The first chapter questions the conventional intuition that a high concentration of income distribution at the highest level should encourage the emergence of rational asset bubbles. I use an OLG model with heterogeneous financial fictions and agents that differ in terms of saving rates, asset portfolios and talent. I show that a high concentration promotes the emergence of bubbles if and only if these bubbles are illiquid or if all assets offer the same returns. Conversely, when bubbles are liquid and liquid assets pay a liquidity premium, a low concentration promotes the emergence of bubbles. The second paper examines the conditions under which an asset bubble increases GDP in an OLG-New Keynesien model including capital. I show that secular stagnation is a necessary but not sufficient condition. Indeed, bubbles stimulate GDP only if aggregate demand is very deficient. The third paper demonstrates that the New Keynesiens (NK) models make paradoxical predictions when aggregate demand is chronically deficient – a secular boom rather than secular stagnation – and analyses how to adjust these models to make them viable in the current environment. I stress the crucial importance of asset supply and demand elasticities in relation to long-term GDP; I also connect the centuries-old boom with other paradoxical forecasts of the NK model. The first chapter questions the Convention intuition that a high concentration of income at the top of the distribution should promote the emergence of rational asset bubbles. I use an OLG model with financial fictions and heterogeneous agents that differ in terms of saving rate, portfolio choices and skills. I show that a high concentration at the top promots the emergence of asset bubbles if and only if those asset bubbles are illiquid or financial markets are...