# Edge universality of separable covariance matrices

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In this talk, we consider the largest singular value of the so-called separable covariance matrix Y=A^{1/2}XB^{1/2}, where X is a random matrix with i.i.d. entries and A, B are deterministic covariance matrices (which are non-negative definite symmetric). The separable covariance matrix is commonly used in e.g. environmental study, wireless communications and financial study to model sampling data with spatio-temporal correlations. However, the spectral properties of separable covariance matrices are much less known compared with sample covariance matrices.

Recently, we prove that the distribution of the largest singular value of Y converges to the Tracy-Widom law under the minimal moment assumption on the entries of X. This is the first edge universality result for separable covariance matrices. As a corollary, if B=I, we obtain the edge universality for sample covariance matrices with correlated data and heavy tails. This improves the previous results for sample covariance matrices, which usually assume diagonal A or high moments of the X entries. The core parts of the proof are two comparison arguments: the Lindeberg replacement method, and a continuous self-consistent comparison argument.