Essays in financial and applied microeconomics.

Summary This thesis is composed of three independent papers that have in common the analysis of the behavior of investors and firms under imperfect competition. We first consider a Kyle (1985) model of the financial market where investors can produce either a (fundamental) signal on the value of a risky asset or a (non-fundamental) signal on the random demand of noise traders. We show that reducing the cost of the non-fundamental signal worsens the informational efficiency of the stock price and, under certain conditions, the welfare of noise traders. We then extend the model to the case where non-fundamentalists submit limit orders. Their activity is then similar to "front running". We then consider a Kyle (1985) style market where uninformed agents trade for a risk-sharing motive with investors spread over a network, who share their signals with their contacts, which formalizes a better diffusion of information. We then evaluate the effect of this hypothesis on two criteria: speculative profit and the utility expectation of uninformed agents, which measures the efficiency of risk sharing in the market. We show that the addition of the network can simultaneously improve these two criteria as well as the informational efficiency of the price. An original result that cannot be obtained without the addition of the network. Finally, we characterize the gradual cooperation between two competing firms of different sizes that are unable to contract and whose contributions are irreversible. We show that the asymmetry between the two firms strongly slows down the collaboration process, which underlines the importance of contractual arrangements in certain situations. We also show that increased competition between the two firms can harm social welfare by reducing their ability to collaborate.