Stable International Environmental Agreements: An Analytical Approach

In this paper we examine the formation of International Environmental Agreements (IEAs). We provide an analytical treatment of the main model used in the literature and offer a formal solution of it (which has not been available so far), while we clarify some misconceptions that exist in the literature. We find that the unique stable IEA consist of either two, three or four signatories if the number of countries is greater than or equal to 5. Furthermore, we show that the welfare of the signatories of a stable IEA is very close to its lowest level vs the welfare of signatories of other non-stable IEAs. While in our model countries' choice variable is emissions, we extend our results to the case where the choice variable is abatement efforts.International Environmental Agreements, Coalition Formation

Stable International Environmental Agreements: An Analytical Approach

In this paper we examine the formation of International Environmental Agreements (IEAs). We show that the welfare of the signatories does not increase monotonically with respect to the number of signatories. We provide an analytical solution of the leadership model. In particular, we find that the unique stable IEA consist of either two, three or four signatories if the number of countries is greater than 4. Furthermore, we show that the welfare of the signatories is almost at its lowest level when the IEA is stable. While in our model countries’ choice variable is emissions, we extend our results to the case where the choice variable is abatement efforts.

Merger Performance under Uncertain Efficiency Gains

In view of the uncertainty over the ability of merging firms to achieve efficiency gains, we model the post-merger situation as a Cournot oligopoly wherein the outsiders face uncertainty about the merged entity’s final cost. At the Bayesian equilibrium, a bilateral merger is profitable provided that non-merged firms sufficiently believe that the merger will generate large enough efficiency gains, even if ex post none actually materialize. The effects of the merger on market performance are shown to follow similar threshold rules. The findings are broadly consistent with stylized facts, and provide a rationalization for an efficiency consideration in merger policy.Horizontal merger, Bayesian Cournot equilibrium, Efficiency gains, Market performance

Sharing the surplus in games with externalities within and across issues

We consider environments in which agents can cooperate on multiple issues and externalities are present both within and across issues. We propose a way to extend (Shapley) values that have been put forward to deal with externalities within issues to games where there are externalities within and across issues. We characterize our proposal through axioms that extend the Shapley axioms to our more general environment.externalities, cooperative game theory, Shapley value, linked issues.

Random paths to stability in the roommate problem

This paper studies whether a sequence of myopic blockings leads to a stable matching in the roommate problem. We prove that if a stable matching exists and preferences are strict, then for any unstable matching, there exists a finite sequence of successive myopic blockings leading to a stable matching. This implies that, starting from any unstable matching, the process of allowing a randomly chosen blocking pair to form converges to a stable matching with probability one. This result generalizes those of Roth and Vande Vate (1990) and Chung (2000) under strict preferences

Sharing the surplus in games with externalities within and across issues

Financial support from ECO2009-7616, ECO2012-31962, 2014SGR-142, the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2011-0075), ICREA AcademiaWe consider issue-externality games in which agents can cooperate on multiple issues and externalities are present both within and across issues, that is, the amount a coalition receives in one issue depends on how the players are organized on all the issues. Examples of such games are several Örms competing in multiple markets, and countries negotiating both a trade agreement (through, e.g., WTO) and an environmental agreement (e.g., Kyoto Protocol). We propose a way to extend (Shapley) values for partition function games to issue-externality games. We characterize our proposal through axioms that extend the Shapley axioms to our more general environment. The solution concept that we propose can be applied to many interesting games, including intertemporal situations where players meet sequentially

Matching Dynamics with Constraints

We study uncoordinated matching markets with additional local constraints that capture, e.g., restricted information, visibility, or externalities in markets. Each agent is a node in a fixed matching network and strives to be matched to another agent. Each agent has a complete preference list over all other agents it can be matched with. However, depending on the constraints and the current state of the game, not all possible partners are available for matching at all times. For correlated preferences, we propose and study a general class of hedonic coalition formation games that we call coalition formation games with constraints. This class includes and extends many recently studied variants of stable matching, such as locally stable matching, socially stable matching, or friendship matching. Perhaps surprisingly, we show that all these variants are encompassed in a class of "consistent" instances that always allow a polynomial improvement sequence to a stable state. In addition, we show that for consistent instances there always exists a polynomial sequence to every reachable state. Our characterization is tight in the sense that we provide exponential lower bounds when each of the requirements for consistency is violated. We also analyze matching with uncorrelated preferences, where we obtain a larger variety of results. While socially stable matching always allows a polynomial sequence to a stable state, for other classes different additional assumptions are sufficient to guarantee the same results. For the problem of reaching a given stable state, we show NP-hardness in almost all considered classes of matching games.Comment: Conference Version in WINE 201

Sharing the surplus in games with externalities within and across issues

We consider environments in which agents can cooperate on multiple issues and externalities are present both within and across issues. We propose a way to extend (Shapley) values that have been put forward to deal with externalities within issues to games where there are externalities within and across issues. We characterize our proposal through axioms that extend the Shapley axioms to our more general environment

On the Core of Dynamic Cooperative Games

We consider dynamic cooperative games, where the worth of coalitions varies over time according to the history of allocations. When defining the core of a dynamic game, we allow the possibility for coalitions to deviate at any time and thereby to give rise to a new environment. A coalition that considers a deviation needs to take the consequences into account because from the deviation point on, the game is no longer played with the original set of players. The deviating coalition becomes the new grand coalition which, in turn, induces a new dynamic game. The stage games of the new dynamical game depend on all previous allocation including those that have materialized from the deviating time on. We define three types of core solutions: fair core, stable core and credible core. We characterize the first two in case where the instantaneous game depends on the last allocation (rather than on the whole history of allocations) and the third in the general case. The analysis and the results resembles to a great extent the theory of non-cooperative dynamic games.Comment: 25 page