Energy decay for the linear Klein-Gordon equation and boundary control

In this work we study the asymptotic behavior of the solutions of the linear Klein-Gordon equation in RN, N⩾1. We prove that local energy of solutions to the Cauchy problem decays polynomially. Afterwards, we use the local decay of energy to study exact boundary controllability for the linear Klein-Gordon equation in general bounded domains of RN, N⩾1.