Dynamic bank capital regulation in the presence of shadow banks

Regulated banks expand relative to shadow banks in recessions and when credit spreads are high, while regulated banks shrink relative to shadow banks in expansions and when credit spreads are low. Motivated by these facts, I build a quantitative general equilibrium model with endogenous risk taking to study how competitive interactions between regulated banks and shadow banks affect optimal dynamic capital requirements. Limited liability and deposit insurance can lead regulated banks to provide socially inefficient risky loans when the returns on safer loans decline. Competition for scarcer funding can further lower the net returns on safe loans, making it more attractive for regulated banks to exploit the shield of limited liability with risky loans. Higher capital requirements can reduce inefficient risk at the cost of lower liquidity provision and some migration of credit from regulated banks to shadow banks. Accounting for the interactions of regulated and shadow banks can change the magnitude and direction of the optimal response of capital requirements to shocks that drive the business cycle. Moreover, Basel-III style rules that differentiate between the type of bank loans are much better at mimicking the Ramsey optimal capital requirements than standard rules that aggregate loans. The performance of such dynamic rules can be further improved once they are combined with a small static capital buffer.