Negli ultimi dieci anni siamo stati testimoni di una delle più grandi crisi che il mondo ha visto. Il lavoro dei macroeconomisti è diventato più attivo, nell'urgenza di trovare la via d'uscita, molti degli strumenti applicati per la professione di economista sono stati rispolverati ed aggiornati per le nuove esigenze della crisi economica. Tra gli strumenti per la ricerca economica c'è lo modello dinamico stocastico di equilibrio generale (DSGE). Questa tesi è composta da quattro capitoli che coinvolgono l'intermediazione e/o politiche condotte dai governi o banche centrali finanziarie. I primi tre capitoli partono sul modello DSGE mentre l' ultimo su un modello macroeconomico principale-agente. Il primo (scritto come una rassegna delle principali indagini in DSGE) trata dei cicli di credito, di acceleratori finanziari, del mercato immobiliare, del settore bancario, dell'assunzione dei rischi e delle politiche monetarie. Il secondo analizza l'impatto delle variazioni tra il rapporto di leva e le riserve necessarie all'interno, che al giorno d'oggi regolano alcune delle politiche popolari. Il terzo capitolo incorpora un mercato dei prestiti interbancari per l'analisi degli shock di rischio generato nel settore bancario e come si sviluppa l'economia. Il quarto invece è un'indagine che si scosta dal modello macroeconomico principale-agente; comprende un governo attivo con le tasse e sussidi di disoccupazione. / During the last decade we were witness of one of the biggest crises that the world has seen. The job of the macroeconomists became more active, in the urgency for finding the way out; many of the tools applied for the economist profession were dusted off and updated for the new needs of the economic crisis. Among the tools for economic research there is the Dynamic Stochastic General Equilibrium Model (DSGE). This dissertation consists of four chapters involved in financial intermediation and/or policies conducted by the governments or central banks. The first three chapters depart from the DSGE model while the last is a macroeconomic agent based model. The first, written as a review of the main investigations in the DSGE, covers several fields as credit cycles, financial accelerator, housing market, banking sector, risk taking and monetary policies. The second chapter analyses the impacts of changes in the leverage ratio and the required reserves within, some of the popular regulation policies nowadays. The third chapter incorporates an interbank lending market for the analysis of risk shocks generated in the banking sector and how it is spread to the economy. The fourth chapter is an investigation that departs from the macroeconomic agent based model; it incorporates an active government with taxes and unemployment subsidies.

This thesis considers how fiscal and monetary policy should be conducted in resourcerich economies. It consists of three papers addressing: whether governments should spend, save or invest volatile oil income; the assets they should save in; and how monetary policy should respond. The first, “Eight principles for managing resource wealth”, shows that capital-scarce countries should save relatively less against oil price volatility, and invest more in domestic capital. They also should prepare for volatility in advance, and treat savings as a source of income rather than a temporary buffer. To show this the paper develops a framework that nests a variety of existing results, which are presented in eight principles. The second, “The Elephant in the Ground: Oil extraction and asset allocation in sovereign wealth funds”, shows that governments should use sovereign wealth funds to offset oil price risk, extract oil faster if its price is pro-cyclical, and use precautionary savings to manage any residual volatility. To do this it combines three strands of literature for the first time: on continuous-time portfolio theory, oil extraction and precautionary savings. The third, “Optimal monetary responses to oil discoveries”, addresses the anticipation effects around an oil discovery. It shows that the terms of trade will need to appreciate twice: once when oil is discovered and consumers anticipate future revenues; and again when the government begins spending the revenues. Oil wealth will give the monetary authority an incentive to appreciate the terms of trade, in addition to stabilising domestic inflation and the output gap. Optimal policy is well-approximated by a standard monetary rule that also responds to expected changes in the natural level of output.

Thesis (doctoral) - Freie Universität, Berlin, 2005. / Includes bibliographical references (p. 189-203).

Cette thèse traite des interactions entre les sphères financière et réelle de l'économie. Elle se compose de quatre chapitres. Dans les deux premiers chapitres, nous étudions l'existence et les fluctuations d'une bulle spéculative rationnelle, comme source de la volatilité des prix d'actifs, en prenant en compte les imperfections financières dans la modélisation des choix des ménages. L'existence d'un choix de portefeuille et de frictions financières favorisent l'émergence des fluctuations d'une bulle et des cycles économiques endogènes. Dans un tel contexte, nous analysons le rôle stabilisateur des politiques fiscales et/ou monétaires. Dans le chapitre 1, nous montrons qu'une politique monétaire répondant aux prix des actifs permet de stabiliser l'économie dans son ensemble. Dans le chapitre 2, nous comparons les vertus stabilisatrices d'un impôt progressif sur le revenu de capital à celles d'une politique monétaire régie par une règle de Taylor. Nous montrons qu'un impôt progressif sur le capital permet de stabiliser l'économie en réduisant la probabilité d'apparition des fluctuations endogènes, alors qu'une règle de Taylor a des vertus stabilisatrices mitigées. Nous étudions, dans le chapitre 3, l'existence de bulles rationnelles dans une économie ouverte à deux pays et la transmission internationale de leur éclatement. L'éclatement de la bulle dans un pays se transmet nécessairement à l'autre pays. L'effet de l'éclatement peut être positif ou négatif sur l'autre pays. Dans le chapitre 4, nous analysons le rôle de l'hétérogénéité sur la dynamique des prix d'actifs et les inégalités lorsque les agents ont des préférences pour la richesse. / This thesis deals with the interplay between the financial and real sectors of the economy. This thesis consists of four chapters. In the first two chapters, we study the existence and endogenous fluctuations of rational speculative bubbles, as a source of volatility in asset prices, taking into account the financial imperfections at the household level. We argue that the existence of a portfolio choice and financial frictions promote the emergence of bubble fluctuations and endogenous business cycles. In this context, we analyze the stabilizing role of fiscal and/or monetary policies. In Chapter 1, we show that a monetary policy responding to asset prices can stabilize the economy as a whole. In Chapter 2, we compare the stabilizing virtues of a progressive taxation on capital income with those of a monetary policy managed by a Taylor rule. We show that a progressive taxation on capital may rule out endogenous fluctuations, whereas a monetary policy under a Taylor rule has a mitigated stabilizing role. In Chapter 3, we study, the existence of rational bubbles in a two-country economy, and the international transmission of their bursting. A bubble bursting in a country necessarily transmits to the othercountry. The effect of a bubble crash in one country onthe bubble issued by the other country can be positive or negative. In Chapter 4, we analyze the role of heterogeneity on the dynamics of asset prices and inequalities when economic agents have preferences for wealth. Heterogeneity in preferences, but also in income, can heighten social inequalities and increase the asset price in the long run, but also promote asset price volatility in the short run.