First, there is the effect through the aforementioned risk premium, which focuses on supply and demand in asset markets. This effect is called the “portfolio balance channel.” When a central bank purchases government bonds in the bond market and absorbs the amount of bonds in circulation, the bond price will rise and the yield will decline.
In this case, as the price change is due to the supply and demand factor, the risk premium will decrease and long-term interest rates or longer-term interest rates in general will fall. Second, there is the effect through the risk-neutral forecast of future short-term interest rates.