Reserve price of risk-averse search engine in keyword auctions with advertisers' endogenous investment

Motivated by vigorous development of keyword auctions, this paper analyzes the reserve price policies in keyword auction with advertisers' endogenous investment and risk-averse search engine. We explore advertisers' optimal investment and equilibrium bidding strategies and derive the determination functions where utility-maximizing reserve price and efficient reserve price which maximizes the social welfare satisfy respectively. The results show that advertisers' equilibrium bidding is monotonously increasing in bidders' valuations, the number of advertisers, as well as the reserve price. Meanwhile, advertisers' optimal investment is negatively correlated with reserve price and the number of advertisers. By numerical examples, the utility-maximizing reserve price decreases with the risk aversion parameter and the number of advertisers. Search engine's expected utility increases with risk aversion parameter and decreases with the number of advertisers. Moreover, we declare that search engine can use reserve price as a regulatory tool to increase the utility. But there is an upper bound on search engine's utility. It is interesting to find the efficient reserve price equals to zero. Hence there is a trade-off between total efficiency and search engine's utility by search engine that has incentive to withhold reserve price that would benefit social welfare.