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Robust inference with minimal dependence on uncertain models of physical processes is increasingly essential for precision cosmology. We present a geometrical test based on a null statistic constructed from the distribution of galaxies around cosmological voids and clusters of galaxies. The key idea is to form crossed density contrasts whose leading linear redshift-space distortion terms cancel, such that the quadrupole of the resulting combined correlation function vanishes when the redshifts of objects are translated to distances using the true cosmology. Using the cosmological geometry generates a non-zero quadrupole. Within the likelihood, the model quadrupole is always zero and no complicated modeling is required to make inferences, thus providing a particularly clean route to Alcock-Paczynski (AP) measurements. We use mock galaxy catalogs to demonstrate a practical implementation of the new statistic, measuring anisotropic AP distortions over the large scales relevant for geometric inference. Our new statistic is qualitatively distinct from traditional BAO analyses and offers an independent geometric test using the same data, providing both a complementary probe and a non-trivial consistency check of the distance-redshift relation.

BIO

Hanyu Zhang is a WCA postdoctoral fellow at University of Waterloo. He completed his Ph.D in physics at Kansas State University under the supervision of Dr. Lado Samushia. Hanyu is actively involved in the DESI collaboration, contributing to various key projects and working groups.

Host: Cheng Zhao