Serguei Naboko, Sergey Simonov Spectral analysis of a class of hermitian Jacobi matrices in a critical (double root) hyperbolic case: periodically modulated matrix entries. (360K, postscript) ABSTRACT. We consider a class of Jacobi matrices with periodically modulated diagonal in a critical hyperbolic ("double root") situation. For the model with "non-smooth" matrix entries we obtain the asymptotics of generalized eigenvectors and analyze the spectrum of the corresponding Jacobi matrix.