Many allege that the long run of low interest rates post global financial crisis lowered productivity growth via zombie firms. These low productivity firms survived more than they should have done and hence productivity growth stalled.
An alternative view is that low productivity growth, for other reasons, lowered r* and hence interest rates.
A paper "Aggregate productivity decompositions using structural business surveys: Evidence from the UK by Russell Black, Rebecca Riley and Garry Young", available here sheds a bit of light on this for the UK.
It uses UK company data to decompose productivity growth into that
a. within surviving companies
b. reallocation of market share between surviving companies
c. the net effect of exit and entry.
One might think that the zombie firms view would say that the net entry/exit effect would be less as fewer low productivity firms exit.
Their chart shows this isn't the case.
2. instead, the fall in productivity growth is due more or less equally to falling within firm growth and falling between firm reallocation. The latter might be a zombie phenominon, but it isn't clearly so.