On Finding Equilibrium Stopping Times for Time-Inconsistent Markovian Problems

TL;DR

This paper develops a method to find equilibrium stopping times in time-inconsistent Markovian problems, where traditional optimal stopping concepts do not apply, by adapting consistent planning and variational inequalities.

Contribution

It introduces a new equilibrium concept for time-inconsistent problems, along with an iterative approach and verification theorem for finding equilibrium stopping times.

Findings

Developed an iterative method for equilibrium stopping times.

Proved a verification theorem using variational inequalities.

Applied the theory to a selling strategy problem with utility and habit formation.

Abstract

Standard Markovian optimal stopping problems are consistent in the sense that the first entrance time into the stopping set is optimal for each initial state of the process. Clearly, the usual concept of optimality cannot in a straightforward way be applied to non-standard stopping problems without this time-consistent structure. This paper is devoted to the solution of time-inconsistent stopping problems with the reward depending on the initial state using an adaptation of Strotz's consistent planning. More precisely, we give a precise equilibrium definition --- of the type subgame perfect Nash equilibrium based on pure Markov strategies. In general, such equilibria do not always exist and if they exist they are in general not unique. We, however, develop an iterative approach to finding equilibrium stopping times for a general class of problems and apply this approach to one-sided stopping problems on the real line. We furthermore prove a verification theorem based on a set of variational inequalities which also allows us to find equilibria. In the case of a standard optimal stopping problem, we investigate the connection between the notion of an optimal and an equilibrium stopping time. As an application of the developed theory we study a selling strategy problem under exponential utility and endogenous habit formation.