Could Sample Variance be Responsible for the Parity-Violating Signal Seen in the BOSS Galaxy Survey?

Abstract

Recent works have uncovered an excess signal in the parity-odd four-point correlation function measured from the BOSS spectroscopic galaxy survey. If physical in origin, this could indicate evidence for new parity-breaking processes in the scalar sector, most likely from inflation. At heart, these studies compare the observed four-point correlator to 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 + LOWZ parity-odd dataset with the noise distribution modeled using the newly developed GLAM-Uchuu suite of mocks. These comprise full N-body simulations that follow the evolution of $2000^3$ dark matter particles in a $\Lambda$CDM universe, and represent a significant upgrade compared to the formerly MultiDark-Patchy mocks, which were based on an alternative (non N-body) gravity solver. We find no significant evidence for parity-violation in the BOSS dataset (with a baseline detection significance of $1.4\sigma$), suggesting that the former signal ($>3.5\sigma$ 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 catalogs showcases the heightened sensitivity of beyond-two-point analyses to the treatment of non-linear effects and indicates that previous constraints may suffer from large systematic uncertainties.