How should we analyse the link between fiscal policy and monetary policy in an environment of very low interest rates?

Instead of thoughtlessly proposing increases in fiscal deficits since interest rates are low in OECD countries, the links between low interest rates and fiscal policies should be thoroughly analysed : The first question is what factor explains the low interest rates: does it guarantee that they will remain low for a long time? If the answer is no, it is not possible to switch to a more expansionary fiscal policy and to increase the public debt; If the answer is yes, we have to keep in mind that it is nevertheless not possible - even if interest rates are low – to finance current fiscal deficits by public borrowing ; these deficits do not generate the additional income that makes it possible to repay the public debt; But the virtue of low long-term interest rates is that they make it possible to finance, via the fiscal deficit, public investments whose efficiency and profitability are evident only in the long term (education, energy transition, R&D, financing of innovative companies, etc.). The reason is that if long-term interest rates are very low, future returns count as much as current returns, whereas if long-term interest rates are high, the discounted value of future returns is very low.