We obtain exact expressions for the two-time autocorrelation and response
functions of the d-dimensional linear Glauber model. Although this linear
model does not obey detailed balance in dimensions d≥2, we show that the
usual form of the fluctuation-dissipation ratio still holds in the stationary
regime. In the transient regime, we show the occurence of aging, with a special
limit of the fluctuation-dissipation ratio, X∞=1/2, for a quench at
the critical point.Comment: Accepted for publication (Physical Review E