No abstract

We develop a government debt management model to study the optimal debt ceiling when the ability of the government to generate primary surpluses to reduce the debt ratio is limited. We succeed in finding a solution for the optimal debt ceiling. We study the conditions under which a country is not able to reduce its debt ratio to reach its optimal debt ceiling, even in the long run. In addition, this model with bounded intervention is consistent with the fact that, in reality, countries that succeed in reducing their debt ratio do not do so immediately, but over some period of time. To the best of our knowledge, this is the first theoretical model on the debt ceiling that accounts for bounded interventions.

Motivated by empirical facts, we develop a theoretical model for optimal currency government debt portfolio and debt payments, which allows both government debt aversion and jumps in the exchange rates. We obtain first a realistic stochastic differential equation for public debt, and then solve explicitly the optimal currency debt problem. We show that higher debt aversion and jumps in the exchange rates lead to a lower proportion of optimal debt in foreign currencies. Furthermore, we show that for a government with extreme debt aversion it is optimal not to issue debt in foreign currencies. To the best of our knowledge, this is the first theoretical model that provides a rigorous explanation of why developing countries have reduced consistently their proportion of foreign debt in their debt portfolios.

We study the optimal control of a government stabilization fund, which is a mechanism to save money during good economic times to be used in bad economic times. The objective of the fund manager is to keep the fund as close as possible to a predetermined target. Accordingly, we consider a running cost associated with the difference between the actual fiscal fund and the fund target. The fund manager exerts control over the fund by making deposits in or withdrawals from the fund. The withdrawals are used to pay public debt or to finance government programs. We obtain, for the first time in the literature, the optimal band for the government stabilization fund. Our results are of interest to practitioners. For instance, we find that the higher the volatility, the larger the size of the optimal band. In particular, each country and state should have its own optimal fund band, in contrast to the “one-size-fits-all” approach that is often used in practice.