Capital market equilibrium with externalities, production and heterogeneous agents

The paper studies general equilibrium in an economy with externalities, production and heterogeneous agents. The model developed builds on Brock [Brock, W.A., 1982. Asset prices in a production economy. In: McCall, J.J. (Ed.), The Economics of Information and Uncertainty. University of Chicago Press, Chicago, pp. 1-43] and Merton [Merton, R.C., 1987. A simple model of capital market equilibrium with incomplete information. Journal of Finance 42, 483-510]; it involves both a stock market and a market for loans, together with negative externalities produced by a subset of firms. Importantly, the technological production structure of the firms is reflected in the properties of the shares traded in the stock market. Agents are heterogeneous in their financial choices, potentially discriminating against the firms producing a negative externality. The model sheds light on the utility costs of the discriminating behavior and on the impact on the price of the stock issued by the firm which is responsible for the externality. The model is used to study the factors which may magnify or reduce the impact of discrimination. A set of discriminated firms may be seriously affected only if the discriminating investors command a large portion of overall wealth and/or they do not represent important diversification instruments. The model can be applied to understanding the effects of socially responsible investment, whereby investors discriminate against companies belonging to some sectors which are perceived as socially dangerous or unethical.