Modèles d'équilibre général dynamique stochastique

Un modèle d'équilibre général dynamique stochastique (en anglais, Dynamic Stochastic General Equilibrium, DSGE) est un modèle économique qui se base sur la théorie de l'équilibre général afin de permettre d'évaluer l'impact macroéconomique d'une politique monétaire ou budgétaire. Le modèle DSGE a été créé par l'école de la nouvelle économie keynésienne sur la base des travaux des modèles de cycles réels (modèles RBC) de Finn E. Kydland et Edward C. Prescott. Les modèles DSGE jouent un rôle majeur dans l'évaluation de l'impact macroéconomique des politiques économiques actuelles. Ces modèles sont utilisés, notamment, par les banques centrales et les institutions internationales comme le Fonds monétaire international. Ces modèles reposent sur deux principes. Tout d'abord, sur une modélisation des agents économiques au niveau microéconomiques, avec une prise en compte des ménages, des entreprises et de l'État ; ensuite, sur des données passées qui permettent de calibrer le modèle et l'affiner. Les agents économiques sont considérés comme maximisant leurs utilités (pour les entreprises, leurs profits). L'objectif est de modéliser les variables macroéconomiques telles que la croissance économique, l'inflation, le chômage, etc. Le modèle est dit stochastique car il consiste pour le chercheur à introduire des processus stochastiques exogènes (dits ) qui modélisent un changement dans le système économique. Dans ces modèles, l'état de l'économie évolue par palier passant de l'instant t à l'instant t+1, les maximisations s'effectuent donc sur l'espérance de la somme des utilités ou des profits futurs tout en tenant compte des contraintes (prix, monnaie,...). Les modèles DSGE sont issus d'un article séminal écrit par Finn E. Kydland et Edward C. Prescott, considéré comme le point de départ de cette branche des sciences économiques. Aujourd'hui, deux grandes écoles de pensée économiques utilisent ces modèles, avec des paramètres différents : la Nouvelle économie classique, avec des prix libres, et la Nouvelle économie keynésienne, avec des prix imposés par des entreprises monopolistiques.

Polynomial models in finance

Damien Edouard Ackerer

This thesis presents new flexible dynamic stochastic models for the evolution of market prices and new methods for the valuation of derivatives. These models and methods build on the recently characterized class of polynomial jump-diffusion processes for which the conditional moments are analytic. The first half of this thesis is concerned with modelling the fluctuations in the volatility of stock prices, and with the valuation of options on the stock. A new stochastic volatility model for which the squared volatility follows a Jacobi process is presented in the first chapter. The stock price volatility is allowed to continuously fluctuate between a lower and an upper bound, and option prices have closed-form series representations when their payoff functions depend on the stock price at finitely many dates. Truncating these series at some finite order entails accurate option price approximations. This method builds on the series expansion of the ratio between the log price density and an auxiliary density, with respect to an orthonormal basis of polynomials in a weighted Lebesgue space. When the payoff functions can be similarly expanded, the method is particularly efficient computationally. In the second chapter, more flexible choices of weighted spaces are studied in order to obtain new series representations for option prices with faster convergence rates. The option price approximation method can then be applied to various stochastic volatility models. The second half of this thesis is concerned with modelling the default times of firms, and with the pricing of credit risk securities. A new class of credit risk models in which the firm default probability is linear in the factors is presented in the third chapter. The prices of defaultable bonds and credit default swaps have explicit linear-rational expressions in the factors. A polynomial model with compact support and bounded default intensities is developed. This property is exploited to approximate credit derivatives prices by interpolating their payoff functions with polynomials. In the fourth chapter, the joint term structure of default probabilities is flexibly modelled using factor copulas. A generic static framework is developed in which the prices of high dimensional and complex credit securities can be efficiently and exactly computed. Dynamic credit risk models with significant default dependence can in turn be constructed by combining polynomial factor copulas and linear credit risk models.

EPFL2017

Financial Frictions within the Macroeconomy

Victoria Nuguer

Financial factors are central to the recent economic crisis. Most macroeconomic models treat banks and financial intermediation as a veil. These models are unable to account for the recent financial crisis and they cannot be used for policy evaluation. Financial frictions include default on mortgages, disruptions in financial intermediation, and informational asymmetries, among others. In my dissertation, I propose to analyze the effects of policy in economic models characterized by financial frictions. The thesis is composed of three chapters. The first chapter is joint work with Luisa Lambertini and Pinar Uysal. We explicitly model the housing sector, mortgages, and endogenous default as well as nominal and real rigidities in a dynamic stochastic general equilibrium (DSGE) setting. We use U.S. data for the period 1981-2006 to estimate our model using Bayesian techniques. Our starting point is to have an empirically plausible model with endogenous default in mortgages that can explain the main features of the macroeconomic time series. We analyze how an increase in the mortgage default rate can spread to the rest of the economy and result in a recession. Next we examine different policy options that might mitigate the effects of an increase in the mortgage default rate. In the second chapter I develop a two-country DSGE model with global banks (financial intermediaries in one country lend to banks in the other country). Banks are financially constrained on how much they can borrow from households. The main goal is to obtain a framework that captures the international transmission of a financial crisis through the balance sheet of the global banks as well as to explain the insurance mechanism of the international asset market. A negative shock to the value of the capital in one country generates a global financial crisis through the international interbank market. The third chapter uses the above model to analyze the policy challenges that global banks face. In this chapter, I look at how different unconventional unilateral credit policies help to mitigate the effects of a financial disruption. First, the policies are carried out only by the policy maker of the country directly hit by the shock. Consumers of the country where the intervention and the shock take place are better off with policy than without it; consumers from the other country are worse off. Second, I allow for both policy makers to intervene. Both countries intervening help to reduce the negative effects of the country that is not directly hit by the shock but the intervention is not a Pareto improvement.

EPFL2014