We provide theoretical and empirical arguments in favor of a concave shape for the security market line, or a diminishing marginal premium for market risk. In capital market equilibrium with binding portfolio restrictions, different investors generally hold different sets of risky securities....

Modern financial markets offer the real world's best approximation to the idealized price auction market envisioned in economic theory. Nevertheless, as the increasingly exquisite and detailed financial data demonstrate, financial markets often fail to behave as they should if trading were truly...