Excess Co-movement in Default Risk

Abstract

This paper proposes a new explanation for the observed excess co-movement in default risk across borrowers. In our equilibrium model, a negative idiosyncratic shock to one borrower reduces its creditworthiness but also makes another borrower a relatively larger player in the economy, increasing its systematic risk. This results in higher debt costs for the latter borrower, tilting its decision towards an earlier default, especially when the debt needs to be refinanced more rapidly. We thus identify a novel source of endogenous default risk dependence, which cannot be explained by commonality in fundamentals alone. Given the embedded leverage in equity, this model jointly generates positive excess co-movement in default probability, equity excess returns, and equity return volatility, aligning with new empirical evidence across U.S. industries. These results offer important insights into the interplay between credit and equity markets in a multi-borrower economy.

Keywords: Credit Risk, Structural Models, Asset Prices, Leverage, Volatility, Spillovers

JEL Classification: G12, G13, G32, G33