The paper is a very clever and detailed model of "Global Imbalances," "Safe asset shortages" and the zero bound. A country's inability to "produce safe assets" spills, at the zero bound, across to output fluctuations around the world. I disagree with just about everything, and outline an alternative world view.
A quick overview:
Why are interest rates so low? Pierre-Olivier & Co.: countries can't “produce safe stores of value”
This is entirely a financial friction. Real investment opportunities are unchanged. Economies can’t “produce” enough pieces of paper. Me: Productivity is low, so marginal product of capital is low.
Why is growth so low? Pierre-Olivier: The Zero Lower Bound is a "tipping point." Above the ZLB, things are fine. Below ZLB, the extra saving from above drives output gaps. It's all gaps, demand. Me: Productivity is low, interest rates are low, so output and output growth are low.
Data: I Don't see a big change in dynamics at and before the ZLB. If anything, things are more stable now that central banks are stuck at zero. Too slow, but stable. Gaps and unemployment are down. It's not "demand" anymore.
Exchange rates. Pierre-Olivier "indeterminacy when at the ZLB” induces extra volatility. Central banks can try to "coordinate expectations." Me: FTPL gives determinacy, but volatility in exchange rates. There is no big difference at the ZLB.
Safe asset Shortages. Pierre-Olivier: driven by a large mass of infinitely risk averse agents. Risk premia are therefore just as high as in the crisis. Me: Risk premia seem low. And doesn't everyone complain about "reach for yield" and low risk premia?
Observation. These ingredients are plausible about fall 2008. But that's nearly 8 years ago! At some point we have to get past financial crisis theory to not-enough-growth theory.
But, finally, praise. This is a great paper. It clearly articulates a world view, and you can look at the assumptions and mechanisms and decide if you think they make sense. I am in awe that Pierre-Olivier & Co. were able to make a coherent model of these buzzwords.
But great theory is great theory. To a critic, the assumptions are necessary as well as sufficient. I read it as a brilliant negative paper, almost a parody: Here are the extreme assumptions that it takes to justify all the policy blather about "savings gluts" "global imbalances" "safe asset shortages" and so on. To me, it shows just how empty the idea is, that our policy-makers understand any of this stuff at a scientific, empirically-tested level, and should take strong actions to offset the supposed problems these buzzwords allude to.
I hope this taste gets you to read my comments and the paper.