United States, euro zone: How much has monetary policy contributed to the downward trend in real long-term interest rates?

In the United States and the euro zone, real long-term interest rates have declined as a trend under the effect of strong global demand for risk-free financial assets and the decline in potential growth. In addition to these structural factors, which explain the decline in real long-term interest rates , this decline has been amplified by expansionary monetary policies (very low short-term interest rates, quantitative easing, etc.). What contribution have monetary policies made to the decline in real long-term interest rates compared with the structural factors? We find that since 2011-2012 in the United States and the euro zone, the expansionary monetary policy has contributed to the decline in real long-term interest rates beyond what has resulted from the excess demand for risk-free assets and the decline in potential growth.