Spectral Analysis of Spatial-Sign Covariance Matrices with Dependence and Weaker Moment Conditions

This paper investigates the spectral properties of spatial-sign covariance matrices, a self-normalized version of sample covariance matrices, for data from alpha-regularly varying populations with general covariance structures. By exploiting the elegant properties of self-normalized random variables, we establish the limiting spectral distribution and a central limit theorem for linear spectral statistics. We demonstrate that the Marcenko-Pastur equation holds under the condition alpha >= 2, while the central limit theorem for linear spectral statistics is valid for alpha > 4, which are shown to be nearly the weakest possible conditions for spatial-sign covariance matrices from heavy-tailed data in the presence of dependence.