Should central banks buy equities and corporate bonds?

The coronavirus crisis once again give s rise to a major problem for monetary policies: in the event of a crisis or recession, monetary policy becomes expansionary, but the fall in share prices and the rise in credit spreads have a negative effect on the economy that may outweigh the positive effect of monetary policy; this positive effect is therefore lost because of the decline in financial wealth (equities and corporate bonds). A central bank must maintain an efficient functioning of monetary policy and an efficient transmission of monetary policy to the economy (this has been repeated recently by Philip Lane for the ECB). However, the fall in share prices and the widening of credit spreads prevent efficient monetary policy transmission since they slow down the economy at a time when monetary policy is trying to stimulate it. This leads us to believe that it would be legitimate, even without going outside their mandate, for central banks to buy equities (like the Bank of Japan) and corporate bonds, the motivation being to prevent the deterioration in the markets for these assets from eliminating the positive effect of monetary policy on the economy .