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Social Choice Seminar October 30, 2023 (10:30 AM PDT - 11:30 AM PDT)
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Location: SLMath: Baker Board Room
Speaker(s) Tomer Ezra (Università di Roma "La Sapienza''), Ulrike Schmidt-Kraepelin (Universidad de Chile)
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Tomer Ezra will give an overview talk about truthful mechanisms in subdomains of fair division and voting, followed by a spotlight talk given by Ulrike Schmidt-Kraepelin.

We study the budget aggregation problem in which a set of strategic voters must split a finite divisible resource (such as money or time) among a set of competing projects. Our goal is twofold: We seek truthful mechanisms that provide fairness guarantees to the projects. For the first objective, we focus on the class of moving phantom mechanisms [Freeman et al., 2021], which are -- to this day -- essentially the only known truthful mechanisms in this setting. For project fairness, we consider the mean division as a fair baseline, and bound the maximum difference between the funding received by any project and this baseline. We propose a novel and simple moving phantom mechanism that provides optimal project fairness guarantees. As a corollary of our results, we show that our new mechanism minimizes the l1 distance to the mean (a measure suggested by Caragiannis et al. [2022]) for three projects and gives the first non-trivial bounds on this quantity for more than three projects.

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