Operator Error Estimates for Homogenization of Hyperbolic Equations

A self-adjoint strongly elliptic second-order differential operator Aε on L2(ℝd;ℂn) is considered. It is assumed that the coefficients of Aε are periodic and depend on x/ε, where ε > 0 is a small parameter. Approximations for the operators cos(Aε1/2τ) and Aε1/2 sin(Aε1/2τ) in the norm of operators from the Sobolev space Hs(ℝd;ℂn) to L2(ℝd;ℂn) (for appropriate s) are obtained. Approximation with a corrector for the operator Aε1/2 sin(Aε1/2τ) in the (Hs → H1)-norm is also obtained. The question about the sharpness of the results with respect to the norm type and with respect to the dependence of the estimates on is studied. The results are applied to study the behavior of the solutions of the Cauchy problem for the hyperbolic equation ∂τ2uε = − Aεuε.