Upcoming Seminars

To see the abstract for any talk, please click anywhere inside the announcement for that talk

Tuesday, 3 February 2026

8PM GMT (12PM Vancouver, 2PM Austin, 3PM Toronto/Montréal, 5PM Rio de Janeiro, 8PM London, 9PM Paris, 11PM Istanbul, 9AM Wednesday in Auckland)

Harvey Lederman (University of Texas, Austin) "Maximal Social Welfare Relations on Infinite Populations Satisfying Permutation Invariance"

Host: Marcus Pivato

Abstract. We study social welfare relations (SWRs) on an infinite population. Our main result is a characterization of the common core shared by prominent utilitarian SWRs over distributions which realize finitely many welfare levels on this population. We characterize them as the largest SWR (with respect to set-inclusion when the weak relation is viewed as a set of pairs) which satisfies Strong Pareto, Permutation Invariance (elsewhere called ``Relative Anonymity'' and ``Isomorphism Invariance''), and a further ``Pointwise Independence'' axiom.

(Joint work with Jeremy Goodman)

Tuesday, 17 February 2026

2PM GMT (9AM College Park, 11AM Rio de Janeiro, 2PM London, 3PM Paris, 5PM Istanbul, 7:30PM New Delhi, 11PM Tokyo/Seoul)

Eric Pacuit (University of Maryland) "Characterizations of voting rules based on majority margins"

Host: Marcus Pivato

Abstract. Abstract: In the context of voting with ranked ballots, an important class of voting rules is the class of margin-based rules (also called pairwise rules). A voting rule is margin-based if whenever two elections generate the same head-to-head margins of victory or loss between candidates, then the voting rule yields the same outcome in both elections. Although this is a mathematically natural invariance property to consider, whether it should be regarded as a normative axiom on voting rules is less clear. In this paper, we address this question for voting rules with any kind of output, whether a set of candidates, a ranking, a probability distribution, etc. We prove that a voting rule is margin-based if and only if it satisfies some axioms with clearer normative content. A key axiom is what we call Preferential Equality, stating that if two voters both rank a candidate x immediately above a candidate y, then either voter switching to rank y immediately above x will have the same effect on the election outcome as if the other voter made the switch, so each voter's preference for y over x is treated equally.