Bassel Tarbush

Tutorial Fellow, Merton College and Department of Economics, University of Oxford
Visiting Fellow, Department of Mathematics, London School of Economics and Political Science

News

Merton College is hiring a 4-year post-doc/career development fellowship in economics
Any field of research. There is some teaching (first- and second-year macroeconomics),
…and also a nice housing package, a research allowance, and free breakfast, lunch, and dinner.
More details here. Tell everyone you know and/or apply now! 🔥
Application deadline: 9th of April 2026 at 9am UK time.

ICMS workshop on AI & Economics
March 2026, International Centre for Mathematical Sciences
Videos of keynotes coming here soon.

Symposium on 75 years of Nash equilibrium
July 2025, Maison Française d’Oxford
Videos are now online.

Research

The computational intractability of not worst responding
with Mete Şeref Ahunbay, Paul W Goldberg, Edwin Lock, Panayotis Mertikopoulos, and Bary Pradelski

In progress

abstract   draft

Finding, counting, or determining the existence of Nash equilibria, where players must play optimally given each others’ actions, are known to be computational intractable problems. We ask whether weakening optimality to the requirement that each player merely avoid worst responses yields tractable solution concepts. We show that it does not: any solution concept with this minimal guarantee is as intractable as pure Nash equilibrium.

Game connectivity and adaptive dynamics in many-action games
with Tom Johnston, Michael Savery, and Alex Scott

In progress

abstract   draft

In previous work we showed that, among all n-player k-action generic games that admit a pure Nash equilibrium, the fraction that are connected tends to 1 as n gets sufficiently large relative to k. The present paper considers the large-k regime, which behaves differently: for fixed n ≥ 3, we show that the connected fraction tends to 1 − ζ_n as k gets large, where ζ_n > 0.

Satisficing equilibrium
with Bary Pradelski

In progress

abstract   draft   EC25-abstract

We bring the decision theoretic notion of satisficing, according to which agents play good but not necessarily their best action, to games. We provide static and dynamic foundations for the concept, and consider applications.

Economic dynamics with differential fertility
with Francis Dennig

In progress

abstract   draft

We characterize the outcomes of a canonical theoretical model of the intergenerational transmission of capital that features differential fertility. We establish easy-to-verify conditions on the primitives to guarantee global convergence to degenerate or atomless steady state distributions of capital.

On the existence of pure epsilon-equilibrium
with Bary Pradelski

Revision requested at Journal of Economic Theory

abstract   draft

We show that for any ϵ > 0, as the number of agents gets large, the share of games that admit a pure ϵ-equilibrium converges to 1. The asymptotic share of games that admit a pure Nash equilibrium (i.e. ϵ = 0) is approximately 1 − e⁻¹. Conclusion: very small deviations from perfect rationality suffice to ensure the general existence of stable outcomes.

Game connectivity and adaptive dynamics
with Tom Johnston, Michael Savery, and Alex Scott

Revision requested at Theoretical Economics

abstract   draft

Among generic games that have a pure Nash equilibrium, all but a small fraction are connected, i.e. every non-Nash profile can reach every Nash via directed best-response paths. Implication: there are simple adaptive dynamics that converge almost surely to a pure Nash equilibrium in all but a small fraction of generic games that have one. This limits the scope of known impossibility results about learning pure Nash.

Best-response dynamics, playing sequences, and convergence to equilibrium in random games
with Torsten Heinrich, Yoojin Jang, Luca Mungo, Marco Pangallo, Alex Scott, and Samuel Wiese

International Journal of Game Theory 2023

abstract   article

When played according to a fixed cyclic order, the best-response dynamic converges to a pure Nash equilibrium in a vanishingly small proportion of all large generic games.

Targeted carbon tax reforms
with Maia King and Alex Teytelboym

European Economic Review 2019

abstract   article

We evaluate the general equilibrium impact on aggregate emissions of taxing the emissions of any set of sectors in an intersectoral production network.

Hotelling competition and the gamma distribution

Games and Economic Behavior 2018

abstract   article   code   errata

In any symmetric equilibrium of the pure location game, as the number of firms becomes large, the market share distribution converges to a Gamma(2,2) distribution. The result holds regardless of the distribution of consumers.

Social groups and social network formation
with Alex Teytelboym

Games and Economic Behavior 2017

abstract   article   code   appendix

Dynamic network formation model on a fixed number of nodes and overlapping social groups. Homophily can be non-monotonic over time.

Counterfactuals in “agreeing to disagree”

Mathematical Social Sciences 2016

abstract   article

Interpreting the Sure-Thing Principle as a counterfactual proposition resolves issues with the original “agreeing to disagree” result.