On asymptotics of eigenvectors of large sample covariance matrix
Z. D. Bai, B. Q. Miao, G. M. Pan
Let \{\}, be a double array of i.i.d. complex random variables with and E|X_{11}|^4<\infty, and let , where is the square root of a nonnegative definite matrix and is the matrix of the upper-left corner of the double array. The matrix can be considered as a sample covariance matrix of an i.i.d. sample from a population with mean zero and covariance matrix , or as a multivariate matrix if is the inverse of another sample covariance matrix. To investigate the limiting behavior of the eigenvectors of , a new form of empirical spectral distribution is defined with weights defined by eigenvectors and it is then shown that this has the same limiting spectral distribution as the empirical spectral distribution defined by equal weights. Moreover, if \{\} and are either real or complex and some additional moment assumptions are made then linear spectral statistics defined by the eigenvectors of are proved to have Gaussian limits, which suggests that the eigenvector matrix of is nearly Haar distributed when is a multiple of the identity matrix, an easy consequence for a Wishart matrix.