The supply side of the economy is beyond the orbit of monetary policy and, as a consequence, it is not realistic to expect that monetary policy can shape the long run growth rate of the economy. For this, different types of policies are required, such as those which affect incentives for private investment or the quality of the labour force.
Fiscal policy is far more important for the supply side of the economy than is monetary policy. What does this mean for the mandate of the central bank? The central bank should have clearly defined policy goals which it can realistically be expected to deliver, given the monetary policy tools it has at its disposal.