Interest rates are low. Really really low. @ErnestLiuEcon , @AtifRMian , and I just posted a revision of paper, "Low Interest Rates, Market Power, and Productivity Growth". Basic conceptual point: low interest rates can be very bad for firm competition and growth (thread) 1/N 
Suppose decline in interest rates is due to demand-side factors (population aging, rising inequality, global saving glut). How will firms respond to lower interest rates when deciding how much to invest in productivity enhancement? (2/N)
Most economists say: low interest rates are great for investment because they make firms more patient! Not so fast. Low interest rates have been associated with rising market concentration, lower business dynamism, and winner-take-all outcomes. This is not coincidental. (3/N)
By taking strategic interaction between firms seriously, we show a robust theoretical result. Investment by market leaders responds more aggressively to a decline in interest rates than investment by market followers. This is a powerful force leading to more concentration (4/N)
As a result, a decline in interest rates to low and persistent levels in the model is associated with rising market concentration, lower turnover in market leaders, a larger productivity gap between leaders and followers, and eventually lower productivity growth. (5/N)
We see all of these patterns in the data. Low interest rates are not necessarily great for investment in productivity enhancement. In fact, we show theoretically that extremely low interest rates eventually must lower productivity growth (6/N)
Our paper suggests that persistently low interest rates can be bad for the supply side of the economy, and it offers an explanation for why productivity growth has stalled across the world. Link to paper:
scholar.princeton.edu/sites/default/…
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scholar.princeton.edu/sites/default/…
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