Fluctuation dissipation ratio in the one-dimensional kinetic Ising model

The exact relation between the response function R(t,t^') and the two time correlation function C(t,t^') is derived analytically in the one-dimensional kinetic Ising model subjected to a temperature quench. The fluctuation dissipation ratio X(t,t^') is found to depend on time through C(t,t^') in the time region where scaling C(t,t^')=f(t/t^') holds. The crossover from the nontrivial form X[C(t,t^')] to X(t,t^')≡1 takes place as the waiting time tw is increased from below to above the equilibration time teq.