For decades, textbooks on international economics and finance built a part of their scaffolding on the foundation of a relationship called covered interest parity (CIP). CIP postulates that, in a world of free capital flows, currency-hedged returns on equivalent-risk assets will equalize across countries. For example, the return to investing in a 1-year U.S. Treasury bill will equal the return to purchasing euros, investing the proceeds in a 1-year German Government liability, and purchasing a contract guaranteeing the future euro/dollar exchange rate at which the euros will be converted back to dollars a year later. In practice, the CIP relationship was such a reliable feature of international fixed-income markets that for decades one could think of banks operating a nearly costless CIP machine to perform what many viewed as a riskless arbitrage.

Then, one day, the CIP machine broke down. It first stopped working in the Great Financial Crisis (GFC) of 2007-2009, when counterparty and liquidity risks both skyrocketed, raising the possibility of defaults and losses in executing the trades necessary. That is, CIP was not a riskless arbitrage.

As a wave of recent research highlights, the conventional, pre-crisis model of the CIP machine remains impaired even as the counterparty and liquidity risks that characterized the GFC have receded....