RESEARCH

Works in Progress

1. Kikcho S.,  M. A.,Marini, R.D. Saulle,  J.-F. Thisse (2026) "Monopolistic Competition under Horizontal and Vertical Differentiation", CEPR Discusssion Paper 12554, 2026;  CESifo WP, 12554, 2026, FEEM Note di Lavoro Series 2026.11. 

Abstract: This paper extends the CES model of monopolistic competition to the case where varieties are both horizontally and vertically differentiated. A distinctive feature of our model is the presence of a network externality, which operates through the number of varieties available at each quality level. Depending on the quality gap, there are corner equilibria in which consumers purchase only high-quality or low-quality varieties, or an interior equilibrium in which consumers are split between the two qualities. Unlike the CES model of monopolistic competition, the equilibrium is never efficient and the market may even select the outcome with the lowest surplus.

2. Iwan Bos,  M. A. Marini, A. Tasnadi (2026) "Endogenous Cournot-Bertrand Duopoly", mimeo.

Abstract:  This note examines a two-stage homogeneous-good duopoly game. In the first stage, firms select price or quantity as their strategic variable and then determine the magnitude of this variable in the second stage. We show the existence of a subgame-perfect Nash equilibrium. In equilibrium, there is one price setter and one quantity setter.

3. Marini, M. A. (2026) "Repeated Coalition Formation Games", mimeo.

Abstract: This paper develops a general theoretical framework for analyzing coalition formation games in a infinitely repeated setting. The coalition formation rule is endogenously determined along a continuous spectrum between two well known canonical rules: the unanimity (or gamma) rule and the aggregative (or delta) rule. We introduce an equilibrium concept whihc is a triple (C, δ, r), where C is a stable coalition structure, δ is the discount factor comon to all agents, and r ∈ [0, 1] parameterizes the coalition formation rule. The parameter r captures the “permissiveness” of the rule—the degree to which coalitions can form without universal consent. We derive general conditions under which a coalition structure can be sustained as a subgame-perfect equilibrium of an infinitely repeated game and characterize the equilibrium correspondence. We apply this framework to cartel formation in Cournot markets, and show that the critical discount factor required to sustain the grand coalition is monotonically increasing in r, with closed-form expressions for the endpoints corresponding to the gamma and delta rules from the literature. Surprisingly, there exist discontinuity thresholds where the maximal sustainable coalition structure jumps.

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