Agency mortgage‐backed securities (MBSs) with diverse characteristics are traded in parallel through individualized specified pool (SP) contracts and standardized to‐be‐announced (TBA) contracts with delivery flexibility. This parallel trading environment generates distinctive effects on MBS pricing and trading: (i) Although cheapest‐to‐deliver (CTD) issues are present in TBA trading and absent from SP trading by design, MBS heterogeneity associated with CTD discounts affects SP yields positively, with the effect stronger for lower‐value SPs; (ii) high selling pressure amplifies the effects of MBS heterogeneity on SP yields; and (iii) greater MBS heterogeneity dampens SP and TBA trading activities but increases their ratio.

This paper studies asset pricing under expectations‐based reference‐dependent preferences in a general equilibrium framework. We show that reference‐dependent preferences can generate self‐fulfilling risk panics, producing sentiment‐driven asset price fluctuations through a feedback loop between current prices and perceived future downside risk—dynamics impossible under standard expected utility. The model helps explain empirical puzzles including (i) excess volatility, (ii) asymmetric volatility, (iii) asymmetric sentiment over the business cycle, (iv) excess asset price comovement, and (v) weak correlations between stock returns and economic fundamentals, alongside a sizable equity premium. Additional empirical evidence based on closed‐end fund discounts and quantitative analysis support the theory.