... in the Keynesian Growth framework, monetary policy expansions support investment spending and capital deepening by lowering the cost of credit and increasing the profitability of investing in future productive capacity. Empirical evidence presented by Aghion et al. (2018) and Moran and Queralto (2018) indicates that monetary policy expansions lead to higher investment in innovation and productivity growth.
... Monetary policy cannot always provide the necessary stimulus to stabilize the economy during a recession—for instance, because of the zero lower bound on interest rates. In such cases, our Keynesian Growth framework acknowledges that constraints on monetary policy incur long-term costs, which stem from a lower trajectory for trend productivity growth. In this context, the social losses from insufficient accommodation in the short term may get amplified by a long-term fall in potential output stemming from a lack of productivity-boosting investment spending. [Source]
Keynesianism in that case calls for fiscal stimulus.