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Parity-violating physics in the early Universe can leave detectable traces inlate-time observables. Whilst vector- and tensor-type parity-violation can beobserved in the $B$-modes of the cosmic microwave background, scalar-typesignatures are visible only in the four-point correlation function (4PCF) andbeyond. This work presents a blind test for parity-violation in the 4PCF of theBOSS CMASS sample, considering galaxy separations in the range$[20,160]h^{-1}\mathrm{Mpc}$. The parity-odd 4PCF contains no contributionsfrom standard $\Lambda$CDM physics and can be efficiently measured usingrecently developed estimators. Data are analyzed using both a non-parametricrank test (comparing the BOSS 4PCFs to those of realistic simulations) and acompressed $\chi^2$ analysis, with the former avoiding the assumption of aGaussian likelihood. These find similar results, with the rank test giving adetection probability of $99.6\%$ ($2.9\sigma$). This provides significantevidence for parity-violation, either from cosmological sources or systematics.We perform a number of systematic tests: although these do not reveal anyobservational artefacts, we cannot exclude the possibility that our detectionis caused by the simulations not faithfully representing the statisticalproperties of the BOSS data. Our measurements can be used to constrain physicalmodels of parity-violation. As an example, we consider a coupling between theinflaton and a $U(1)$ gauge field and place bounds on the latter's energydensity, which are several orders of magnitude stronger than those previouslyreported. Upcoming probes such as DESI and Euclid will reveal whether ourdetection of parity-violation is due to new physics, and strengthen the boundson a variety of models.

Probing Parity-Violation with the Four-Point Correlation Function of BOSS Galaxies