This dissertation consists of three chapters on banking and monetary economics. In Chapter 1, I study whether monetary policy is less effective in a low interest-rate environment. To answer this question, I examine how the passthrough of monetary policy to banks' deposit rates has changed, during the secular decline in interest rates in the U.S. over the last decades. In the data, the passthrough increased for about one third of banks, and decreased for the rest. Moreover, the deposit-weighted bank-average passthrough increased under a lower interest rate. I explain this observation in a model where banks have market power over loans and face capital constraints. In the model, when interest rates are low, the passthrough falls as policy rates fall, only in markets where loan competition is high. Hence, the overall passthrough depends on the distribution of loan market power. I confirm the model's prediction using branch-level data of U.S. banks. This channel also impacts the transmission of monetary policy to bank lending under low interest rates.

In Chapter 2 (joint with Tsz-Nga Wong), we document a new channel mediating the effects of monetary policy and regulation, the disintermediation channel. When the interest rate on excess reserves (IOER) increases, fewer banks are intermediating in the Fed funds market, and they intermediate less. Thus, the total Fed funds traded decreases. Similarly, disintermediation happens after the balance sheet cost rises, e.g. the introduction of Basel III regulations. The disintermediation channel is significant and supported by empirical evidence on U.S. banks. To explain this channel, we develop a continuous-time search-and-bargaining model of divisible funds and endogenous search intensity that includes the matching model (e.g. Afonso and Lagos, 2015b) and the transaction cost model (e.g. Hamilton, 1996) as special cases. We solve the equilibrium in closed form, derive the dynamic distributions of trades and Fed fund rates, and the stopping times of entry and exit from the Fed fund market. IOER reduces the spread of marginal value of holding reserves, and hence the gain of intermediation. In general, the equilibrium is constrained inefficient, as banks intermediate too much.

In Chapter 3 (joint with Saki Bigio and Eduardo Zilberman), we compare the advantages of lump-sum transfers versus a credit policy in response to the Covid-19 crisis. The Covid-19 crisis has lead to a reduction in the demand and supply of sectors that produce goods that need social interaction to be produced or consumed. We interpret the Covid-19 shock as a shock that reduces utility stemming from "social" goods in a two-sector economy with incomplete markets. For the same path of government debt, transfers are preferable when debt limits are tight, whereas credit policy is preferable when they are slack. A credit policy has the advantage of targeting fiscal resources toward agents that matter most for stabilizing demand. We illustrate this result with a calibrated model. We discuss various shortcomings and possible extensions to the model.