CEU Department of Network and Data Science

19/10/2026

🧩 How does the organization of groups shape collective transitions?

We’re proud to share a new paper by our colleague Federico Malizia, together with Andrés Guzmán, Federico Battiston and István Z. Kiss, published in Physical Review Letters.

Using hypergraphs, the study shows that even when each individual participates in the same number of interactions, how those interactions are organized matters. For example, individuals may interact in pairs, while some of those pairs are also embedded within larger groups. The authors quantify this organization through nestedness.

Increasing nestedness promotes an earlier onset of collective behavior while making abrupt, discontinuous (or “explosive”) transitions less likely. In other words, the organization of interactions can affect not only when collective behavior emerges, but also how the transition takes place.

The paper goes beyond identifying this phenomenology. Using an analytically tractable SIS model with pairwise and three-body interactions, the authors uncover its microscopic origin: pairwise interactions embedded within larger groups accelerate early-stage spreading, while at the same time making pairwise and higher-order transmission channels increasingly redundant.

The figure illustrates how increasing nestedness reorganizes pairwise interactions into group-embedded routes, anticipating collective onset while suppressing abrupt transitions. It also shows that the same phenomenology persists across different interaction orders and dynamical processes, including SIS spreading, higher-order Ising dynamics, and synchronization models.

This project began when Federico joined DNDS, in collaboration with his former research group at Northeastern University London.

Congratulations to the authors! We also thank the anonymous PRL reviewers for their careful evaluation and valuable contribution to this work.

“Nested hyperedges promote the onset of collective transitions but suppress explosive behavior”
https://journals.aps.org/prl/abstract/10.1103/rvlj-fmf9

06/10/2026

🎓 Congratulations to Lorenzo Betti on successfully defending his doctoral dissertation in Network Science at CEU on September 11!

In “Group Dynamics in Social Systems: From Individual Behavior to Collective Organization,” Lorenzo explores how individual interactions give rise to collective organization, from open-source software teams to groups of wild birds. His research combines empirical data with network methods to uncover how groups form, function, and change over time.

We thank his dissertation committee:

🔹 János Kertész (CEU), Chair
🔹 Federico Battiston (CEU), Supervisor
🔹 Andrea Baronchelli (City University of London), Reviewer
🔹 Josefine Bohr Brask (University of Copenhagen), Reviewer

We’re delighted that Lorenzo is continuing with us as a postdoctoral researcher.

📚 Lorenzo’s dissertation will be available through the CEU Library once processing is complete: https://bit.ly/4e4y5uv

02/10/2026

🤝 The way we interact shapes the way we cooperate.

Why does cooperation thrive in some groups and struggle in others?

In a new paper published in Physical Review E, Jaume Llabrés Rubio, Onkar Sadekar, Federico Malizia, and Federico Battiston explore how cooperation emerges when people interact in groups of different sizes.

The study shows that combining group sizes with different patterns of collective returns can generate alternative collective states: full cooperation or persistent coexistence between cooperators and free riders. The organization of groups and which individuals initially cooperate also play a key role in determining which collective state emerges.

📄 “Emergence of cooperation in nonlinear higher-order public goods games”
🔗 https://doi.org/10.1103/54zg-75zk

30/09/2026

Six new faces, a new chapter! Meet our incoming PhD cohort at CEU’s Department of Network and Data Science.

A warm welcome to our six new doctoral students! Pictured from left to right:

Standing: Sara Fürnkranz, Ester Cima, George Okello Ouma
Sitting: Giacomo Tittarelli, Ali Valiyev, Athul George

We’re delighted to have you join our community and look forward to the ideas, questions, and discoveries you’ll bring.

Wishing you a rewarding start to your doctoral studies—with inspiring conversations, fruitful collaborations, and good friendships along the way. 📚✨

Image credit: CEU / Daniel Vegel, VEGEL Photo Video

25/09/2026

🎓 Congratulations to Leonardo Rizzo on his PhD defense!

On September 4, Leonardo defended his dissertation, 𝗡𝗲𝘁𝘄𝗼𝗿𝗸 𝗦𝘁𝗿𝘂𝗰𝘁𝘂𝗿𝗲𝘀 𝗮𝗻𝗱 𝗜𝗻𝗻𝗼𝘃𝗮𝘁𝗶𝗼𝗻 𝗗𝘆𝗻𝗮𝗺𝗶𝗰𝘀, at CEU’s Department of Network and Data Science.

His research explores how network structures shape innovation, coordination, and selection across organizational, institutional, and evolutionary settings. Bringing together six articles, the dissertation combines empirical network analysis, agent-based computational modeling, and methodological work to study networks as both social structures and representations of innovation spaces.

The dissertation was supervised by János Kertész, with Mark Wittek chairing the committee and Leon Oerlemans (Tilburg University) and Guido Fioretti (University of Bologna) serving as external reviewers.

Congratulations, Leonardo, on this important milestone!

22/04/2026

Join us this Friday (April 24) at the 𝗟𝗼𝗻𝗴 𝗡𝗶𝗴𝗵𝘁 𝗼𝗳 𝗥𝗲𝘀𝗲𝗮𝗿𝗰𝗵.

Elisa Omodei will present 𝘏𝘰𝘸 𝘋𝘰 𝘚𝘤𝘪𝘦𝘯𝘵𝘪𝘴𝘵𝘴 𝘜𝘴𝘦 𝘠𝘰𝘶𝘳 𝘋𝘪𝘨𝘪𝘵𝘢𝘭 𝘍𝘰𝘰𝘵𝘱𝘳𝘪𝘯𝘵𝘴 𝘵𝘰 𝘚𝘵𝘶𝘥𝘺 𝘚𝘰𝘤𝘪𝘢𝘭 𝘐𝘴𝘴𝘶𝘦𝘴?, exploring how mobile phone and social media data can help uncover patterns in human behavior, inequality, and online polarization.

The talk takes place at Central European University in Vienna and is open to a wide audience.

Learn more:

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