Conventional business cycle analysis interprets economic

fluctuations as high frequency variations around an exogenous trend. In

contrast to this approach, we include two sources of growth (ideas and

knowledge) to determine the endogenous trend of an economy, and examine its

quantitative potential in a standard medium scale New Keynesian

model. We estimate this model on the US data between 1950q1-2018q4 with an

occasionnally binding constraint on the nominal rate. We find that the

endogenous trend has been sharply declining since 1970, thus corroborating the

secular stagnation theory. This dynamic is captured by a slowdown in the

accumulation technology reflecting the low productivity of the R\&D sector.

While the contribution of human capital has been remarkably stable, the

financial crisis deteriorated its contribution over the last decade.