Department of Theoretical Physics

Jan Rozman, "From Substrate Dissipation to Internal Dissipation Vertex Model Dynamics: Generating Sustained Flows"
2024-09-02 14:00 - 15:00 (Europe/Ljubljana) | C/2-X – F1 čajnica (Jamova)
Speakers: Jan Rozman
Complex tissue flows in epithelia are driven by intra- and inter-cellular processes that generate, maintain, and coordinate mechanical forces. There has been growing evidence that cell shape anisotropy, manifested as nematic order, plays an important role in this process. Here we extend an active nematic vertex model by replacing substrate friction with internal viscous dissipation, dominant in epithelia not supported by a substrate or the extracellular matrix, which are found in many early-stage embryos. When coupled to cell shape anisotropy, the internal viscous dissipation allows for long-range velocity correlations and thus enables the spontaneous emergence of flows with a large degree of spatiotemporal organisation. We demonstrate sustained flow in epithelial sheets confined to a channel, providing a link between the cell-level vertex model of tissue dynamics and continuum active nematics, whose behaviour in a channel is theoretically understood and experimentally realisable. Our findings also show a simple mechanism that could account for collective cell migration correlated over distances large compared to the cell size, as observed during morphogenesis.
https://indico.ijs.si/event/2245/

Nudžeim Selimović: Topological Portal to the Dark Sector
2024-08-29 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
I will discuss a novel topological portal between quantum chromodynamics (QCD) and a dark QCD-like sector. Such a portal is present only for a unique coset structure after QCD confinement and it connects three QCD to two dark pions. When gauged, it is the leading portal between the two sectors, providing an elegant self-consistent scenario of light thermal inelastic dark matter. The inherent antisymmetrization due to a Wess–Zumino–Witten-like effective interaction leads to diminished annihilations at later times and suppressed direct detection. However, novel collider signatures offer tremendous prospects for discovery at Belle II. The talk is based on https://arxiv.org/abs/2401.09528 with Joe Davighi and Admir Greljo.
https://indico.ijs.si/event/2247/

Luighi Leal: Correlating $0 ubetabeta$ decays and flavor observables in leptoquark models
2024-07-11 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
https://indico.ijs.si/event/2231/

Chandan Hati: Nonstandard Nucleon Decays
2024-06-28 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
Nucleon decays are generic predictions of many well motivated theories, including those based on the unification of forces and supersymmetry. I will discuss how nonstandard nucleon decays offer a unique opportunity to broadly probe light new particles beyond the Standard Model with masses below few GeV, including axion-like particles, dark photons, sterile neutrinos, and scalar dark matter. Conventional searches can misinterpret and even completely miss such new physics. I will discuss a general strategy based on momenta of visible decay final states to probe these processes, offering a rich physics program for existing and upcoming experiments such as Super-Kamiokande, Hyper-Kamiokande, DUNE, and JUNO.
https://indico.ijs.si/event/2173/

Manuel Szewc: Modeling Hadronization with Machine Learning
2024-06-27 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
A fundamental part of event generation, hadronization is currently simulated with the help of fine-tuned empirical models. Motivated by the difficulties of these models, in this talk I’ll present MLHAD: a proposed alternative where the empirical model is replaced by a surrogate Machine Learning-based model to be ultimately data-trainable. I’ll detail the current stage of development and discuss challenges and possible ways forward.
https://indico.ijs.si/event/2088/

Martín Novoa-Brunet: NP @ High Precision beta decay
2024-06-26 13:00 - 14:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
https://indico.ijs.si/event/2166/

Ezequiel Alvarez: The Information frontier at the LHC
2024-06-17 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
Once we have obtained the data, the question is how much information is encoded in it and how we can extract it. Any framework with this purpose utilizes information-besides-data and mathematical and statistical tools. Bayesian statistics has the virtue that, by modeling the inner structure of the data, it allows us to inject prior information and its uncertainty as a catalyst to push out the information from the data. The framework also possesses tools to assess the results unbiasedness and its consistency with the data. We will show with examples at the LHC how to apply Bayesian tools in order to efficiently extract information about the physics inside. We discuss possible applications in improving data-driven methods, and in pp > hh > bbbb, however the generality of the results apply to rethinking a variety of observables. The method can exploit correlations at the event-by-event level and previously untapped strengths such as for instance continuity and unimodality of some distributions. We raise the question of whether there might be room for improvements in some of the current LHC analyses.
https://indico.ijs.si/event/2135/

Tatyana Gavrilchenko, "Lessons from the tracheal terminal cell: what a unicellular network can teach us about distribution network design principles"
2024-06-13 14:15 - 15:15 | Seminar room of physics (106) (IJS)
Speakers: Tatyana Gavrilchenko (Flatiron Institute, NY, USA)
The insect respiratory system is a network of air-filled tubes permeating the animal body, supplying oxygen for metabolic activity and removing waste carbon dioxide. The majority of gas exchange occurs in the finest regions of the tracheal system, the terminal cells. These cells have a unique and highly specialized tree-like structure with long thin branches, reminiscent of neuronal arbors. While many aspects of the terminal cell are understood on a molecular level, including the mechanisms that guide branch extension and lumen formation, the macroscopic network features that allow for proper oxygen distribution remain mysterious. We use the Drosophila terminal cell as a model system for fundamental developmental problems of network structure and functions, utilizing an imaging data set that fully maps the structure of over one hundred individual cells. First, we find that scaling relations succinctly encapsulate the dynamics of growing networks, and use the empirical scalings observed in the terminal cells to construct a minimal model of network growth that describes the system. Second, to understand the interplay between structure and function in the trees, we developed a model of oxygen distribution by a network embedded in a two-dimensional absorbing tissue, driven purely by diffusion along oxygen partial pressure gradients. Our method works well on complex geometries, including curved and branched networks that approximate the geometry of the terminal cells. These investigations offer insights into mammalian capillary networks, which have different structural features and delivery mechanisms from terminal cells but are guided by similar developmental principles. Understanding the salient features that govern the structure of these biological networks is essential to designing synthetic vasculature, a major step in the manufacture of artificial organs.
https://indico.ijs.si/event/2138/

Bernat Corominas-Murtra, "Topological transitions and cell-cell adhesion properties in development"
2024-06-10 12:00 - 13:00 | Seminar room of physics (106) (IJS)
Speakers: Bernat Corominas-Murtra (Karl-Franzens University Graz)
The developmental process implies precise but significant changes in the geometry and structure of the embryonic tissues. Recent results show that apparently minor changes in adhesion at the local level of cell-cell contacts trigger deep, non-linear transitions in the topological organization of the whole embryonic tissue and, in consequence, change its material properties and facilitate geometrical deformations. Open questions remain, like the potential existence of causal feedbacks between cell differentiation processes and the potential heterogeneity of topological patterns existing within the tissue. The results presented in this talk are based on the fundamental assumption that predictive frameworks in theoretical biology must explore the connection between different scales of the system. In this particular case, we use topology to establish a bridge between the system’s scales defined by i) the cell level and ii) the tissue level. This enables us to predict global, non-trivial behaviours in tissues from the empirically feasible observables related to the mechanical properties of single cells.
https://indico.ijs.si/event/2139/

Mario Reig Lopez: Testing the far UV of the Standard Model with axions
2024-05-30 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
In this talk I will discuss axion couplings to gauge bosons in 4-dimensional Grand Unified Theories and in (heterotic) String Theory. The topological nature of these couplings allows them to be matched from the UV to the IR, and the ratio of the anomaly with photons and gluons for any axion is fixed by unification. I will show that this implies that there is a single axion — the QCD axion — with an anomalous coupling to photons. Other light axion-like particles can couple to photons by mixing with the QCD axion, and necessarily lie to the right of the QCD line prediction in the mass-coupling plane. As a result, a discovery of an axion to the left of the QCD line can rule out simple GUTs and some heterotic string compactifications.Based on: 2206.07053 and future work.
https://indico.ijs.si/event/2085/

Innes Bigaran: Leveraging intermediate resonances to probe CP-violation at colliders
2024-05-28 13:45 - 14:45 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
We study the phenomenological implications of interference between tree-level contributions to decays to three-body final states. CP-violation in these decays arise via different virtualities of intermediate resonances, and the presence of SM and/or new CP phases in a model Lagrangian. We highlight the manifestation of this CP-violating observable in the interference between SM charged-current decays and new-physics contributions to effective vector interactions in the EFT and in a UV-complete model featuring a scalar leptoquark, $S_1$. We present a novel method for searching for CP-violating new physics effects utilising the differential cross sections of $ppto d_i ell u_ell$ decays, with a detailed study of $ppto b tau u_tau$ simulating signal and background.
https://indico.ijs.si/event/2146/

Gašper Lipnik, "Force inference in epithelial tissues"
2024-05-23 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
In this work, we explore the ways of determining the mechanical properties of epithelial tissues. Knowledge of the mechanical parameters like forces between and pressures within cells leads to a deeper understanding of the processes in these tissues. To determine these parameters, one can perform in vivo measurements using lasers, optical tweezers, micropipettes etc. However, in vivo measurements are invasive, technically challenging and local. Thus, it is best to use noninvasive and global methods. One theoretical approach is force inference from cell shapes and connectivity as seen in microscope images, and here we introduce three force inference methods.
https://indico.ijs.si/event/2091/

Nudžeim Selimović
2024-05-23 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
https://indico.ijs.si/event/2089/

Diego Redigolo: Dark sectors at flavor factories
2024-05-21 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
I will discuss new ideas for reporpusing current flavor experiments to hunt for dark sectors particles.
https://indico.ijs.si/event/2134/

Lorenzo Ubaldi: False Vacuum Decay From Thin to Thick Walls
2024-05-16 14:00 - 15:00 | https://uu-se.zoom.us/j/64706033081 Passcode: [REDACTED] (Zoom)
The computation of the false vacuum decay rate in the situation with nearly degenerate vacua can be performed analytically in the well known thin wall approximation. If we depart from the near degeneracy of the vacua, the approximation quickly ceases to work. This statement is known to practitioners of the field, but it has a caveat: it is true only if one works at the leading order of the thin wall approximation. In this talk I will describe how to organize the calculation to systematically include higher order corrections in the thin wall parameter expansion. The first few orders can be computed analytically. It is enough to include them to improve the approximation and get a very accurate estimate of the bounce action also deep into thick wall regimes, where the vacua are far apart. I plan to also briefly discuss how to deal in these cases with the calculation of the functional determinant, also known as the prefactor, in order to have the full proper understanding of the vacuum decay rate. In the whole talk I will only consider flat spacetime, without gravity.
https://indico.ijs.si/event/2133/

Maciej Kierkla: EFT of supercooled phase transition
2024-05-09 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
We present an analysis of the first-order supercooled phase transition associated with symmetry breaking in the early Universe in a classically scale-invariant model. We analyze the role of higher order thermal corrections for these transitions, and to what extent they can be computed using dimensionally reduced effective field theory (3D EFT). This framework requires high temperature (HT) expansion to be valid, which seems challenging due to the presence of supercooling. We show how to reliably use the HT expansion in dimensionally reduced theory for the calculation of bubble nucleation rate. We compare the obtained results to the results of the most common scheme based on the so-called daisy resummation. We further compute all of phase transition characteristics, discuss various scenarios of completing the transition and predict resulting gravitational-wave spectra and their observational prospects in future experiments such as LISA.
https://indico.ijs.si/event/2070/

Labrini Athanasopoulou (TBA)
2024-04-18 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2076/

Boštjan Vihar, "Developing in vitro models of human tissues"
2024-04-11 14:15 - 15:15 | Seminar room of physics (106) (IJS)
Speakers: Boštjan Vihar (IBV MF UM)
The presentation will establish basic concepts of tissue engineering, 3D biofabrication and the development of microphysiological systems, and provide insight into some of the work in progress at the Institute of Biomedical Sciences, Faculty of Medicine, University of Maribor (IBV).The development of advanced in vitro models of human tissues stands at the forefront of advancing medical sciences by developing innovative solutions to complex health issues and requires an interdisciplinary approach combining different fields such as cell and molecular biology, biochemistry, materials science, additive technologies. The development process can vary substantially depending on the target tissue/application and the expected functional characteristics.At IBV different aspects of in vitro tissue model development are explored in parallel and in synergy in the hopes of obtaining new insights into the (patho)physiology of human tissues and organs and creating new ways for the treatment of complex diseases and personalized medicine.Our research activities include the cell culture of immortalized and primary cell lines, which are also isolated and characterization in-house. In parallel, polymer-based hydrogel formulations are developed to mimic the physico-chemical properties of native tissues and are combined with cells to form bioinks. Using extrusion-based, microfluidics and lithographic 3D printing techniques, tissue scaffolds and custom-made microfluidic devices are developed and integrated into microphysiological systems (organ-on-a-chip devices) which allow prolonged maturation, continuous monitoring and functional analysis.
https://indico.ijs.si/event/1866/

Fabio Staniscia, "Line adsorption in sessile droplets"
2024-04-04 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/2075/

"Dynamics of Ribonucleoprotein Assembly in Time and Space"
2024-03-28 14:00 - 15:00 | Seminar room of physics (106) (IJS)
Speakers: Miha Modic (National Institute of Chemistry)
Successful embryo implantation induces rapid morphological progression from rosette to lumen and then to gastrulation, which is closely coordinated with cell fate transition. By integrating machine learning, metabolic RNA sequencing, iCLIP, and proteomics of the protein-RNA interactome with embryology, I will present a blueprint for understanding how multilayered molecular networks coordinate developmental transitions. I will highlight three studies that demonstrate how cross-regulatory molecular logic ensures the robustness of developmental signalling pathways to rewire ribonucleoprotein assembly to drive cell fate transitions (Modic et al., 2023), important for the onset of gastrulation (Modic et al., 2019) and embryonic morphogenesis (Modic & van Genderen et al, in resubmission; Modic et al., Biorxiv 2021).
https://indico.ijs.si/event/1799/

Marco Gorghetto: Early vs late string networks from a minimal QCD Axion
2024-03-19 14:00 - 15:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
We propose a new regime of minimal QCD axion dark matter that lies between the pre- and post-inflationary scenarios, such that the Peccei-Quinn (PQ) symmetry is restored only on sufficiently large spatial scales. This leads to a novel cosmological evolution, in which strings and domain walls re-enter the horizon and annihilate later than in the ordinary post-inflationary regime, possibly even after the QCD crossover. Such dynamics can occur if the PQ symmetry is restored by inflationary fluctuations, i.e. the Hubble parameter during inflation $H_I$ is larger than the PQ breaking scale $f_a$, but it is not thermally restored afterwards. Solving the Fokker-Planck equation, we estimate the number of inflationary e-folds required for the PQ symmetry to be, on average, restored. Moreover, we show that, in the large parts of parameter space where the radial mode is displaced from the minimum by de Sitter fluctuations, a string network forms due to the radial mode oscillating over the top of its potential after inflation. In both cases we identify order one ranges in $H_I/f_a$ and in the quartic coupling $lambda$ of the PQ potential that lead to the late-string dynamics. In this regime the cosmological dark matter abundance can be reproduced for axion decay constants as low as the astrophysical constraint 𝒪$(10^8)$ GeV, corresponding to axion masses up to $10^{-2}$ eV, and with miniclusters with masses as large as 𝒪(10) solar masses.
https://indico.ijs.si/event/1997/

Mojca Krajnc (TBA)
2024-03-14 14:00 - 15:30 | Seminar room of physics (106) (IJS)
Speakers: Mojca Krajnc (Biotechnical Faculty)
https://indico.ijs.si/event/1778/

Urška Andrenšek, "Thickness modulation in supported epithelial sheets"
2024-02-29 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
Surface patterns in epithelial tissues often arise due to effects of differential surface tension and elastic properties of supporting structures, such as basal membrane and bulk elastic substrate. While we cannot clearly distinguish between surface-tension and elastic contributions only from measurement of wave-length of surface patterns, thickness modulation of the tissue might give a better insight into the origins of specific pattern formation. Depending on magnitude of surface-tension and elastic energy contributions, the thickness modulation can change its amplitude and phase. I will present the theoretical predictions of effects that differential surface tension, basal membrane and elastic substrate have on surface-pattern formation and thickness modulation in mono-layered epithelial sheets.
https://indico.ijs.si/event/1875/

Veronika Bukina (TBA)
2024-02-22 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/1874/

"One, two, three, four: simple additions of nucleic acid strands for complex functional outcomes"
2024-02-15 14:15 - 15:15 | Seminar room of physics (106) (IJS)
Speakers: Maja Marušič (National Institute of Chemistry)
Nucleic acids display a range of structural variations beyond the basic helical shape and Watson-Crick hydrogen bond pairing. Some of these structural variations are nuanced, while others result in a vastly different spatial conformation. We will discuss the structural details of single-, double-, triple- and quadruple-stranded nucleic acids and how structural variation translates into functional diversity. What can in vitro biophysical methods reveal about the nucleic acid structure, how can we correlate findings from diverse methods, and when is this approach suitable and when not? Insights into these and related questions will be provided using adenine-rich DNA systems, AT/GC repeat regions, PNA-RNA complexes and 3′ untranslated regions of mRNA.
https://indico.ijs.si/event/1769/

Marin Šako, "Physics of bubble oscillations"
2024-02-07 14:00 - 15:00 | C/2-X – F1 čajnica (Jamova)
Bubbles in liquids, soft and squeezy objects made of gas and vapour, yet so strong as to destroy any material. At first glance bubbles in water might seem like trivial objects with simple physics describing them. However, upon further investigation one finds many interesting phenomena. In this talk I will present Rayleigh–Plesset equation, a mathematical framework for describing bubble oscillations, as well as an overview of some notable solutions.
https://indico.ijs.si/event/1844/

Fran Ivan Vrban, "Many-body effects in microgel suspensions"
2024-02-01 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
Even though there are clear indications of many-body interactions in the dense microgel suspensions, there is still no adequate general description of the phenomena. One possible avenue for exploration of many-body effects is the coarse-grained liquid-drop model, where the soft matter constituents are regarded as compressible drops with a well-defined surface. The interplay between particle’s bulk and surface energy plays the key role in the system characterization, along with the geometry constraints. In this seminar, the general overview of the many-body interactions in field will be presented, as well as the relevant techniques and results of the liquid-drop model.
https://indico.ijs.si/event/1956/

Jules Morand, "Emergent circulation patterns from anonymized mobility data: Clustering Italy in the time of Covid"
2024-01-25 14:00 - 15:00 | C/0-106 – Seminarska soba fizike (F5) (Jamova)
Speakers: Jules Morand (Department of Physics, University of Trento)
https://indico.ijs.si/event/1873/

"Studies of bees with smart sensors: at the crossroads of biology, physics, and AI"
2024-01-11 14:15 - 15:15 | Seminar room of physics (106) (IJS)
Speakers: Anton Gradišek (Jožef Stefan Institute)
Honeybees and bumblebees are social insects and are among the most important pollinators in their ecosystems. They are fascinating creatures and even if we think that we know them well, there is still much to discover about their lives. In the seminar, I will present an overview of the studies we carried out especially in the field of bumblebee research. We used several sensors, especially microphones and thermometers, to investigate the daily dynamics of the colony. At the end, I will outline the current project we are working on, we will be using smart sensors to monitor stress on honeybee colonies in the presence of external stressors.
https://indico.ijs.si/event/1770/

Biophysics Journal Club: Tanmoy Sarkar, "Inclusion of adaptive tension and strain in vertex model"
2023-12-21 14:00 - 15:00 | C/2-X – F1 čajnica (Jamova)
https://indico.ijs.si/event/1834/
