Department of Theoretical Physics

Ana M. Teixeira: TBA
2023-04-06 11:15 - 12:15 (Europe/Ljubljana) | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
https://indico.ijs.si/event/1569/

Florian Goertz: TBA
2023-04-06 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
https://indico.ijs.si/event/1613/

[Biophysics journal club] Matej Kanduč, "The mystery of nanobubbles: How come they exist?"
2023-04-13 14:00 - 15:00 | Seminar room of physics (106)
The industry of nanoscopic bubbles is booming. Nanobubbles are used in various industries, from agriculture and water treatment to humane medicine. Yet, in the academic world, the existence of nanobubbles has attracted both skepticism and intrigue since classical theory predicts that gas bubbles cannot achieve stable equilibrium. Can we prove these gaseous domains exist, and if they do, how do they survive? I will review contemporary theoretical perspectives on the stability of nanobubbles and explain how experiments either vindicate or disprove them.

The meeting will take place in the seminar room of physics (106).

Yutaro Shoji: TBA
2023-04-20 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
https://indico.ijs.si/event/1600/

[Biophysics seminar] Domen Vaupotič, "Analiza razvejenosti genomov virusov RNA"
2023-04-20 14:00 - 15:00 | Seminar room of physics (106)

Paolo Benincasa
2023-04-27 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
https://indico.ijs.si/event/1608/

Ben Stefanek
2023-05-04 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
https://indico.ijs.si/event/1609/

Elena Santopinto: TBA
2023-05-11 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
TBA
https://indico.ijs.si/event/1595/

Jonathan Kriewald: Heavy Neutrino effects on leptonic Higgs, $W$ and $Z$ decays in the inverse seesaw
2023-05-18 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
In addition to their role in well-motivated mechanisms of neutrino mass generation, heavy neutral leptons (HNL) can be at the source of an extensive array of new phenomena, which are forbidden (or strongly suppressed) in the Standard Model (SM), several manifesting the possible Majorana nature of the extended neutral lepton sector.
These phenomena include lepton number violating (LNV) processes such as (semi) leptonic tau and meson decays, charged lepton flavour violating (cLFV) transitions (including radiative and three-body decays, $Z$ and Higgs bosons decays, as well as rare phenomena in the presence of matter).
Such heavy Majorana fermions are also expected to have a significant
impact concerning electroweak (EW) precision observables, and also lead to striking signatures at colliders (be it the LHC, or future lepton colliders). All the above new phenomena are rooted in the non-negligible mixings of the heavy Majorana states with the light active neutrinos, which in turn is responsible for modifying the flavour mixings in the lepton sector.
Within the framework of the inverse seesaw mechanism, we calculate the electroweak corrections to leptonic Higgs, $W$ and $Z$ decays, which are modified due to the presence of HNL in the loop diagrams.
In certain regions of the currently viable parameter space significant deviations from the SM predictions can be observed.
In view of the anticipated increased precision of experimental measurements of these decay modes at future $Z$ factories (such as FCC-ee), precision measurements of leptonic Higgs, $W$ and $Z$ decays can lead to complementary constraints on seesaw-like neutrino mass models.
https://indico.ijs.si/event/1597/

Urška Andrenšek: "On the importance of thickness modulation in epithelial tissues"
2023-05-18 14:00 - 15:00 | Seminar room of physics (106) (IJS)
https://indico.ijs.si/event/1642/

Horacio Guzman: RNA fragment adsorption onto membranous surfaces of Lipid Nanoparticles"
2023-05-24 14:00 - 15:00 | Z9/0-0 – F1 čajnica (Jamova)
Lipid nanoparticles (LNPs) are promising delivery tools for mRNAs vaccines due to their ability to protect and carry mRNA to target cells. However, designing effective LNPs for mRNA delivery systems remains a challenge due to a lack of understanding of structure–activity relationships onto the membranous surfaces, which are lipid dependent, among other environment conditions(ions and pH). Here we present the influence of the membrane composition on the adsorption and stability of the RNA molecules. Our extensive analysis points out key design rules for predicting the interaction of RNA and membrane surfaces and their implications on ensembles stability.
https://indico.ijs.si/event/1640/

Pietro Baratella: Thermodynamics from scattering data
2023-05-25 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
In this seminar I will present a method for expressing thermodynamic quantities in terms of scattering amplitudes. After reviewing the classical derivation by Dashen, Ma and Bernstein, I will provide several checks of the method at leading order. The systematic inclusion of higher-order effects is then discussed, with emphasis on their natural organization in terms of a virial expansion. I will then compare the method to other existing ones and consider possible applications.
https://indico.ijs.si/event/1614/

Fran Ivan Vrban: "Photon-photon scattering under Lorentz invariance violation"
2023-05-25 14:00 - 15:30 | Seminar room of physics (106) (IJS)
https://indico.ijs.si/event/1677/

Tanmoy Sarkar: "Graph vertex model"
2023-06-06 14:00 - 15:00 | Z9/0-0 – F1 čajnica (Jamova)
I will present a new approach to studying epithelial mechanics, which is based on representing the tissue structure by a graph. Additionally, I will demonstrate the implementation of this approach within a custom computational framework, neoVM.
https://indico.ijs.si/event/1645/

Purushottam Sahu: Neutrinoless double beta decay in a left-right symmetric model with a double seesaw mechanism
2023-06-08 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
We discuss a left-right (L-R) symmetric model with the double seesaw mechanism at the TeV scale generating Majorana masses for the active left-handed (LH) flavour neutrinos$ u_{alpha L}$ and the heavy right-handed (RH) neutrinos $N_{beta R}$, $alpha,beta = e,mu,tau$, which in turn
mediate lepton number violating processes, including neutrinoless double beta decay. The Higgs sector is composed of two Higgs doublets $H_L$, $H_R$ and a bi-doublet $Phi$. The fermion sector has the usual for the L-R symmetric models quarks and leptons, along with three $SU(2)$ singlet fermion $S_{gamma L}$. The choice of bare Majorana mass term for these sterile fermions induces large Majorana masses for the heavy RH neutrinos leading to two sets of heavy Majorana particles $N_j$ and $S_k$, $j,k=1,2,3$, with masses $m_{N_j} ll m_{S_k}$. Working with a specific version of the model in which the $ u_{alpha L} – N_{beta R}$ and the $N_{beta R} – S_{gamma L}$ Dirac mass terms are diagonal, and assuming that $m_{N_j} sim (1 – 1000)$ GeV and ${rm max}(m_{S_k}) sim (1 – 10)$ TeV, $m_{N_j} ll m_{S_k}$, we study in detail the new “non-standard” contributions to the $0 ubetabeta$ decay amplitude and half-life arising due to the exchange of virtual $N_j$ and $S_k$. We find that in both cases of NO and IO light neutrino mass spectra, these contributions are strongly enhanced and are dominant at relatively small values of the lightest neutrino mass $m_{1(3)} sim (10^{-4} – 10^{-2})$ eV over the light Majorana neutrino exchange contribution. In large part of the parameter space, the predictions of the model for the $0 ubetabeta$ decay generalised effective Majorana mass and half-life are within the sensitivity range of the planned next generation of neutrinoless double beta decay experiments LEGEND-200 (LEGEND-1000), nEXO, KamlAND-Zen-II, CUPID, NEXT-HD.
https://indico.ijs.si/event/1692/

Biophysics Journal Club: Veronika Bukina, "Mexican jumping beans exhibit diffusive motion"
2023-06-15 14:00 - 15:00 | Seminar room of physics (106) (IJS)
American physicists investigated the statistical properties of the movements of Mexican jumping beans (the so-called boxes of Sebastiania pavoniana, which set the larvae of the leaflet growing in them in motion) in the absence of a temperature gradient. It turned out that in this case the motion is well described by the random walk model. The authors showed that such a strategy is more successful in finding the shadow than blind directional movement.
https://indico.ijs.si/event/1643/

Santiago Tanco: Exploring unsupervised top tagging using Bayesian inference
2023-06-15 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
Identifying hadronically decaying top-quark jets in a sample of jets is an important task in many LHC searches. Although there are outstanding supervised algorithms, their construction and expected performance rely on Monte Carlo simulations. After introducing the general framework of Bayesian inference over mixture models, I will present some results on the development of two simple unsupervised top tagging algorithms based on these techniques.
https://indico.ijs.si/event/1691/

Biophysics Journal Club: Marin Šako, "Tensile strength of water with organic impurities"
2023-06-22 14:00 - 15:00 | Z9/0-0 – F1 čajnica (Jamova)
https://indico.ijs.si/event/1648/

Fabio Staniscia, "Tolman length and anomalous adsorption at curved interfaces"
2023-06-29 14:00 - 15:00 | Z9/0-0 – F1 čajnica (Jamova)
We investigate, by using molecular dynamics simulations, the effect of curvature on the interfacial properties of pure water and water-alcohol solutions. For the pure water case we can calculate the Tolman length, which characterizes the dependence of surface tension on curvature, using different methods, while in the case of solutions, we show that curvature affects also the adsoprtion propetries. We interpret these results as an effect of Tolman length.
https://indico.ijs.si/event/1646/

Arghyadip Mukherjee: "Topological interactions drive spindle orientation and the fate decision in the Drosophila embryo"
2023-07-10 14:00 - 15:00 | Z9/0-0 – F1 čajnica (Jamova)
During embryogenesis, the earliest cell fate decision is tightly linked to nuclear positioning. Control of nuclear positioning arises from the integration of the different phases of activity during the cell cycle and associated cytoskeletal mechanics. Yet, the mechanisms that ensure that the correct number of nuclei move to the appropriate place remain poorly understood. We discover that in the syncytial blastoderm of Drosophila embryos spindle orientation controls which nuclei migrate towards the cortex and which ones remain inside the embryo, determining the eventual fate of the nuclei and the number of cells undergoing development. Using cytoskeletal mechanics and arguments describing the behaviour of space-filling systems, we develop a minimal theory for aster-aster interactions in an aster aggregate. Combining theoretical predictions and computational methods inspired by integral geometry with mutations in cell cycle genes, we show that spindle orientation is controlled by topological aster-aster interactions and is scale independent. Our work reveals general principles that underlie interplay between cytoskeletal mechanics with geometry and topology and how that uniquely affects density homeostasis and cell fate determination.
https://indico.ijs.si/event/1700/

Emanuel Schneck: "Investigating Biomembrane Models at Fluid Interfaces—from Bacteria Surfaces to Glycolipid Domains to RNA delivery"
2023-07-20 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
Biological membranes based on lipid bilayers are major components of all living organisms, but lipid layers are also used in many biomedical applications. We use biomembrane models in the form of lipid mono- and bilayers at water/air and water/oil interfaces in order to investigate various biological and biotechnologically relevant phenomena involving lipid layers. These experimental models are comprehensively characterized with numerous surface-sensitive techniques, notably x-ray and neutron scattering/reflectometry and x-ray fluorescence, as well as molecular dynamics simulations. The talk will cover examples from our recent activities, including the conformation of wild-type bacterial lipopolysaccharide layers , the formation of glycolipid-enriched ordered lipid domains , the characteristics of lipid bilayers adsorbed to functionalized fluid interfaces , and the pH-dependent charge and structural properties of transfection lipid layers for RNA delivery. S. Micciulla, Y. Gerelli, E. Schneck; Biophysical Journal, 2019, 116, 1259. T. Mukhina, G. Brezesinski, C. Shen, E. Schneck; J. Colloid Interf. Sci., 2022, 615, 786. J. Pusterla, E. Scoppola, C. Appel, T. Mukhina, C. Shen, G. Brezesinski, E. Schneck; Nanoscale 2022, 14, 15048.
https://indico.ijs.si/event/1701/

Ahmed Youssef: MLHAD: A Machine Learning based Simulation for Hadronization
2023-08-03 11:00 - 12:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
Hadronization, a crucial component of event generation, is traditionally simulated using fine-tuned empirical models. While current phenomenological models have been quite successful overall in simulating this process, there are still areas where they lack accuracy in describing the underlying physics. In this talk, I will introduce MLHAD, a proposed alternative that replaces the empirical model with a surrogate machine learning-based approach, ultimately enabling data-trainability. I will detail the current stage of development and discuss possible future directions.
https://indico.ijs.si/event/1722/

Prospecting for new physics using muons
2023-08-10 11:00 - 12:00 | Z9/0-0 – F1 čajnica (Jamova)
Speakers: Jure Zupan (University of Cincinnati)
https://zoom.us/j/3601731049?pwd=[REDACTED]
https://indico.ijs.si/event/1723/

Liam Scarratt: " Probing Aqueous Nanofluids Confined Between an Oil Droplet and a Charged Solid Surface"
2023-09-07 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/1718/

Jan Rozman, "Extensile-Contractile Phase Separation in an Active Nematic Vertex Model"
2023-09-14 14:00 - 15:30 | MPS lecture hall (IJS)
The importance of nematic order and active nematic behaviour to epithelial morphogenesis is becoming increasingly clear. Several approaches have been developed to adapt vertex models, one of the most ubiquitous methods of modelling epithelia, to also include nematic activity. Here, we use one of these modified vertex models to study the dynamics of a mixture of extensile and contractile cells. We find that the two cell population separate over time, with the degree of separation depending on the magnitudes of extensile and contractile activity. This phase separation appears to be driven by two mechanisms. Firstly, only extensile model cells are intrinsically motile on their own. Therefore, the two populations move at different speeds when mixed. Secondly, contractile activity in the vertex model leads to cells of that type ‘sticking’ together, preventing separation.
https://indico.ijs.si/event/1753/

"Importance of variation in cytoplasm viscoelasticity throughout embryonic cell division"
2023-10-05 14:00 - 15:30 | Seminar room of physics (106) (IJS)
Speakers: Urša Uršič (Max Planck Institute of Molecular Cell Biology and Genetics)
The first few cell divisions are crucial for successful embryonic development of multicellular organisms. In order to divide properly, a myriad of biochemical and mechanical events need to be precisely coordinated. Mechanical events, such as positioning of the mitotic spindle, segregation of chromosomes, and cytokinesis, depend on the material properties of the cytoplasm. For more than a century, studies have consistently shown that the cytoplasm behaves as a viscoelastic material, with properties changing throughout the cell cycle stages. Nonetheless, variation of viscoelasticity throughout the cell cycle and its importance for correct embryonic cell division remains poorly understood.We aim to understand how different cytoplasmic components contribute to the viscoelastic properties through different stages of the cell cycle, focusing on the centrosome positioning mechanisms. We approach this question by using textit{Xenopus Laevis} cytoplasmic extract, which recapitulates several mechanical and biochemical processes of embryonic cell divisions. Cytoplasmic extracts are valuable model systems because they combine the complexity of textit{in vivo} systems with a wide possibility to be biochemically and mechanically modified. Using magnetic tweezers and introducing magnetic particles into the cytoplasmic extract, we probe the mechanical properties of the bulk cytoplasm. This reveals drastic increases in the fluidity of the cytoplasm during mitosis.To examine the mechanics of centrosome positioning, we encapsulate cytoplasmic extract with artificial centrosomes in oil. Interestingly, the dynamics of microtubules cause centrosomes to oscillate around the geometric center of the droplet, reaching the center of the droplet consistently at a very precise cell cycle stage of the extract. Linking centrosome positioning and variability of viscoelastic properties of the cytoplasm might offer insight into the mechanics of cell division in large embryonic cells, a subject that continues to be debated. In the future, understanding the mechanical properties of cytoplasm in early embryonic cells could reveal a better understanding of human embryonic development, potentially addressing the challenge of textit{in vitro} fertilization failure.
https://indico.ijs.si/event/1754/

Domen Vaupotič, "Effects of Coarse Graining on Topological Indices of Trees"
2023-10-26 14:00 - 15:00 | C/2-X – F1 čajnica (Jamova)
https://indico.ijs.si/event/1806/

Biophysics Journal Club: Marin Šako, "Industrial applications of cavitation"
2023-11-09 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/1807/

Anže Božič, "Towards improved simple models of electrostatic interactions in patchy colloids and proteins"
2023-11-16 14:00 - 15:00 | C/2-X – F1 čajnica (Jamova)
https://indico.ijs.si/event/1832/

Matej Kanduč, "The enigmatic boundary between hydrophilic and hydrophobic"
2023-11-23 14:15 - 15:15 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
Hydrophobic attraction, macromolecule adhesion, and even biofouling occur when the surface contact angle exceeds 65°, known as the “Berg limit.” While this threshold seems widely applicable, the reasons behind its universality remain unclear. In the seminar, I will discuss our current knowledge of this threshold and explore possible underlying mechanisms.
https://indico.ijs.si/event/1833/
