Rational bubbles occur when people believe that prices will increase into the infinite future, which makes that they invest in more assets and prices really increase. But equilibrium models have difficulties replicating such phenomena because this increased wealth also induces, at some point, people to consume more, and then the budget constraint bites and halts the bubble. So how could one still get a rational bubble? By relaxing the budget constraint.
This is what Christopher Reicher does in a way that is reminiscent of the US before the crisis: through the provision of unlimited credit, which is possible if real estate is used as collateral. This sounds rather intuitive, as long as lenders are willing to go along. What is more interesting is that the model shows that there are monetary and fiscal policies that can prevent bubbles from happening. One is to apply the fiscal theory of the price level to credit markets, that is, to make sure the price level instantaneously responds to land prices to deflate the debt. If this is difficult to implement, and it would, another way to deflate a bubble is the make sure the returns of assets are lower by increasing interest rates of bonds, which makes them more interesting than real estate. Of course, one could also tax away the bubble. And one has first to recognize that there is a bubble.