We present a dynamic asset pricing model based on a heterogenous class of traders. These traders are homogenous in the sense that they are fundamentalists who base their investment decisions on an exogenoulsy given fundamental value. They are heterogenous in the sense that each trader is working with a different frequency of the underlying price data. As a result we have a system of interacting investors who together influence the market price. We derive a system that characterizes out-of-equilibrium dynamics of prices in this market which is structurally equivalent to the Nosé-Hoover thermostat equation in non-equilibrium thermodynamics. We explore the time series properties of these prices and find that they exhibit fat tails of returns distributions, volatility clustering and power laws. (author's abstract) / Series: Working Papers SFB "Adaptive Information Systems and Modelling in Economics and Management Science"

This thesis consists of three essays concerned with endogenous fiscal policy and its interaction with political economy constraints. The first essay presented in Chapter 2 examines the cyclical behavior of endogenous government consumption over the business cycle absent a commitment mechanism in a neoclassical economy with Total Factor Productivity (TFP) shocks and investment shocks. Tax rates that finance public consumption are chosen in a time consistent way in a dynamic game between the government and a representative agent that values public goods in his utility. It is found that government consumption set without commitment behaves procyclical in response to the mentioned shocks. The government-consumption-output ratio is mildly procyclical or countercyclical depending on the selected calibration. Particularly, the elasticity of substitution between private and public goods plays an important role. The second essay showed in Chapter 3 extends the model studied in Chapter 2 adding agent heterogeneity in wealth and labor productivity. The aim of this study is to identify how policy outcomes are affected by inequality of households, particularly the median voter's choice of tax rates that finance public goods. For a standard RBC calibration to the U.S. economy the result is a strong procyclical comovement of public consumption with output, and a relatively weak procyclical comovement of the output share of public consumption with output, that becomes stronger with rising inequality. The politico-economic channel induces causality from output to lagged tax rates, therefore after a Hicks neutral productivity shock the median voter tries to delay the increase in the tax rate, such that the increment will take place just after the accumulation of more capital. In the case of equal agents the response is to decrease the tax rate in the first year after the shock. Additionally, the model predicts that the size of government consumption decreases with inequality. The last essay in Chapter 4 presents a stylized model of external sovereign debt that incorporates corruption in the form of rent-seeking groups by which the choice to cooperate or non-cooperate in providing public goods, in extracting rents and in issuing debt, is endogenized. More than one rent-seeking group originates a "tragedy of the commons" over fiscal resources that make the borrower economy to show collective fiscal impatience. External creditors envision that impatience and require higher interest rates for buying bonds, exacerbating the problem of high debt. The high level of interest rates decreases the wealth of the country and endangers its ability to repay the debt. We show that bailout plans, defined as temporary loans with lower than market level interest rates, are not effective in such economies.

Cette thèse est consacrée à l'étude de la formation des prix sur les marchés financiers, en particulier lorsque ceux-ci se composent d'un grand nombre d'agents. On commence par l'étude empirique d'un marché émergent -- le bitcoin -- de manière à mieux comprendre comment les actions individuelles affectent les prix -- ce que l'on appelle « l'impact de marché ». On développe ensuite un modèle théorique d'impact basé sur le concept d'agent hétérogène, qui parvient à reproduire les observations empiriques d'un impact concave dans un marché non manipulable. Le cadre de l'agent hétérogène nous permet de revisiter les concepts d'offre et de demande dans un cadre dynamique, de mieux comprendre l'impact du mécanisme de marché sur la liquidité, ou encore de poser les bases d'un simulateur de marché réaliste. On montre enfin, à travers l'étude empirique de plusieurs bulles et crashs sur le marché du bitcoin, le rôle crucial de la micro-structure dans la compréhension des phénomènes extrêmes. / This thesis is devoted to the study of price formation on financial markets, in particular when these are composed of a large number of agents. We start by the empirical study of an emergent market -- the bitcoin -- in order to better understand how individual actions impact prices -- a phenomenon known as « market impact ». We then develop a theoretical model based on the concept of heterogeneous agents, that allows to reproduce the empirical observations of a concave impact in a market that remains non-manipulable. The heterogeneous agents framework allows us to revisit the concepts of supply and demand in a dynamic context, to better understand how the choice of a particular market mechanism can impact liquidity, and to lay some grounds for a realistic market simulator. By studying several bubbles and crashes that happened on the bitcoin market, we finally show how relevant microstructure effects can be, in particular for understanding the occurrence of extreme phenomena.