Title and abstracts

Alberto Bisin
New York University, New York, USA 

Some Economics of Inequality 
Lecture 1 – Non-Stationary Wealth Dynamics and Taxation in the U.S. With an Application to the Racial Gap – with Jess Benhabib (NYU) and Mi Luo (Peking Un.)
Abstract: We estimate the parameters of a macroeconomic model of the dynamics of the distribution of wealth. We do not impose any assumption on the stationarity of the process, centering in fact on the transitional dynamics of the wealth distribution in the U.S. from 1962-63 to 2022. We show that the model, at the estimated parameter values, fits well the dynamics of the wealth distribution by accurately producing the dramatic increase in inequality observed in this period. We show how tax reforms – and how agents anticipate them – affect wealth accumulation. We identify (conditions on) future taxation processes which induce the dynamics to be stationary; that is, which lead wealth inequality to settle. Furthermore, we study the dynamics of the racial wealth gap and the relative role of stochastic earnings, differential savings, and capital income risk in driving it.

Lecture 2: The Circulation of Elites – with Thierry Verdier (Paris School of Economics) 
Abstract: We provide an abstract model of the interaction between culture and political institutions.The model is designed to study the political economy of elites and civil society on the determination of long-run socio-economic activity. We characterize conditions such that the cultural traits of elites and civil society and the institutions determining their relative political power complement (resp. substitute) each other, giving rise to a multiplier effect which amplifies (resp. dampens) their combined ability to spur socio-economic activity. We show how the joint dynamics may display hysteresis, oscillations, depending on the form of the interaction between elites and civil society.

Jean-Philippe Bouchaud
CFM and Academie des Sciences, Paris, France

Random Multiplicative Growth and Inequalities: A Rich Theoretical Framework
Abstract: Random multiplicative growth processes provide a simple yet remarkably powerful framework to understand a wide range of “scale‑free’’ phenomena, from city and firm sizes to wealth distributions. I will review how multiplicative noise generically generates Pareto (power‑law) tails. In the absence of redistribution (/migrations), the model reveals a genuine condensation transition: wealth/populations concentrates on a vanishing fraction of entities. I will then introduce a generic stochastic model in which multiplicative growth is coupled to redistribution or diffusion on a network—motivated by migration between cities, wealth taxes and transfers, portfolio rebalancing, or species flow between habitats. This framework allows one to discuss (i) the asymptotic global growth rate, (ii) the tail exponent of the stationary distribution of “abundances”, and (iii) the conditions under which redistribution prevents condensation. I will discuss the role of network topology, heterogeneity of local growth rates and their time-persistence, and show how these ingredients lead to non‑trivial “exploration–exploitation’’ trade‑offs and to an optimal tax or transfer rate. Connections with directed polymers, KPZ‑type growth, and recent applications in economics and ecology will also be outlined.

Marc Fleurbaey
CNRS and Paris School of Economics, Paris, France

Social interactions, equity and mobility

Abstract: Social interactions shape individuals and their life paths. There are various ways in which social interactions can be introduced in economic models. Two will be highlighted. One consists in adding a social interaction “game” to the economy, in a form of integrated economy-society model. The other consists in depicting how social stratification is affected by interactions in which individuals help one another. In both approaches, the duality between cooperation and competition appears essential.

Rosario N Mantegna
University of Palermo, Palermo, Italy

Lecture 1: Household stock portfolios in a national stock market: Heterogeneity of portfolios.

Lecture 2: Household stock portfolios in a national stock market: Information and wealth inequality.

Abstract: We discuss the long-term dynamics of stock portfolios ownership held by individual Finnish legal entities on the Helsinki exchange venue of Nasdaq Nordic from 2001 to 2024. The focus is on the profile of investiment on Finnish stocks of Finnish citizen. Specifically, we discuss both the nature and value of portfolios of stocks owned by each Finnish investor over 24 years. Portfolios are highly heterogenous both in composition and in value and we monitor the time evolution of heterogeneity and inequality over the considered time period. Concerning the heterogeneity of investment profiles, we use the Herfindahl-Hirschman Index (HHI) to measure portfolio concentration, analyzing individual Finnish household portfolios and how they evolve into a collective aggregated household portfolio over time. Concerning the value we follow the traditional analysis based on Lorenz curve and Gini coefficient and we also investigate the time evolution of the probability density function of the stock wealth of the population. Among Finnish retail investors, the wealthier 1% investors own from about 45% to 55% of the total stock wealth directly owned by retail investors during the period of time from 2001-04-30 to 2024-12-31. Furthermore, while male and female retail investors show similar investment patterns, women consistently exhibit higher concentration levels in their individual stock portfolios and their quota of stock wealth is less than the one of males investors.
Keywords. Behavioural finance; Heterogeneity; Inequality, Stock portfolios; Information, Financial markets.

References : [1] Milazzo, M., Musciotto, F., Piilo, J. and Mantegna, R.N., 2025. Heterogeneity of household stock portfolios in a national market. arXiv preprint arXiv:2503.17778, 2025.

André Masson
CNRS, Ecole des Hautes Etudes en Sciences Sociales, Paris School of Economics, Paris, France

Lecture 1: Conflicting ideologies and philosophies of inheritance today

Lecture 2: Is France becoming (again) a society of inheritors and how to avoid it?

Abstract of lecture 1: I shall first recall some key facts and major features of the current wealth and inheritance situation and its historical changes in France (and in Europe and the States): the growing aggregate wealth to income ratio, the aging of wealth which is more and more concentrated among senior households, and hence the booming of downward private transfers, meaning that wealth is on average more and more inherited. Yet, despite its increasing weight, inheritance is received in full property (bare property plus usufruct) much later in life today, at 60 years old on average in France. On the other hand, the wealth transfer tax, once well accepted, has become more and more unpopular, despite its limited revenue due to an increasing number of loopholes: especially in Europe in the 21^th century, a series of countries, including Sweden and quasi Italy, have suppressed the tax. Last but not least, contrary to what is often claimed, economists and philosophers do not agree at all on the proper level and progressivity, or even on the legitimacy of the wealth transfer tax.
This lack of consensus leads to the core of the presentation, which considers conflicting ideologies or philosophies of inheritance, according to the respective roles given to property rights, family values and altruism towards children, and inequality in life opportunities in wealth. The French Code civil and its evolution reflect a moral dilemma or trade-off between family morality and values on the one hand, equal citizenship or social justice on the other: the inheritance tax in France (and continental Europe) can indeed be analysed as a variable compromise between these two series of values. Finally, an explanation is given of the historical decline and the growing unpopularity of the wealth transfer tax, which has become by far the most unpopular tax whereas the annual wealth tax remains the most popular one.

Abstract of lecture 2: A society of inheritors is a society where (material) inheritance plays a crucial role in the building of wealth and is generally necessary to reach top social or financial positions. It is also a society where life without inheritance is often miserable. In that respect, France today is compared to two reference societies in the past: France during the 30 Glorious years (1947-1976), which was more of a “meritocratic” society, and France in 1900 (or also in Balzac times), which was definitely a society of inheritors and rentiers. France today stays clearly in an intermediate position and is still quite different from the 1900 society of inheritors, owing especially to the huge rise of the Social State since 1910. There are, however, worrying signs. France today could get closer to the France of 1900 owing the Great Wealth Transfer resulting from the disappearance of numerous and wealthier baby-boomers over the period 2025-2040. Moreover, it has other specific bad features, such as the fact that inheritance goes from very old individuals to already old ones.

For social reformers, there is thus an urgent need for reform of the (French) inheritance tax in order to channel the Great Wealth Transfer and reduce wealth inequalities, all the more so that the most simple and popular reform would be the overall suppression of the tax. Usual reform proposals, such as the accessions tax, do not really respond to these challenges. They do neither cope with the fact that household saving, being too short-term and little risky, cannot finance at a large scale heavy and long-term investments for the future, either productive (infrastructures), digital, ecological or social (education, health, housing). My proposal is to use a renovated inherited tax as an incentive mechanism to channel seniors’ inert saving and the Great Wealth transfer into such long-term and dynamic investment.

Antoine Parent,
Université Paris -Université Paris 8 – Sciences Po, Paris – Cliometrics And Complexity, Institut des Systèmes Complexes, Lyon

Title : Reinventing a modern form of social class theory based on income polarisation indicators. An application to the ‘yellow jackets’ social conflict France.

Abstract: Guilluy (2014) introduces the notion of “peripheral France” associated to the losers of globalization. We offer a multidisciplinary assessment of this notion. We then propose an empirical exploration of the territorial dimension of inequality and polarization indices in France. We apply Foster-Wolfson’s and Esteban and Ray’s polarization indicators to the most granular territorial level, that of the postal codes of France’s 36,000 municipalities. Income polarization indicators, a measure of social unrest in the territories, give full scope to the dimension of peripheral France as that of poverty. Ultimately, we suggest that a renewed theoretical approach to social classes based on income polarization indicators would help better apprehend the true nature of modern social conflicts.

Andrea Roventini
Scuola Superiore di Sant’Anna, Pisa, Italy

Lecture 1: Global divergence and catching-up policies in a multi-country agent-based model.

Abstract: The lecture presents a multi-country, multi-industry agent-based model in order to study the drivers and patterns of technological change and production together with the (imperfect) mechanisms of coordination among a multitude of firms. The model, rooted in evolutionary growth theory, explain the emergence of growth and persistent income divergence among countries together with a rich ensemble of empirical regularities at macro, meso and micro levels of aggregation. Finally, the model is employed to assess different strategies that laggard countries can adopt to catch up with leaders. 

Lecture 2: Inequality dynamics and economics growth in an agent-based framework.

Abstract: The lecture presents two agent-based models to study the complex relationship between economic growth and inequality dynamics, and the possible policy responses. The first model focuses on how coordination failures, credit constraints, and unequal access to investment opportunities affect inequality and income dynamics. Simulation results show that redistributive fiscal policies foster a trickle-up growth dynamics which benefits the income growth of all the agents of the economy. The second model examines the impact of access to education on distributional and macroeconomic outcomes in a meritocratic economy where households’ financial prospects and labour productivity depend on their ability to obtain education. Simulations show that predistributive policy interventions aimed at broadening educational access and reducing disparities in income can promote more inclusive economic growth and enhance social mobility.

Victor Yakovenko
University of Maryland, USA

Economic inequality from a statistical physics point of view
Abstract: Inequality is an important and seemingly inevitable aspect of the human society.  Various manifestations of inequality can be derived from the concept of entropy in statistical physics.  In a stylized model of monetary economy, the probability distribution of money among the agents converges to the exponential Boltzmann-Gibbs law due to entropy maximization.  Our analysis of empirical data shows that income distributions in the USA and other countries exhibit a two-class structure.  The lower class (about 97% of population) is characterized by the “thermal” exponential distribution, whereas the upper class (about 3%) by the “superthermal” Pareto power law.  The total income share of the upper class expands and contracts dramatically during booms and busts in financial markets.  We also found that global inequality in energy consumption and CO2 emissions has been decreasing since 1980 (likely due to the globalization) and converging toward the exponential distribution.  But this decrease in global inequality stopped recently, when maximal entropy was reached, as we predicted in advance.  All papers are available at http://physics.umd.edu/~yakovenk/econophysics/

Louis Chauvel
University of Luxembourg, Luxembourg

Lecture1: The future of income and wealth inequalities: Back to Pareto and forth to futures of societal inequality

Abstract: We are now on the Way to Extreme Inequalities. IN the last century, Vilfredo Pareto shifted the sociological focus from the Queteletian “average man” toward the extreme distributions that inspired generations of economists and mathematicians from Zipf to Gabaix to demonstrate how power-law distributions and “leptokurtic” curves (characterized by fat tails) accurately represent the modern concentration and dynamics of wealth. This “repatrimonialization” signals the end of the Western middle-class dream of social welfare, as wealth gaps increasingly outpace income growth. By applying 3D “strobiloid” visualizations, the hollowing out of the social center in favor of an elite-heavy class structure is illustrated. Ultimately, the lecture warns that these extreme mathematical realities create a self-sustaining spiral of inequality that threatens the social stability of the 21st century. 

Lecture2: The Future of Generational Inequalities: Back to Mannheim and Forth to Futures of Youth

Abstract The current social transformations experienced by young adults increasingly fit with the “Theory of Social Generations,” from Karl Mannheim’s foundational concepts of Generationengeist and Generationenlage to modern futures of systemic youth exclusion. Utilizing the “Age-Period-Cohort” (APC) toolbox, this lecture analyzes how “transitional socialization” creates durable “scar effects” that dictate the life chances of emerging cohorts. By applying innovative models, we demonstrate how multidimensional fractures (the polycrisis ranging from educational déclassement to home-ownership barriers) are hollowing out the middle-class dreams of younger generations, underlying a current global crash test of “rewealthization,” where the widening divide between wealth-poor youth and established owners threatens 21st-century social stability. Ultimately, the lecture warns that unless structural “hysteresis” is addressed, the future of youth will be defined by a permanent spiral of downward mobility.