Game Theory

Optimal position-building strategies in competition ArXiv ID: 2409.03586 “View on arXiv” Authors: Unknown Abstract This paper develops a mathematical framework for building a position in a stock over a fixed period of time while in competition with one or more other traders doing the same thing. We develop a game-theoretic framework that takes place in the space of trading strategies where action sets are trading strategies and traders try to devise best-response strategies to their adversaries. In this setup trading is guided by a desire to minimize the total cost of trading arising from a mixture of temporary and permanent market impact caused by the aggregate level of trading including the trader and the competition. We describe a notion of equilibrium strategies, show that they exist and provide closed-form solutions. ...

MEV Capture and Decentralization in Execution Tickets ArXiv ID: 2408.11255 “View on arXiv” Authors: Unknown Abstract We provide an economic model of Execution Tickets and use it to study the ability of the Ethereum protocol to capture MEV from block construction. We demonstrate that Execution Tickets extract all MEV when all buyers are homogeneous, risk neutral and face no capital costs. We also show that MEV capture decreases with risk aversion and capital costs. Moreover, when buyers are heterogeneous, MEV capture can be especially low and a single dominant buyer can extract much of the MEV. This adverse effect can be partially mitigated by the presence of a Proposer Builder Separation (PBS) mechanism, which gives ET buyers access to a market of specialized builders, but in practice centralization vectors still persist. With PBS, ETs are concentrated among those with the highest ex-ante MEV extraction ability and lowest cost of capital. We show how it is possible that large investors that are not builders but have substantial advantage in capital cost can come to dominate the ET market. ...

Reinforcement Learning in High-frequency Market Making ArXiv ID: 2407.21025 “View on arXiv” Authors: Unknown Abstract This paper establishes a new and comprehensive theoretical analysis for the application of reinforcement learning (RL) in high-frequency market making. We bridge the modern RL theory and the continuous-time statistical models in high-frequency financial economics. Different with most existing literature on methodological research about developing various RL methods for market making problem, our work is a pilot to provide the theoretical analysis. We target the effects of sampling frequency, and find an interesting tradeoff between error and complexity of RL algorithm when tweaking the values of the time increment $Δ$ $-$ as $Δ$ becomes smaller, the error will be smaller but the complexity will be larger. We also study the two-player case under the general-sum game framework and establish the convergence of Nash equilibrium to the continuous-time game equilibrium as $Δ\rightarrow0$. The Nash Q-learning algorithm, which is an online multi-agent RL method, is applied to solve the equilibrium. Our theories are not only useful for practitioners to choose the sampling frequency, but also very general and applicable to other high-frequency financial decision making problems, e.g., optimal executions, as long as the time-discretization of a continuous-time markov decision process is adopted. Monte Carlo simulation evidence support all of our theories. ...

Trade execution games in a Markovian environment ArXiv ID: 2405.07184 “View on arXiv” Authors: Unknown Abstract This paper examines a trade execution game for two large traders in a generalized price impact model. We incorporate a stochastic and sequentially dependent factor that exogenously affects the market price into financial markets. Our model accounts for how strategic and environmental uncertainties affect the large traders’ execution strategies. We formulate an expected utility maximization problem for two large traders as a Markov game model. Applying the backward induction method of dynamic programming, we provide an explicit closed-form execution strategy at a Markov perfect equilibrium. Our theoretical results reveal that the execution strategy generally lies in a dynamic and non-randomized class; it becomes deterministic if the Markovian environment is also deterministic. In addition, our simulation-based numerical experiments suggest that the execution strategy captures various features observed in financial markets. ...

Non cooperative Liquidity Games and their application to bond market trading ArXiv ID: 2405.02865 “View on arXiv” Authors: Unknown Abstract We present a new type of game, the Liquidity Game. We draw inspiration from the UK government bond market and apply game theoretic approaches to its analysis. In Liquidity Games, market participants (agents) use non-cooperative games where the players’ utility is directly defined by the liquidity of the game itself, offering a paradigm shift in our understanding of market dynamics. Each player’s utility is intricately linked to the liquidity generated within the game, making the utility endogenous and dynamic. Players are not just passive recipients of utility based on external factors but active participants whose strategies and actions collectively shape and are shaped by the liquidity of the market. This reflexivity introduces a level of complexity and realism previously unattainable in conventional models. We apply Liquidity Game theoretic approaches to a simple UK bond market interaction and present results for market design and strategic behavior of participants. We tackle one of the largest issues within this mechanism, namely what strategy should market makers utilize when uncertain about the type of market maker they are interacting with, and what structure might regulators wish to see. ...

Insider trading in discrete time Kyle games ArXiv ID: 2312.00904 “View on arXiv” Authors: Unknown Abstract We present a new discrete time version of Kyle’s (1985) classic model of insider trading, formulated as a generalised extensive form game. The model has three kinds of traders: an insider, random noise traders, and a market maker. The insider aims to exploit her informational advantage and maximise expected profits while the market maker observes the total order flow and sets prices accordingly. First, we show how the multi-period model with finitely many pure strategies can be reduced to a (static) social system in the sense of Debreu (1952) and prove the existence of a sequential Kyle equilibrium, following Kreps and Wilson (1982). This works for any probability distribution with finite support of the noise trader’s demand and the true value, and for any finite information flow of the insider. In contrast to Kyle (1985) with normal distributions, equilibria exist in general only in mixed strategies and not in pure strategies. In the single-period model we establish bounds for the insider’s strategy in equilibrium. Finally, we prove the existence of an equilibrium for the game with a continuum of actions, by considering an approximating sequence of games with finitely many actions. Because of the lack of compactness of the set of measurable price functions, standard infinite-dimensional fixed point theorems are not applicable. ...

The Specter (and Spectra) of Miner Extractable Value ArXiv ID: 2310.07865 “View on arXiv” Authors: Unknown Abstract Miner extractable value (MEV) refers to any excess value that a transaction validator can realize by manipulating the ordering of transactions. In this work, we introduce a simple theoretical definition of the ‘cost of MEV’, prove some basic properties, and show that the definition is useful via a number of examples. In a variety of settings, this definition is related to the ‘smoothness’ of a function over the symmetric group. From this definition and some basic observations, we recover a number of results from the literature. ...

Variations on the Reinforcement Learning performance of Blackjack ArXiv ID: 2308.07329 “View on arXiv” Authors: Unknown Abstract Blackjack or “21” is a popular card-based game of chance and skill. The objective of the game is to win by obtaining a hand total higher than the dealer’s without exceeding 21. The ideal blackjack strategy will maximize financial return in the long run while avoiding gambler’s ruin. The stochastic environment and inherent reward structure of blackjack presents an appealing problem to better understand reinforcement learning agents in the presence of environment variations. Here we consider a q-learning solution for optimal play and investigate the rate of learning convergence of the algorithm as a function of deck size. A blackjack simulator allowing for universal blackjack rules is also implemented to demonstrate the extent to which a card counter perfectly using the basic strategy and hi-lo system can bring the house to bankruptcy and how environment variations impact this outcome. The novelty of our work is to place this conceptual understanding of the impact of deck size in the context of learning agent convergence. ...

A Game of Competition for Risk ArXiv ID: 2305.18941 “View on arXiv” Authors: Unknown Abstract In this study, we present models where participants strategically select their risk levels and earn corresponding rewards, mirroring real-world competition across various sectors. Our analysis starts with a normal form game involving two players in a continuous action space, confirming the existence and uniqueness of a Nash equilibrium and providing an analytical solution. We then extend this analysis to multi-player scenarios, introducing a new numerical algorithm for its calculation. A key novelty of our work lies in using regret minimization algorithms to solve continuous games through discretization. This groundbreaking approach enables us to incorporate additional real-world factors like market frictions and risk correlations among firms. We also experimentally validate that the Nash equilibrium in our model also serves as a correlated equilibrium. Our findings illuminate how market frictions and risk correlations affect strategic risk-taking. We also explore how policy measures can impact risk-taking and its associated rewards, with our model providing broader applicability than the Diamond-Dybvig framework. We make our methodology and open-source code available at https://github.com/louisabraham/cfrgame Finally, we contribute methodologically by advocating the use of algorithms in economics, shifting focus from finite games to games with continuous action sets. Our study provides a solid framework for analyzing strategic interactions in continuous action games, emphasizing the importance of market frictions, risk correlations, and policy measures in strategic risk-taking dynamics. ...

How Competitive is the Stock Market? Theory, Evidence from Portfolios, and Implications for the Rise of Passive Investing ArXiv ID: ssrn-3821263 “View on arXiv” Authors: Unknown Abstract The conventional wisdom in finance is that competition is fierce among investors: if a group changes its behavior, others adjust their strategies such that noth Keywords: Market Efficiency, Investor Behavior, Game Theory, Strategic Interaction, Equities Complexity vs Empirical Score Math Complexity: 7.5/10 Empirical Rigor: 7.0/10 Quadrant: Holy Grail Why: The paper employs a semi-structural economic model with equilibrium conditions, endogenous elasticities, and formal estimation challenges (reflection problem, endogeneity), requiring advanced mathematics. It is empirically rigorous, using detailed institutional portfolio data and a novel identification strategy with instruments to estimate the demand system and the strategic response of investors. flowchart TD A["Research Goal: Quantify investor competition<br>and its implications for passive investing"] --> B["Methodology: Game-theoretic model<br>of strategic portfolio choice"] B --> C["Data: US equity market portfolios<br>1980-2015 (CRSP)"] C --> D["Computational Process:<br>Simulate competitive equilibria<br>under varying investor assumptions"] D --> E["Key Findings:<br>1. Competition is strong but incomplete<br>2. Passive investing reduces competition<br>3. Market efficiency varies with investor structure"]