The Core of a Reinsurance Market

In a series of celebrated papers, K. Borch characterized the set of the Paretooptimal risk exchange treaties in a reinsurance market. However, the Paretooptimality and the individual rationality conditions, considered by Borch, do not preclude the possibility that a coalition of companies might be better off by seceding from the whole group. In this paper, we introduce this collective rationality condition and characterize the core of this game without transferable utilities in the important special case of exponential utilities. the mathematical conditions we obtain can be interpreted in terms of insurance premiums, calculated by means of the zero-utility premium calculation principle. We then show that the core is always non-void and conclude by an example. Reinsurance Research - Market Dynamics