The concept of neutral interest rate makes no sense in an open economy with high international capital mobility

In a closed economy, the neutral interest rate clearly makes sense: it is the real interest rate that equalises savings and investment. But the neutral interest rate cannot be defined in an open economy with high international capital mobility . If international capital mobility is high, the country’s interest rate first necessarily depends on the interest rate in other countries. Second , if savings are not equal to investment, there is either an accumulation of external assets, or an accumulation of external debt, which can be completely acceptable if the marginal productivity of capital is different from that in other countries. So monetary policy cannot have the neutral interest rate as a reference in an open economy with high international capital mobility (as the euro zone or the United States).