Giulio Cimini

Associate Professor of Theoretical Physics
University of Rome Tor Vergata

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About me

I am Associate Professor of Theoretical Physics at the Physics Department of University of Rome Tor Vergata, and Research Associate at the "Enrico Fermi" research center. 

I am a statistical physicist with research interests in complex networks theory and interdisciplinary socio-economic applications. I got my PhD in Theoretical and Interdisciplinary Physics in the group of Yi-Cheng Zhang at University of Fribourg. Before my current position, I worked with Anxo Sánchez at Universidad Carlos III in Madrid as SNSF fellow, in the PIL group of Luciano Pietronero and Andrea Gabrielli at ISC-CNR in Rome, and in the NETWORKS unit at IMT Lucca with Guido Caldarelli. 

I serve in the board of the Network Science Society, the council of the Complex Systems Society and the steering committee of CCS/Italy. I am Associate Editor of Frontiers in Physics - Interdisciplinary Physics.

My current research topics are:

News

New Preprint on arXiv

M. Fessina, G. Cimini, T. Squartini, P. Astudillo-Estévez, S. Thurner, D. Garlaschelli. Inferring firm-level supply chain networks with realistic systemic risk from industry sector-level data. arXiv:2408.02467

Production networks constitute the backbone of every economic system. They are inherently fragile as several recent crises clearly highlighted. Estimating the system-wide consequences of local disruptions (systemic risk) requires detailed information on the supply chain networks (SCN) at the firm-level, as systemic risk is associated with specific mesoscopic patterns. However, such information is usually not available and realistic estimates must be inferred from available sector-level data such as input-output tables and firm-level aggregate output data. Here we explore the ability of several maximum-entropy algorithms to infer realizations of SCNs characterized by a realistic level of systemic risk. We are in the unique position to test them against the actual Ecuadorian production network at the firm-level. Concretely, we compare various properties, including the Economic Systemic Risk Index, of the Ecuadorian production network with those from four inference models. We find that the most realistic systemic risk content at the firm-level is retrieved by the model that incorporates information about firm-specific input disaggregated by sector, indicating the importance of correctly accounting for firms' heterogeneous input profiles across sectors. Our results clearly demonstrate the minimal amount of empirical information at the sector level that is necessary to statistically generate synthetic SCNs that encode realistic firm-specific systemic risk.

New Preprint on arXiv

A. Mancini, A. Desiderio, G. Palermo, R. Di Clemente, G. Cimini. The rise and fall of WallStreetBets: social roles and opinion leaders across the GameStop saga. arXiv:2403.05876

Nowadays human interactions largely take place on social networks, with online users' behavior often falling into a few general typologies or "social roles". Among these, opinion leaders are of crucial importance as they have the ability to spread an idea or opinion on a large scale across the network, with possible tangible consequences in the real world. In this work we extract and characterize the different social roles of users within the Reddit WallStreetBets community, around the time of the GameStop short squeeze of January 2021 - when a handful of committed users led the whole community to engage in a large and risky financial operation. We identify the profiles of both average users and of relevant outliers, including opinion leaders, using an iterative, semi-supervised classification algorithm, which allows us to discern the characteristics needed to play a particular social role. The key features of opinion leaders are large risky investments and constant updates on a single stock, which allowed them to attract a large following and, in the case of GameStop, ignite the interest of the community. Finally, we observe a substantial change in the behavior and attitude of users after the short squeeze event: no new opinion leaders are found and the community becomes less focused on investments. Overall, this work sheds light on the users' roles and dynamics that led to the GameStop short squeeze, while also suggesting why WallStreetBets no longer wielded such large influence on financial markets, in the aftermath of this event.

New Preprint on arXiv

A. Desiderio, L. M. Aiello, G. Cimini, L. Alessandretti. The causal role of the Reddit collective action on the GameStop short squeeze. arXiv:2401.14999

In early 2021, the stock prices of GameStop, AMC, Nokia, and BlackBerry experienced dramatic increases, triggered by short squeeze operations that have been largely attributed to Reddit's retail investors. These events showcased, for the first time, the potential of online social networks to catalyze financial collective action. How, when and to what extent Reddit users played a causal role in driving up these prices, however, remains unclear. To address these questions, we employ causal inference techniques, leveraging data capturing activity on Reddit and Twitter, and trading volume with a high temporal resolution. We find that Reddit discussions foreshadowed trading volume before the GameStop short squeeze, with their predictive power being particularly strong on hourly time scales. This effect emerged abruptly and became prominent a few weeks before the event, but waned once the community of investors gained widespread visibility through Twitter. As the causal link unfolded, the collective investment of the Reddit community, quantified through each user's financial position on GameStop, closely mirrored the market capitalization of the stock. The evidence from our study suggests that Reddit users fueled the GameStop short squeeze, and thereby Reddit served as a coordination hub for a shared financial strategy. Towards the end of January, users talking about GameStop contributed to raise the popularity of BlackBerry, AMC and Nokia, which emerged as the most popular stocks as the community gained global recognition. Overall, our results shed light on the dynamics behind the first large-scale financial collective action driven by social media users.

New Preprint on arXiv

A. Desiderio, A. Mancini, G. Cimini, R. Di Clemente. Recurring patterns in online social media interactions during highly engaging events. arXiv:2306.14735

People nowadays express their opinions in online spaces, using different forms of interactions such as posting, sharing and discussing with one another. These digital traces allow to capture how people dynamically react to the myriad of events occurring in the world. By unfolding the structure of Reddit conversations, we describe how highly engaging events happening in the society affect user interactions and behaviour with respect to unperturbed discussion patterns. Conversations, defined as a post and the comments underneath, are analysed along their temporal and semantic dimensions. We disclose that changes in the pace and language used in conversations exhibit notable similarities across diverse events. Conversations tend to become repetitive with a more limited vocabulary, display different semantic structures and feature heightened emotions. As the event approaches, the shifts occurring in conversations are reflected in the users' dynamics. Users become more active and they exchange information with a growing audience, despite using a less rich vocabulary and repetitive messages. The peers of each user fill up more semantic space, shifting the dialogue and widening the exchange of information. The recurring patterns we discovered are persistent across several contexts, thus represent a fingerprint of human behavior, which could impact the modeling of online social networks interactions.

New Paper on Physical Review E

G. Palermo, A. Mancini, A. Desiderio, R. Di Clemente, G. Cimini. Spontaneous opinion swings in the Voter Model with latency. Phys. Rev. E 110, 024313 (2024)

The cognitive process of opinion formation is often characterized by stubbornness or resistance of agents to changes of opinion. To capture this feature we introduce a constant latency time in the standard voter model of opinion dynamics: after switching opinion, an agent must keep it for a while. This seemingly simple modification drastically changes the stochastic diffusive behavior of the original model, leading to deterministic dynamical oscillations in the average opinion of the agents. We explain the origin of the oscillations and develop a mathematical formulation of the dynamics that is confirmed by extensive numerical simulations. We further characterize the rich phase space of the model and its asymptotic behavior. Our work offers insights into understanding and modeling the phenomenon of opinion swings, often observed in diverse social contexts.

New Paper on Chaos, Solitons & Fractals

M. Fessina, A. Zaccaria, G. Cimini, T. Squartini. Pattern-detection in the global automotive industry: a manufacturer-supplier-product network analysis. Chaos, Solitons & Fractals 181, 114630 (2024)

Production networks arise from supply and customer relations among firms. These systems are gaining growing attention as a consequence of disruptions due to natural or man-made disasters that happened in the last years, such as the Covid-19 pandemic or the Russia-Ukraine war. However, data constraints force the few, available studies to consider only country-specific production networks. In order to fully capture the cross-country structure of modern supply chains, here we focus on the global automotive industry as represented by the MarkLines Automotive dataset. After representing this data as a network of manufacturers, suppliers, and products, we perform a pattern-detection exercise using a statistically grounded validation technique based on the maximum entropy principle. We reveal the presence of a significantly large number of V-shaped and square-shaped motifs, indicating that manufacturing firms compete and are seldom engaged in a buyer-supplier relationship, while they typically have many suppliers in common. Interestingly, generalist and specialist suppliers coexist in the network. Additionally, we unveil the presence of geographical patterns, with manufacturers clustering around groups of suppliers; for instance, Chinese firms constitute a disconnected community, likely an effect of the protectionist policies promoted by the Chinese government. We also show the tendency of suppliers to organize their production by targeting specific functional modules of a vehicle. Besides shedding light on the self-organising principles shaping production networks, our findings open up the possibility of designing realistic generative models of supply chains, to be used for testing the resilience of the interconnected global economy.

New Paper on Scientific Reports

G. Tsekenis, G. Cimini, M. Kalafatis, A. Giacometti, T. Gili, G. Caldarelli. Network topology mapping of Chemical Compounds Space. Scientific Reports 14, 5266 (2024)

We define bipartite and monopartite relational networks of chemical elements and compounds using two different datasets of inorganic chemical and material compounds, as well as study their topology. We discover that the connectivity between elements and compounds is distributed exponentially for materials, and with a fat tail for chemicals. Compounds networks show similar distribution of degrees, and feature a highly-connected club due to oxygen. Chemical compounds networks appear more modular than material ones, while the communities detected reveal different dominant elements specific to the topology. We successfully reproduce the connectivity of the empirical chemicals and materials networks by using a family of fitness models, where the fitness values are derived from the abundances of the elements in the aggregate compound data. Our results pave the way towards a relational network-based understanding of the inherent complexity of the vast chemical knowledge atlas, and our methodology can be applied to other systems with the ingredient-composite structure.

PRIN(s) 2022 and 2022 PNRR

The projects with acronym RENet (in collaboration with Tiziano Squartini) and C2T (with Tiziano Squartini, Diego Garlaschelli and Andrea Gabrielli) have been funded by the Italian Ministry of University under the PRIN programme. Stay tuned!

Highlights

MSc in Complex Systems @Tor Vergata