On asymptotics of eigenvectors of large sample covariance matrix

Z. D. Bai, B. Q. Miao, G. M. Pan

Let \{XijX_{ij}\}, i,j=...,i,j=..., be a double array of i.i.d. complex random variables with EX11=0,EX112=1EX_{11}=0,E|X_{11}|^2=1 and E|X_{11}|^4<\infty, and let An=1NTn1/2XnXnTn1/2A_n=\frac{1}{N}T_n^{{1}/{2}}X_nX_n^*T_n^{{1}/{2}}, where Tn1/2T_n^{{1}/{2}} is the square root of a nonnegative definite matrix TnT_n and XnX_n is the n×Nn\times N matrix of the upper-left corner of the double array. The matrix AnA_n can be considered as a sample covariance matrix of an i.i.d. sample from a population with mean zero and covariance matrix TnT_n, or as a multivariate FF matrix if TnT_n is the inverse of another sample covariance matrix. To investigate the limiting behavior of the eigenvectors of AnA_n, 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 \{XijX_{ij}\} and TnT_n are either real or complex and some additional moment assumptions are made then linear spectral statistics defined by the eigenvectors of AnA_n are proved to have Gaussian limits, which suggests that the eigenvector matrix of AnA_n is nearly Haar distributed when TnT_n is a multiple of the identity matrix, an easy consequence for a Wishart matrix.