Aging in ferromagnetic systems at criticality near four dimensions

We report on some results concerning the off-equilibrium response and correlation functions and the corresponding fluctuation-dissipation ratio for a purely dissipative relaxation of an O (N) symmetric vector model (Model A) in d dimensions below the upper critical dimension. The scaling behaviour of these quantities is analyzed and the associated universal functions are given at first order in epsilon=4 d in the high-temperature phase and at criticality. A non trivial limit of the fluctuation-dissipation ratio is found at criticality.