solver. We find no significant evidence for parity-violation (with a baseline detection significance of [Formula: see text]), suggesting that the former signal ([Formula: see text] with our data cuts) could be caused by an underestimation of the covariance in MultiDark-Patchy. The significant differences between results obtained with the two sets of BOSS-calibrated galaxy catalogues (whose covariances differ at the [Formula: see text] level) showcase the heightened sensitivity of beyond-two-point analyses to nonlinear effects and indicate that previous constraints may suffer from large systematic uncertainties.This article is part of the discussion meeting issue 'Challenging the standard cosmological model'.