  Following the statistical mechanics methodology, firstly introduced in
macroeconomics by Aoki [1996,2002], we provide some insights to the well known
works of Greenwald and Stiglitz [1990, 1993]. Specifically, we reach
analytically a closed form solution of their models overcoming the aggregation
problem. The key idea is to represent the economy as an evolving complex
system, composed by heterogeneous interacting agents, that can partitioned into
a space of macroscopic states. This meso level of aggregation permits to adopt
mean field interaction modeling and master equation techniques.
