How can a central bank become even more unconventional?

Central banks, in particular the ECB, wonder how they might react if the economic situation deteriorated: Policy interest rates are already low; Given the starting point of long-term interest rates, buying bonds under a new quantitative easing programme would have very little effect. This raises the question for central banks whether they should adopt an even more unconventional monetary policy than quantitative easing. What would an even more unconventional monetary policy entail ? Helicopter money is, in reality, equivalent to quantitative easing when the central bank never reduces the size of its balance sheet; The central bank c ould buy equities and High Yield bonds (to directly reduce companies’ borrowing costs); it could also buy bank loans (which would be complicated by the absence of market prices).