Theoretical Physics News

Support for scientists and students from Ukraine

The Institute for Theoretical Physics and the Department of Physics are reaching out to scientists and students in (theoretical) physics from Ukraine to offer support, e.g. by offering office space or otherwise. Those interested are asked to contact the head of department, prof. Stefan Vandoren ( The department is also willing to consider similar requests from researchers and students who have fled Russia or Belarus.

UU talent Robin Verstraten spotted in EW Magazine: Talented 30 under 30

For ten years, EW magazine (formerly Elseviers Weekblad) has made an annual selection of 30 talents under 30. The selection consists of five categories: governance, politics, sports, science and media, and six candidates are chosen in each category. This year's selection includes 2nd MPs Julian Bushoff (PvdA) and Harmen Krul (CDA), tennis player Tallon Griekspoor, radio DJ and content creator Bram Krikke, and this year our own UU physics PhD student Robin Verstraten (26 years old). EW Magazine (… ) selects the most promising young people under 30 who will help shape the future of the Netherlands. We are proud of Robin!

That Robin has been chosen is special because he has risen from VMBO advice to PhD student. He is already well over halfway through his PhD.  Especially in secondary school, it was not easy because of dyslexia, and every year it was a fight to get into the next grade. Just look up Robin in the UU database, and under publications ( you will already see an impressive list of publications on the subject. He then started his double studies in mathematics and physics bachelor and then also double master. He even won the best thesis award from UU and GSNS in 2021 for his master's research on time glass. Now he is researching fractional derivatives in friction in quantum systems, studying how quantum mechanics works on fractals, which can have a fractional dimension. And oh yes, in addition, he will soon travel to Seoul. In South Korea, he will compete in the Rubik's cube World Championships.

The Kramers chair of Theoretical Physics

The Institute for Theoretical Physics (ITP) is excited to announce that Prof. Randall Kamien (University of Pennsylvania) will be the (visiting) Kramers Professor in February and March 2023. Prof. Kamien is an extremely versatile theoretical physicist working on soft matter, with a particular focus on the physics and the intricate geometry and topology of liquid crystals. His strong reputation and his broad knowledge across many areas of physics are also reflected by two important editorships, as he has been  Lead Editor of Journal of Modern Physics since 2017 and APS Editor in Chief (of the Physical Review series) since the beginning of 2023,  see also Prof. Kamien is also well known for his high-quality and enthusiastic lectures, and we are looking forward to his lectures on “Geometric and Topological Methods in Materials” in the D-ITP MSc-course ATTP during his visit. More information on Prof. Kamien can be found on his website During his visit, his office in the ITP will be BBG 7.84.

Nucleons in Heavy Ion Collisions Are Half as Big as Previously Expected

The initial state energy density distribution in the transverse plane for various choices of the model parameters

 Researchers from Utrecht University and MIT perform a global analysis of lead-lead collisions, finding that agreement with the reaction rate requires a much smaller nucleus.

The Science
To study atomic nuclei and subatomic particles, scientists use the Large Hadron Collider (LHC) to collide heavy ions—atomic nuclei completely stripped of their surrounding electrons. In these collisions, the quarks and gluons that normally make up nucleons (protons and neutrons) melt into a new state of matter called a quark-gluon plasma (QGP). To figure out the properties of this QGP, theorists compare a sophisticated model to a large amount of experimental data. One of the parameters in this model is the size of the nucleons inside the two colliding lead nuclei. However, to reach agreement with the reaction rate, nucleons must be smaller than scientists had expected based on previous analyses.

The Impact
Low-energy experiments find a nucleon size of around 0.5 femtometer (fm), or about 5x10-16 meters. Heavy ion collisions provide a fundamentally different perspective on the nucleon size compared to these low-energy experiments. Previous analyses of heavy ion experimental data have found a much larger nucleon size, of about 1 fm. The new analysis includes for the first time the experimentally measured reaction rate of lead-lead collisions. The reaction rate is the frequency with which atomic nuclei react with each other, and it is determined by the density of nuclei in the beam as well as the size of the nuclei. After including this reaction rate, the preferred size is around 0.6 fm, resolving the discrepancy.

The total hadronic cross section of lead-lead collisions tells scientists the collision rate for given beam density. The cross section is very easy to compute in a theoretical model, making it a good candidate for comparison to experiments in a global analysis. However, the experimental measurement is more difficult to perform. As a result, until the year 2021 scientific uncertainties on this quantity were large. In 2022, a new measurement from A Large Ion Collision Experiment (ALICE) at the LHC reduced these uncertainties substantially, allowing for its inclusion in a global analysis. This analysis, performed by researchers at the Massachusetts Institute of Technology and CERN, compares a theoretical calculation to more than 600 individual experimental data points. The analysis found that when not including the cross-section measurement, nucleon sizes of around 1 fm are preferred. However, when the cross section is included, this preferred value decreases to around 0.6 fm.

Govert Nijs
Massachusetts Institute of Technology

Wilke van der Schee
Utrecht University & CERN

Nijs, G. and van der Schee, W., Hadronic Nucleus-Nucleus Cross Section and the Nucleon Size. Physical Review Letters 129 232301 (2022). [DOI: 10.1103/PhysRevLett.129.232301]


Take a look at the ITP YouTube Channel.

ITP History

Jurriaan Wouters, PhD student at the ITP, took a dive into the early history of the Institute for Theoretical Physics, and came up with some interesting new information regarding the founding of the ITP. Read a short article on his findings.

Elisa Chisari interview in NRC

NRC published an interview with Elisa Chisari titled: Sterrenstelsels flippen om en we voelen er niks van (in Dutch)

Liquid flow reversibly creates a macroscopic surface charge gradient

Liquid flow reversibly creates a macroscopic surface charge gradient

In 2014 scientists found that the interfacial chemistry of materials is altered when water is flown over them. The discovery that flow can alter chemistry at the atomic scale was a surprise for people in the field. While the observation was already published in Science in 2014, it was still unclear why flow alters chemistry. A collaboration between ITF and the Max-Planck institute in Mainz have now found the mechanism, which was recently published in Nature Communications.

The theory shows that the chemistry of even poorly soluble minerals is already altered at low flow rates, representative of rain filtering through soil. This means that the effect could potentially be common in nature. The result could thus be relevant for geological research, affecting soil decontamination and the transport of plant nutrients in farmland.

NWO Vidi Grant for Elisa Chisari

Elisa Chisari has been awarded an NWO-VIDI grant for her research proposal "Galaxy alignments answer fundamental questions about the Universe" With the 800k€ grant Chisari and her group will investigate the physics of galaxy alignments. Galaxies are sensitive to tides across the Universe, like the ones that make the oceans on the Earth rise. In this striking phenomenon, there is a wealth of information hiding about how our Universe began, what it is made of, and how galaxies were formed. In this project, researchers will help uncover this wealth of information.

Earlier this year, Chisari received another grant to collaborate with students on developing activities for the public to inform them about light pollution and its negative effects on biodiversity in the city and its surroundings.

NWO Vici Grant for Umut Gursoy

Umut Gursoy was awarded 1,5 million euros for his NWO-VICI proposal "The most archaic ocean in our universe." 

String theory suggests that waves in an ocean of quarks and gluons—the fundamental building blocks of atomic nuclei—are related to ripples on a black-hole horizon. Gursoy and his team will use this connection to describe how energy and charge flowed in our universe microseconds after the Big Bang.

NWO-ENW-Klein grant for developing black hole on a chip

Rembert Duine (UU & TU/e) and Reinoud Lavrijsen (TU/e) received an NWO-ENW-Klein grant of 700,000 euro for the proposal 'Black Holes on a Chip'. The goal of the proposed research is to use state-of-the-art materials science and nano-fabrication techniques to experimentally realise a magnetic analogue of astronomical black holes. The underlying theory was developed by Rembert Duine and published in 2017.

More info here.