Department of Theoretical Physics

Tea Tušar (TBA)
2025-06-26 14:00 - 15:00 (Europe/Ljubljana) | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2978/

Misha Gorshteyn: Cabibbo unitarity: anomaly (dis)appears
2025-06-19 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
Unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix is one of the cornerstones of the Standard Model.
The unitarity constraint that involves the top-row matrix elements, $|V_{ud}|^2+|V_{us}|^2+|V_{ub}|^2=1$ is particularly
important because all elements are measured very precisely permitting a test at the 0.01% level. At this accuracy,
$V_{ub}sim10^{-3}$ is irrelevant, and the unitarity constraint reduces to the two-flavor Cabibbo unitarity pattern with a single
Cabibbo angle $theta_C$ and $V_{ud}=costheta_C$ and $V_{us}$. At present, a mild deficit is observed,
$|V_{ud}|^2+|V_{us}|^2=0.9985(7)$. As such, this deficit may suggest some new physics, but to make this claim all Standard
Model ingredients must be firmly under control. I review these ingredients across theory and experiment and review the most
recent developments.
https://indico.ijs.si/event/2861/

Arnau Bas i Beneito: New methods to probe Standard Model Extensions via Proton Decay and Neutrino Masses
2025-06-13 11:00 - 12:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (C/2-X – F1 čajnica)
Baryon and lepton number are excellent low-energy symmetries of the Standard Model (SM) that tightly constrain the form of its extensions. In this paper we investigate the possibility that these accidental symmetries are violated in the deep UV, in such a way that one multiplet necessary for their violation lives at an intermediate energy scale M above the electroweak scale. We write down the simplest effective operators containing each multiplet that may couple linearly to the SM at the renormalisable level and estimate the dominant contribution of the underlying UV model to the pertinent operators in the SMEFT: the dimension-5 Weinberg operator and the baryon-number-violating operators up to dimension 7. Our results are upper bounds on the scale M for each multiplet–operator pair, derived from neutrino-oscillation data as well as prospective nucleon-decay searches. We also analyse the possibility that both processes are simultaneously explained within a natural UV model. In addition, we advocate that our framework provides a convenient and digestible way of organising the space of UV models that violate these symmetries.
https://indico.ijs.si/event/3005/

Nandini Das: Peeping into dark matter scenarios - From freeze in to freeze out
2025-06-12 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
The existence of dark matter in the universe is an unavoidable fact while the nature of it still remains an unresolved mystery. We here try to explore the possibilities of having particle dark matter through different level of detection prospect. With an example from each models, we would try to sketch a brief overview towards freeze in and freeze out.
https://indico.ijs.si/event/2967/

Masayuki Imai, "From Vesicles to Synthetic Minimal Cells"
2025-06-12 14:15 - 15:15 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
Life is a self-sustaining system that continuously proliferates by synthesizing membrane molecules from external raw materials, thereby enabling vesicle growth and division. Such living systems exist in a state markedly distinct from conventional physical systems, and elucidating the fundamental differences between living and non-living matter is a critical step toward understanding the essence of living systems. However, contemporary living systems are highly complex, making it extremely challenging to directly analyze the distinctions between life and matter using current organisms. To overcome this, we have constructed a model system—a minimal cell—that captures the essential features of life. Our synthetic minimal cell is a vesicle-based system that integrates the following three functional modules: 1. Artificial metabolic system, 2. Information processing system, and 3. Self-reproduction system. Furthermore, by varying the types of membrane molecules and genetic polymers, we have constructed eight distinct minimal cell types. By comparing their growth rates (fitness), we are developing a system in which the dynamics of evolution due to competition among minimal cells can emerge. In this seminar, we will introduce our synthetic minimal cell research and examine the conditions required for sustained proliferation and evolution from the perspective of non-equilibrium dynamics and information thermodynamics. This approach aims to shed light on the physical origin of the fundamental distinction between life and non-life.
https://indico.ijs.si/event/2975/

Yutaro Shoji: Regularization of Functional Determinants of Radial Operators via Heat Kernel Coefficients
2025-06-05 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
The leading order quantum corrections in quantum field theory appear in the form of functional determinants, and their evaluation is very important in theoretical and phenomenological studies. We propose an efficient regularization method using the heat kernel coefficients. It enables us to regularize functional determinants in higher dimensions. In particular, our explicit formulas can regularize functional determinants in up to 13 dimensions, which has been a very difficult task before our study. The formulas can also be used to approximate higher angular momentum contributions in lower dimensions, which makes the numerical computation very efficient. The large angular momentum expansion of our formula gives the WKB formulas in the previous studies, but extended to higher orders. The results are obtained in both the zeta function regularization and the dimensional regularization.
https://indico.ijs.si/event/2974/

Motoo Suzuki: Small Instantons and the Post-Inflationary QCD Axion in a Special Product GUT
2025-05-29 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
In this talk, after some review of axion physics, I would like to discuss our recent work about a new framework of grand unification that is equipped with an axion solution to the strong CP problem without a domain wall problem when the Peccei–Quinn (PQ) symmetry is spontaneously broken after inflation. Our grand unified theory (GUT) is based on a symmetry breaking pattern, SU(10) ×SU(5)1 →SU(5)V ⊃SU(3)C ×SU(2)L ×U(1)Y, where SU(5)1 and a special embedding of SU(5)2 ⊂SU(10) are broken to a diagonal subgroup SU(5)V. The model contains a vector-like pair of PQ-charged fermions that transform as (anti-)fundamental representations under SU(10), so that the domain wall number is one. However, after the GUT symmetry breaking, the number of vector-like pairs of PQ-charged colored fermions is larger than one, which seems to encounter the domain wall problem. This apparent inconsistency is resolved by small instanton effects on the axion potential which operate as a PQ-violating bias term and allow the decay of domain walls. We propose a domain-wall-free UV completion for an IR model where the domain wall number appears larger than one. The model gives a prediction for a dark matter axion window, which is different from that of the ordinary post-inflationary QCD axion with domain wall number one.
https://indico.ijs.si/event/2901/

Anže Božič, "Complexity of RNA sequences"
2025-05-29 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2913/

Marko Malezic: Toward Efficient Trotter-Suzuki Schemes for Long-Time Quantum Dynamics
2025-05-20 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
Accurately simulating long-time dynamics of quantum many-body systems—whether in real or imaginary time—is a challenge in both classical and quantum computing due to the accumulation of Trotter errors. While low-order Trotter-Suzuki decompositions are straightforward to implement, their rapidly growing error limits access to long-time observables and ground state properties. I will present a framework for constructing efficient high-order Trotter-Suzuki schemes by identifying their structure and directly optimizing their parameters over a high-dimensional space. This method enables the discovery of new schemes with significantly improved efficiency compared to traditional constructions, such as those by Suzuki and Yoshida. I will demonstrate the effectiveness of these decompositions on the Heisenberg XXZ model, comparing their performance and presenting the newly discovered schemes. Finally, I will discuss ongoing efforts to extend this framework to even higher orders and apply the derived schemes to quantum hardware, pushing the boundaries of both theoretical advancements and practical quantum computing.
https://indico.ijs.si/event/2921/

Angelo Rosa, "Configurational entropy of random trees"
2025-05-08 14:15 - 15:15 | Seminar room of physics (106) (IJS)
In this talk, I will illustrate two recent results of our group concerning the statistical physics of branched polymers. In the first part, I will present a graph theoretical approach to the configurational statistics of random tree-like objects, which is based on Prüfer labelling. The method, in particular, provides: (i) direct access to the exact configurational entropy as a function of the tree composition, (ii) computable exact expressions for partition functions and important experimental observables for tree ensembles with controlled branching activity and (iii) an efficient sampling scheme for corresponding tree configurations and arbitrary static properties. Then, in the second part, I will introduce a field-theoretic framework for branched polymers with excluded volume interactions. By solving the corresponding partition function by mean-field methods, I will show that the theory is in semi-quantitative agreement with Monte-Carlo computer simulations.
https://indico.ijs.si/event/2878/

Yue Zhang: Neutrino Self-interaction: Motivations and Future Probes
2025-04-29 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (C/2-X – F1 čajnica)
Neutrino self-interaction with a larger “Fermi constant” is often resorted for understanding puzzles of our universe. I will first discuss how novel neutrino self-interactions can save the sterile neutrino dark matter produced through early universe oscillation mechanism, which is otherwise ruled out by cosmological observations. The explanation requires the existence of a light scalar boson that couples exclusively to neutrinos and sets a well-motivated target for experimental probes. In the second part of talk, I will review existing constraints on the neutrinophilic scalar, and point out pathways for testing the model in upcoming experiments.
https://indico.ijs.si/event/2582/

Matej Kanduč, "Microplastics through the lens of physics"
2025-04-24 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
Micro- and nanoplastics have emerged as persistent and pervasive pollutants, raising concerns across environmental and biological systems. In this talk, I will show how we can use ideas from soft matter physics, especially colloid and interface science, to better understand how these particles behave. We will look at how nano- and microplastics act like colloids and how their movement and interactions depend on their surface properties and the conditions around them.
https://indico.ijs.si/event/2858/

Jonathan Kriewald: Lepton Number Violation at the LHC
2025-04-17 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
Numerous well-motivated extensions of the Standard Model, notably models linked to the generation of neutrino masses and to searches for neutrinoless double-beta decay, predict the existence of lepton-number-violating (LNV) processes. In particular, the type II seesaw and the left-right symmetric model predict final states consisting of same-sign di-leptons with jets and/or the existence of long-lived heavy neutral leptons which could be detected at the LHC.
In this talk I will review current collider limits on such scenarios and estimate the corresponding future HL-LHC sensitivities for these models. I will show that these models predict observable signals across broad regions of parameter space, whereas the LHC can indirectly probe New Physics scales as high as 70-80 TeV.
https://indico.ijs.si/event/2903/

Fran Ivan Vrban, "Variational model shapes of deformable particles"
2025-04-17 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2782/

Sascha Ollertz, "Agent-based modelling of cell differentiation patterns in mouse blastocysts"
2025-04-10 12:30 - 13:30 | C/2-X – F1 čajnica (Jamova)
Early embryonic development from zygote to blastocyst is a highly dynamic, self-organised process in which stem cells undergo successive cell fate decisions and form a complex structure. Local patterns in the early and mid blastocyst stage resolve into global patterns in the late stage of the blastocyst . A first modelling approach, based on cell division and signalling showed that the spatial cell fate patterns arising in the earlyand mid stage, are compatible with signalling beyond the nearest neighbours . As a next step, we expanded our existing mathematical, agent-based model to incorporate the late stage by including cell sorting based on differential adhesion. The resulting model consists of cell division, cell death, physical interactions, transcription and signalling between the cells. The model allows us to systematically investigate the influence of these mechanisms and their relative timing with respect to the formation of the global pattern in the late blastocyst stage.
Fischer, S. C., Corujo-Simon, E., Lilao-Garzon, J., Stelzer, E. H. K., & Muñoz-Descalzo, S. (2020). The transition from local to global patterns governs the differentiation of mouse blastocysts. PloS one, 15(5), e0233030.
Fischer, S. C., Schardt, S., Lilao-Garzón, J., & Muñoz-Descalzo, S. (2023). The salt-and-pepper pattern in mouse blastocysts is compatible with signaling beyond the nearest neighbors. In iScience (Vol. 26, Issue 11, p. 108106).
Schardt, S., & Fischer, S. C. (2023). Adjusting the range of cell-cell communication enables fine-tuning of cell fate patterns from checkerboard to engulfing. Journal of mathematical biology, 87(4), 54.
https://indico.ijs.si/event/2746/

Stephane Jedele, "Study of the KCNN4 channel involved in the pathological dehydration of red blood cells using molecular modeling approaches"
2025-04-09 12:15 - 13:15 | C/2-X – F1 čajnica (Jamova)
KCNN4 is a calcium (Ca)-activated potassium (K+) channel translocating K+ ions across several cellular membranes and for which Ca2+ sensitivity is conferred by calmodulin (CaM). Until the main part of the protein structure bound to CaM has been resolved, in silico studies had used homology models derived from the well characterized transmembrane domain of other K+ channels, limiting the functional investigation to this particular region. Thus, how the regulatory domains of KCNN4 communicate with each other and where the possible gates are located across the complete structure are still not well understood. My PhD work presents for the first time results obtained from an extensive investigation of full-length models of the channel in different conformational states and molecular contexts using all-atom molecular dynamics simulations and enhanced sampling methods. The results allow us to contextualize no less than 6 of the pathogenic mutations identified in the channel to date, and provide a new basis for understanding the KCNN4 function.
https://indico.ijs.si/event/2866/

Borut Bajc: E6
2025-04-08 14:00 - 15:00 | C/2-X – F1 čajnica (Jamova)
I will motivate the use of E6 grand unified theory and describe a
realistic E6 GUT which gives rise to novel possible intermediate stages.
https://indico.ijs.si/event/2874/

Sifan Yin, "Developmental mechanics of divergent buckling patterns in chick gut"
2025-03-27 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2785/

Marko Popovic, "Biological tissues as active amorphous solids"
2025-03-25 14:00 - 15:00 | C/2-X – F1 čajnica (Jamova)
https://indico.ijs.si/event/2784/

Petr Šulc, "DNA and RNA nanotechnology: molecular computing, therapeutics, and the quest for the holy grail of self-assembly"
2025-03-20 14:15 - 15:30 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
The control over the self-assembly of complex structures is a long-standing challenge of biomimetic nanotechnology, as the desired assembly pathway is often kinetically derailed by the formation of competing alternative structures or amorphous aggregates. The goal of inverse design problem is hence to find a set of blocks that reliably assemble in high yield into a target structure while avoiding kinetic traps and alternative competing states. We present here a framework called SAT-assembly, which solves this problem by combination of multiscale molecular simulation, graph theory, and constrained optimization methods. While the general approach is abstract, the proposed designs can be realized experimentally e.g. with building blocks made out of DNA or RNA strands. We then show how our models are used to guide experimental realization of highly coveted nanostructure shapes with applications ranging from therapeutic delivery to nanoscale templating, including designs such as capsids, diamond lattices, 3D polycube assemblies, and dynamic reconfigurable multifarious structures, which can switch between multiple possible stable folds.
https://indico.ijs.si/event/2744/

V. S. Rao Jampani, "Self-shaping liquids"
2025-03-13 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2745/

Enrico Morgante: Gravitational waves from confinement in improved holographic QCD
2025-03-06 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
I will discuss gravitational waves produced during the confinement phase transition in SU(N) Yang-Mills, using a holographic description. The key ingredient will be the construction of the effective action, with the kinetic term playing an important role.
https://indico.ijs.si/event/2680/

Jonathan Ron, "Deterministic cell motility patterns across scales and sizes"
2025-03-06 14:15 - 15:15 | Seminar room of physics (106) (IJS)
Cell motility plays a crucial role in various biological processes, such as embryogenesis, wound healing, and immune response. Although the complex molecular machinery driving cell motility is relatively well understood, it remains unclear how cells exhibit such diverse migration patterns, both individually and collectively. This seminar will focus on a recently developed theoretical framework for cellular migration, which couples migration features such as polarization, speed, and size to traction forces and adhesion dynamics. The discussion will begin with the model’s predictions for one-dimensional migration of single cells, emphasizing how symmetry is broken during directional decision-making. The model will then be extended to describe cell-cell interactions and the collective behavior of one-dimensional multicellular trains. A two-dimensional stochastic version of the model will also be introduced, explaining the run-and-tumble behavior commonly exhibited by cells. Finally, a new theory will be introduced, linking cell migration to volume regulation via active ion transport. The results presented in the seminar will be supported by extensive experimental validation conducted on various cell types.
Ron, J.E., Monzo, P., Gauthier, N.C., Voituriez, R. and Gov, N.S., 2020. One-dimensional cell motility patterns. Physical review research, 2(3), p.033237.
Mukherjee, A., Ron, J.E., Hu, H.T., Nishimura, T., Hanawa‐Suetsugu, K., Behkam, B., Mimori‐Kiyosue, Y., Gov, N.S., Suetsugu, S. and Nain, A.S., 2023. Actin Filaments Couple the Protrusive Tips to the Nucleus through the I‐BAR Domain Protein IRSp53 during the Migration of Cells on 1D Fibers. Advanced science, 10(7), p.2207368.
Ron, J. E., d’Alessandro, J., Cellerin, V., Voituriez, R., Ladoux, B., & Gov, N. S. (2023). Polarization and motility of one-dimensional multi-cellular trains. Biophysical Journal, 122(23), 4598-4613.
Ron, J. E., Crestani, M., Kux, J. M., Liu, J., Al-Dam, N., Monzo, P., … & Gov, N. S. (2024). Emergent seesaw oscillations during cellular directional decision-making. Nature Physics, 20(3), 501-511.
https://indico.ijs.si/event/2691/

Michael Zantedeschi: On the fate of evaporating black holes: how the burden of their memory stabilizes them
2025-02-27 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
The “memory burden” effect describes how an object’s stored information resists its own decay. This effect is especially pronounced in “saturons”—systems with maximal entropy consistent with unitarity—of which black holes are prime examples. I will show how this memory burden can halt Hawking evaporation, stabilizing black holes against complete decay. Importantly, this mechanism is not limited to gravitational systems: it also appears in renormalizable field theories. To illustrate its broader relevance, I will present a soliton model that shares key features with black holes and is similarly stabilized by its memory content. Finally, I will discuss unique phenomenological implications and potential observational signatures, particularly for dark matter scenarios.
https://indico.ijs.si/event/2637/

Nicklas Ramberg: Unveiling Hidden Sectors with Gravitational Waves ("The Gravitational Wave Stairway")
2025-02-20 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
In this talk we explore the potential of gravitational wave (GW) observations to probe the structure of hidden sectors beyond the Standard Model (BSM). We argue that the sequential decoupling of new degrees of freedom in these sectors can leave a distinctive imprint on the GW spectrum, resembling a “stairway” pattern. We investigate how this signature can distinguish between different hidden sectors, focusing on two benchmark scenarios: a dark QCD-like theory and a model with a Kaluza-Klein (KK) tower of states. We analyze the sensitivity of current and future GW detectors, such as LISA and Einstein Telescope, to these multi-step spectral features, demonstrating the potential to uncover rich information about the particle content and dynamics of hidden sectors.
https://indico.ijs.si/event/2500/

Matej Krajnc, "Hybrid mechanical model of epithelia supported by substrate"
2025-02-20 14:15 - 15:15 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2778/

Alessandro Dondarini: Constraining the Minimal Dark Matter 5-plet with Indirect Detection
2025-02-13 15:30 - 16:30 | https://zoom.us/j/3601731049?pwd=[REDACTED] (A/1-106 – Seminarska soba fizike (F5))
We critically reassess the Minimal Dark Matter model and propose new indirect detection signatures. Specifically, for the originally proposed accidentally stable SU(2) 5-plet, we compute the photon flux arising from Dark Matter Bound State Formation and Sommerfeld Enhancement, highlighting the appearance of several spectral lines. After analyzing the key features of this flux, we explore the constraints on the 5-plet imposed by FERMI-LAT observations of the galactic diffuse emission, as well as the projected sensitivity of the upcoming Cherenkov Telescope Array (CTA) in searches targeting Dwarf Spheroidal Galaxies.
https://indico.ijs.si/event/2639/

Primož Ziherl, "Soft cells and the geometry of sea shells"
2025-01-30 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2689/

Matej Kanduč, "On foam stability"
2025-01-16 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
Soft, light, and visually captivating, liquid foams are enigmatic – complex systems with intricate multiscale structures. Beneficial in some cases and undesired in others, their inherent instability raises a critical question: how can we stabilize foams? In this seminar, I will discuss our current understanding of foam decay and strategies to enhance foam stability.
https://indico.ijs.si/event/2638/

XBW rehearsal
2024-12-12 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
Speakers:Fran Ivan VrbanVeronika BukinaMarin Šako
https://indico.ijs.si/event/2562/
