Jump Bidding and Overconcentration in DecentralizedSimultaneous Ascending Auctions

A model of English auction that allows jump bidding is proposed. When twoobjects are sold separately via such English auctions, I construct an equilibrium suchthat bidders signal via jump bids, thereby forming rational expectations of the priceswithout relying on any central mediator. This equilibrium eliminates the exposureproblem for a bidder whose valuation function is superadditive. Consequently, theauction game overly concentrates the goods to a multi-item bidder and never overlydiffuses them to single-item bidders.[...]