Endogenous formation of alliances in conflicts

This paper studies the endogenous formation of alliance in conflicts offering a survey of the recent literature and providing new results. We analyze the effect of group sizes on conflict, study endogenous alliance formation in a general model of conflict with linear technology and discuss recent developments of the theory of alliance formation, involving the determination of sharing rules inside the alliance and dynamic alliance formation in nested conflicts.alliance formation, conflicts, rent-seeking contest, collective action, the paradox of group size, sharing rules, nested conflicts

Correlated equilibria, incomplete information and coalitional deviations

This paper proposes new concepts of strong and coalition-proof correlated equilibria where agents form coalitions at the interim stage and share information about their recommendations in a credible way. When players deviate at the interim stage, coalition-proof correlated equilibria may fail to exist for two-player games. However, coalition-proof correlated equilibria always exist in dominance-solvable games and in games with positive externalities and binary actions

Communication networks with endogenous link strength

This paper analyzes the formation of networks when players choose how much to invest in each relationship. We suppose that players have a fixed endowment that they can allocate across links, and in the baseline model, suppose that link strength is an additively separable and convex function of individual investments, and that agents use the path which maximizes the product of link strengths. We show that both the stable and efficient network architectures are stars. However, the investments of the hub may differ in stable and efficient networks. Under alternative assumptions on the investment technology and the reliability measure, other network architectures can emerge as efficient and stable

Access Pricing and Entry in the Postal Sector

Postal markets have been open to competition for a long time. But, with a few exceptions, the competitors of the incumbent postal operator are active on the upstream segments of the market -preparation, collection, outward sorting and transport of mail products. With the further steps planned in the liberalization process, there are new opportunities to extend competition to the downstream segments of the market -the delivery of mails. In the future, two business models will be possible for the new postal operators: (1) access: where the firm performs the upstream operations and uses the incumbent’s delivery network and (2) bypass where the competing firm controls the entire supply chain and delivers mails with its own delivery network. These two options have different impacts on welfare and the profit of the incumbent operator. The choice between access and bypass depends on the entrant's delivery cost relative to the cost of buying access to the incumbent operator (the access price). In this paper, we derive optimal -welfare maximizing- stamp and access prices for the incumbent operator when these prices have an impact on the delivery method chosen by the entrant. We show how prices should be re-balanced when the entry method is considered as endogenous i.e. affected by the incumbent's prices.

Agenda Control in Coalition Formation

Theoretical models of government formation in political science usually assume that the head of state is non-strategic. In this paper, we analyze the power of an agenda setter who chooses the order in which players are recognized to form coalitions in simple games. We characterize those sets of players which can be imposed in the equilibrium coalition and show that the only decisive structures where the agenda setter can impose the presence of any minimal winning coalition are apex games, where a large player forms a winning coalition with any of the small players.Agenda Control; Cabinet Formation; Simple Games

Pricing in networks

This paper studies optimal pricing in networks in the presence of local consumption or price externalities. It analyzes the relation between prices and nodal centrality measures. Using an asymptotic approach, it shows that the ranking of optimal prices and strategies can be reduced to the lexicographic ranking of a specific vector of nodal characteristics. In particular, this result shows that with positive consumption externalities, prices are higher at nodes with higher degree, and with relative price externalities, prices are higher at nodes which have more neighbors of smaller degree.Social Networks, Network Externalities, Oligopolies

Markovian assignment rules

We analyze dynamic assignment problems where agents successively receive different objects (positions, offices, etc.). A finite set of n vertically differentiated indivisible objects are assigned to n agents who live n periods. At each period, a new agent enters society, and the oldest agent retires, leaving his object to be reassigned. We define independent assignment rules (where the assignment of an object to an agent is independent of the way other objects are allocated to other agents), efficient assignment rules (where there does not exist another assignment rule with larger expected surplus), and fair assignment rules (where agents experiencing the same circumstances have identical histories in the long run). When agents are homogenous, we characterize efficient, independent and fair rules as generalizations of the seniority rule. When agents draw their types at random, we prove that independence and efficiency are incompatible, and that efficient and fair rules only exist when there are two types of agents. We characterize two simple rules (type-rank and type-seniority) which satisfy both efficiency and fairness criteria in dichotomous settings.dynamic assignment, finite Markov chains, seniority, promotion rules

Communication Networks with Endogenous Link Strength

This paper analyzes the formation of communication networks when players choose endogenously their investment on communication links. We consider two alternative de?nitions of network reliability ; product reliability, where the decay of information depends on the product of the strength of communication links, and min reliability where the speed of connection is a¤ected by the weakest communication link. When investments are separable, the architecture of the efficient network depends crucially on the shape of the transformation function linking investments to the quality of communication links. With increasing marginal returns to investment, the efficient network is a star ; with decreasing marginal returns, the con?ict between maximization of direct and indirect bene?ts prevents a complete characterization of efficient networks. However, with min reliability, the efficient network must be a tree. Furthermore, in the particular case of linear transformation functions, in an e¢ cient network, all links must have equal strength. When investments are perfect complements, the results change drastically : under product reliability, the efficient network must contain a cycle, and is in fact a circle for small societies. With min reliability, the e¢ cient network is either a circle or a line. As in classical models of network formation, e fficient networks may not be supported by private invesment decisions. We provide examples to show that the star may not be stable when the transformation functions is strictly convex. We also note that with perfect substitutes and perfect complements (when the e¢ cient network displays a very symmetric structure), the e¢ cient network can indeed be supported by private investments when the society is large.communication networks ; network reliability

The Formation of Networks with Side Payments

We examine the formation of networks among a set of players whose payoffs depend on the structure of the network. We focus on games where players may promise or demand transfer payments when forming links. If players may only make such transfers on the links they are directly involved with, then there are many settings where inefficient networks are the only equilibrium outcomes, and we fully characterize the supportable networks. If externalities are nonpositive and a convexity condition is satisfied, then efficient networks are supportable as equilibria with such direct transfers. If players can also make positive transfers to pay for links they are not involved with, then a convexity condition alone is sufficient for an efficient network to be supportable as an equilibrium. In cases where transfers can be made contingent on the network, then any efficient network is supportable as an equilibrium. We also consider a refinement of equilibrium that allows pairs of players to coordinate their promises and demands on a link. If players can make payments to prevent the formation of a link as well as to form it, then all efficient networks are supportable via the pairwise equilibrium refinementnetwork formation, side-payments

Market Sharing Agreements and Collusive Networks

This paper analyzes the formation of market sharing agreements among firms in oligopolistic markets and procurement auctions. The set of market sharing agreements defines a collusive network, and the paper provides a complete characterization of stable and efficient collusive networks when firms and markets are symmetric. Efficient networks are regular networks, where firms have the same number of market sharing agreements. Stable networks are formed of complete alliances, of different sizes, larger than a minimal threshold. Typically, stable networks display fewer market sharing agreements than the optimal network for the industry and more market sharing agreements than the socially optimal network. When firms or markets are asymmetric, incomplete alliances can form in stable networks, and stable networks may be underconnected with respect to the social optimum.Market sharing, Collusion, Economic networks, Oligopoly, Auctions