A Current Benefit-Cost Ratio of 0.55 Is Sufficient to Make Increased Federal Purchases a Good Deal Today...

Proofing DeLong and Summers, "Fiscal Policy in a Depressed Economy":

Note that that required current-dollar 0.55 benefit-cost ratio includes as benefits:

• direct utility provided to current citizens,
• the present value of future GDP boosts from government capital,
• current aggregate-demand externalities, and
• the present value of future GDP boosts from reduced hysteresis effects on potential output.

At these interest rates, we surely are in the world of Abba Lerner's "functional finance"...