Department of Theoretical Physics

Jose Espinosa: Surprises in Vacuum Decay
2025-09-30 15:00 - 16:00 (Europe/Ljubljana) | C/2-X – F1 čajnica
In the standard lore the decay of the false vacuum of a single-field potential is described by a semi-classical Euclidean bounce configuration that can be found using overshoot/undershoot algorithms, and whose action suppresses exponentially the decay rate. While this is generically correct, the vacuum decay structure can be far richer. In some cases there is no bounce and decay proceeds via the so-called pseudo-bounces. In the general case with bounce, there are 2n+1 bounces, with n ranging from 0 (the standard case) to ∞. Some of these decays occur via “antibounces” which have the wrong behavior for overshoot/undershoot algorithms, that can miss them. Bounce and antibounce configurations form n pairs connected by pseudo-bounces.
https://indico.ijs.si/event/3088/

Santiago Tanco: Bayesian tools for the LHC: a proof of concept in di-Higgs searches
2025-10-02 11:00 - 12:00 | A/1-106 – Seminarska soba fizike (F5)
Extracting reliable physical information from collider data requires a combination of mathematical, computational and statistical tools to model observed distributions, often with the help of powerful simulations. But when simulations cannot be fully trusted, data-driven approaches become indispensable. In this talk, I will present Bayesian tools that provide a flexible, data-driven method for unsupervised training on probabilistic models of collider observables, highlighting their advantages for parameter inference and uncertainty estimation. I will illustrate these points in the context of pp > hh > bbbb searches, where recent analyses use a variation of the widely used data-driven “ABCD method”. Within our framework, the ABCD method can be generalized and improved, especially when its assumptions are not exactly satisfied, leading to more robust background subtraction. Our approach is able to exploit correlations in multi-dimensional data by modelling kinematic variables and b-tagging scores at the event level. These results also show a way in which simulations can be used as guides for unsupervised estimation of the true data distributions. Based on 2402.08001 and ongoing research.
https://indico.ijs.si/event/3054/

Bhabani Tripathy: doubly heavy tetraquarks
2025-10-06 15:00 - 16:00 | F1 tea room
Doubly heavy tetraquarks
https://indico.ijs.si/event/3101/

Aminul Islam Chowdhury: QCD medium in strong magnetic fields
2025-10-09 11:00 - 12:00 | F1 tea room
QCD medium in strong magnetic fields
https://indico.ijs.si/event/3103/

Franci Merzel, "Why are atomistic simulations (still) fascinating?"
2025-10-09 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
In this lecture, I will touch upon the development of methods and examples of the use of simulations in studying basic phenomena such as hydration of biomolecules, ligand binding, mechanisms related to biological function. We will also focus on the role of simulations in the interpretation of experimental data, especially in connection with neutron scattering, vibrational and NMR spectroscopy and cryo-electron microscopy. We will also talk about methodological solutions for overcoming size and time scales in MD simulations and about the importance of atomistic simulations in the age of AI.
https://indico.ijs.si/event/3052/

Manuel Morales: Parton distribution perspectives: future facilities and interplay with new physics
2025-10-16 11:00 - 12:00 | A/1-106 – Seminarska soba fizike (F5)
The precise determination of parton distribution functions (PDFs) is essential for accurate predictions of observables at hadron colliders. In this seminar, we will explore two complementary aspects of the future of PDF studies. The first concerns the potential of upcoming experimental facilities (e.g. a muon collider) to provide new constraints on PDFs and other parameters of interest. The second focuses on their interplay with signals of new physics: since PDFs are generally extracted under Standard Model (SM) assumptions, inconsistencies may arise when they are used to interpret or predict beyond the SM (BSM) phenomena. In this seminar, we will introduce and discuss key aspects of this PDF–BSM interplay and its broader implications for collider phenomenology.
https://indico.ijs.si/event/3076/

Tanmoy Sarkar (TBA)
2025-10-16 14:00 - 15:30 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/3099/

Benjamin Fuks: Seeking a coherent explanation of LHC excesses for compressed spectra
2025-10-23 11:00 - 12:00 | A/1-106 – Seminarska soba fizike (F5)
The most recent searches by the LHC collaborations in final states with soft leptons and missing transverse energy show mild excesses which can result from decays of electroweakinos featuring a compressed spectrum. We demonstrate that while recent searches in the monojet channel can exclude some of the associated parameter space regions, they exhibit overlapping excesses in certain models, including a simplified scenario with pure higgsinos. We further explore an array of models that go beyond the simplified scenarios considered by the experimental collaborations, and show that the excesses persist in realistic supersymmetric models featuring a bino-like lightest supersymmetric particle with some wino admixture. On the other hand, for the Next-to-Minimal Supersymmetric Standard Model with a singlino-like lightest supersymmetric particle and higgsino-like next-to-lightest supersymmetric particles, the excess in the two-lepton channel fits rather well with the parameter space predicting the correct relic abundance through freeze out, but the monojet fit is much poorer. Interestingly, the excesses either do not overlap or do not exist at all for two non-supersymmetric models seemingly capable of producing the correct final states.
https://indico.ijs.si/event/3029/

Toshikaze Chiba, "Junctional Fluctuations in 3D Epithelial Tissue"
2025-10-23 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/3100/

Michele Tammaro: Transport equation for Ultra-High Energy neutrino events
2025-11-06 11:00 - 12:00 | F1 tea room
We develop a first-principles formalism, based on the transport equation in the line-of-sight approximation, to link the expected number of muons at neutrino telescopes to the flux of neutrinos at the Earth’s surface. We compute the distribution of muons inside Earth, arising from the up-scattering of neutrinos close to the detector, as well as from the decay of taus produced farther away. This framework allows a fast semi-analytical calculation of the expected number of events, accounting for systematic uncertainties, as well as clarifying the assumptions behind definitions commonly used in the literature. As a working case, we apply this formalism to analyze the high-energy muon event recorded by KM3NeT, with a reconstructed energy of approximately 120 PeV, in comparison with the non-observation of similar events by IceCube. We derive the tension between the two experiments under different assumptions for the neutrino flux, correcting previous results found in literature. Finally, the formalism can be easily extended to include other type of events, furthermore allowing one to treat potential beyond-the-Standard-Model sources of muons.
https://indico.ijs.si/event/3286/

Lovro Lotrič, "Effect of curvature on surface tension"
2025-11-06 14:00 - 15:00 | C/2-X – F1 čajnica (Jamova)
https://indico.ijs.si/event/3104/

Vid Pograjc, "Computational Chemistry of L-DOPA, Phenol/Catechol, and Ammonia: My Past Research"
2025-11-13 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/3105/

Primož Ziherl (TBA)
2025-11-20 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/3106/

Ilia Musco: New perspectives on primordial black holes
2025-11-25 11:00 - 12:00 | Room 2.04 (FMF, Math building)
The possibility of primordial black holes (PBHs) forming in the early Universe from the collapse of cosmological perturbations has received lots of attention in the last ten years after the first detection of gravitational waves. PBHs span a very wade range of masses, from the particle size, interesting as dark mater candidate, to the solar mass range contributing to LVK signals, to the seeds of supermassive black holes, explaining the formation of high redshift AGN. In this talk I will explain the mechanism of PBH formation using numerical simulations starting from cosmological initial conditions, discussing the possible cosmological impact, and the open issues related to non linear aspects of the problem.
https://indico.ijs.si/event/3334/

Patrick Stengel: Nuclear recoil detection with color centers in bulk lithium fluoride
2025-11-27 11:00 - 12:00 | A/1-106 – Seminarska soba fizike (F5)
We present initial results on nuclear recoil detection based on the fluorescence of color centers created by nuclear recoils in lithium fluoride. We use gamma rays, fast and thermal neutrons, and study the difference in responses they induce, showing that this type of detector is rather insensitive to gamma rays. We use light-sheet fluorescence microscopy to image nuclear recoil tracks from fast and thermal neutron interactions deep inside a cubic-centimeter sized crystal and demonstrate automated feature extraction in three dimensions using machine learning tools. The number, size, and topology of the events agree with expectations based on simulations with TRIM. These results constitute the first step towards 10-1000g scale detectors with single-event sensitivity for applications such as the detection of dark matter particles, reactor neutrinos, and neutrons.
https://indico.ijs.si/event/3293/

Miroslav Vořechovský, "Model for Mechanistic Coupling of Patterning and Proliferation in Organoids by a 3D Vertex Model"
2025-11-27 14:15 - 15:15 | Seminar room of physics (106) (IJS)
A three-dimensional computational model inspired by the work Okuda and his collaborators , is developed to reveal the interaction between patterning and proliferation in epithelial tissue. The geometrical representation is based on Voronoi cells representing individual cells and differentiating the lateral, apical an basal cell faces. The viscous-damped system of forces controlling the shape of the multicellular tissue is derived from a potential featuring both volumetric and surface terms. Equipped with the cell rearrangements via cell-neighbor exchanges, the model allows for cell division and splitting while following the cell cycles.Fig. 1 Cell division during pattern-driven growth from initial single-layered spherical organoid.Pattering is controlled by the interplay of two morphogens (activator and inhibitor) in a reaction-diffusion system . The formation of patterns controls the cell proliferation in which the local concentration of activator which plays a role of a mitogen. The cell growth rate is modelled via Hill equation in which the exponent plays a central role in the presented coupling between patterning and proliferation.The developed model is used to decipher the diverse roles of ERK and Akt signaling in organoid morphogenesis by matching the laboratory data. In our computational model of multicellular organoid growth, we have identified a feedback loop between the formation of patterns, influencing the rate of cell proliferation and consequently the tissue mass increase. This feedback loop critically impacts the subsequent patterning through a diffusive-reaction system of morphogens. The interplay between proliferation and patterning accurately captures experimentally observed variations in the shapes of growing mammary gland organoids in the presence of two types of FGF: WT and Stab. The integration of the model with laboratory data and its biological interpretation are presented in a complementary contribution.REFERENCES Okuda, S., Inoue, Y. & Adachi, T. Three-dimensional vertex model for simulating multicellular morphogenesis. Biophysics and Physicobiology 12, (2015) 13–20. doi:10.2142/biophysico.12.0_13 Gierer, A. & Meinhardt, H. A theory of biological pattern formation. Kybernetik 12, (1972) 30–39. doi:10.1007/bf00289234Acknowledgement: Czech Science Foundation project no. GA23-04974S.
https://indico.ijs.si/event/3289/

Jan Rozman, "Multi-Phase Field Tissue Modelling: Fluidisation, Internal Dissipation, and Hole Formation"
2025-12-04 14:00 - 15:00 | C/2-X – F1 čajnica (Jamova)
https://indico.ijs.si/event/3288/

Anders Eller Thomsen: Functional EFT Methods: New Developments and the Matchete Tool
2025-12-11 11:00 - 12:00 | A/1-106 – Seminarska soba fizike (F5)
With the absence of new resonance discoveries at the LHC, the role of Effective Field Theories (EFTs) in Beyond the Standard Model (BSM) physics has become increasingly crucial. EFTs serve as indispensable tools in precision physics, offering the potential to reveal indirect evidence of new phenomena. Matching calculations can bridge the gap between underlying theories and EFTs and should ideally be performed at the loop level to include all relevant effects. In this talk, I will discuss functional methods as an avenue to perform cutting-edge matching and RG calculations. From a practical perspective these methods form the foundation of the public automated matching tool Matchete, and I will outline some of its core functionality.
https://indico.ijs.si/event/3080/

Kristjan Muursepp: Baryogenesis from bubble collisions
2025-12-12 11:00 - 12:00 | F1 tea room
In this talk I will consider models connecting baryogenesis with first order phase transition. In particular, I will elaborate on scenarios where the required amount of CP-violation originates from the production of heavy particles after scalar shells interpolating between true and false vacuum collide. I will focus on the case when both heavy particles are produced on-shell as well as the opposite regime when one of the heavy particles is produced off-shell, subsequently decaying to light Standard Model states. I will elaborate on the phenomenological implications of both scenarios.
https://indico.ijs.si/event/3291/

Dominik Haslehner: Running Field-Space Curvature from Quantum Corrections
2025-12-18 10:45 - 11:45 | F1 tea room
We present a systematic study of one-loop quantum corrections in scalar effective field theories from a geometric viewpoint, emphasizing the role of field-space curvature and its renormalisation. By treating the scalar fields as coordinates on a Riemannian manifold, we exploit field redefinition invariance to maintain manifest coordinate independence of physical observables. Focusing on the non-linear sigma model (NLSM) and (phi^4) theory, we demonstrate how loop corrections induce momentum- and scale-dependent shifts in the curvature of the field-space manifold. These corrections can be elegantly captured through the recently proposed geometry-kinematics duality, which generalizes the colour-kinematics duality in gauge theories to curved field-space backgrounds. Our results highlight a universal structure emerging in the contractions of Riemann tensors that contribute to renormalisation of the field-space curvature. In particular, we find explicit expressions and a universal structure for the running curvature and Ricci scalar in simple models, illustrating how quantum effects reshape the underlying geometry. This geometric formulation unifies a broad class of scalar EFTs, providing insight into the interplay of curvature, scattering amplitudes, and renormalisation.
https://indico.ijs.si/event/3439/

Anže Božič, "Some electrostatics of proteins and capsids"
2026-01-15 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/3107/

Sofie Martins: Computing cross-sections from the lattice — A recent shift in lattice thinking paradigms?
2026-01-22 11:00 - 12:00 | A/1-106 – Seminarska soba fizike (F5)
Extracting scattering amplitudes — and consequently cross-sections — from non-perturbative lattice techniques has seen significant advances in recent years. People have so far relied on Luescher’s method, which relates Euclidean finite-volume effects of lattice correlators to infinite-volume Minkowskian Scattering Amplitudes. While this method has achieved enormous success, its limitations are somewhat discouraging: the invalidity beyond the inelastic threshold limits predictions to lower-point exclusive particle-scattering processes. New lattice methods by Hansen/Bulava and Tantalo/Patella have addressed this by rethinking the computation of scattering amplitudes on the lattice in terms of spectral densities, which we can extract from large lattices with increasing precision. These methods allow the examination of exclusive processes even above the inelastic threshold and are consequently an invaluable tool for comparing and complementing perturbative computations with lattice results.I will present preliminary results for the Hansen/Bulava method in a particularly tractable theory that models a gauge-invariant implementation of the electroweak sector.
https://indico.ijs.si/event/3407/

Leah Rank, "Hollow microgels: From single particle characterisation to bulk behaviour"
2026-01-22 13:00 - 14:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
Hollow microgels are elastic polymer shells easily realisable in experiments. Recent works have shown the emergence of buckling events in dilute hollow microgels under the effect of an added osmotic pressure. Here, we perform large-scale simulations to show that these microgels at high enough packing fractions undergo spontaneous symmetry-breaking deformations ranging from single large dents to multiple indentations, even in the absence of any externally applied stress. This self-induced buckling phenomenon is thus solely driven by interparticle crowding. We construct a phase diagram inspired by vesicle shape theories, mapping local curvature metrics as a function of the reduced volume, to quantify these findings, and we also propose ways to observe the occurrence of buckling in experiments. The present results thus rationalize the deformations occurring in suspensions of micro- and nano-scale elastic shells, offering a synthetic analogue to biological ones and allowing direct control on buckling instabilities for potential applications. Beyond materials design, these insights may also help to describe shape regulation in natural systems such as cells and vesicles, where similar deformations are observed.
https://indico.ijs.si/event/3442/

Urban Bren, "Biomolecular Simulations as a Useful Tool in a Fight against Cancer"
2026-01-29 14:15 - 15:15 | Seminar room of physics (106) (IJS)
The lecture focuses on food safety in the context of chemical carcinogens, which are often present in raw or thermally processed foods and, after initial activation, alkylate DNA, usually guanine at position N7. Recently, important biochemical phenomena have been discovered, such as DNA catalysis of genetic damage, biomolecular cooperativity, in-vivo persistence of DNA adducts and the mutational propensity of DNA polymerases, which still lack an adequate mechanistic explanation. To elucidate their molecular basis, we used a range of state-of-the-art computer simulation techniques in conjunction with free energy calculations and the corresponding thermodynamic cycles. Since microwaves have been shown to catalyze numerous chemical reactions, we are concerned about the possibility of increased reactivity of chemical carcinogens, which also offers an explanation for why microwaves were recently classified as potentially carcinogenic by the World Health Organization. Therefore, we considered the reactions between chemical carcinogens and DNA in the context of our recently proposed physical mechanism of microwave catalysis, based on rotationally excited polar reaction species. Moreover, microwave irradiation has been shown to accelerate peptide misfolding and aggregation, processes that are generally associated with the occurrence of certain cancer types, e.g. amyloidosis. The microwave-irradiated solution thus through rotationally excited water molecules presents a less polar and less protic medium, thereby accelerating the harmful misfolding of peptides and their aggregation. We tested this hypothesis using molecular dynamics simulations in combination with a dedicated integrator, which is capable of efficiently decoupling individual degrees of freedom of water molecules and connecting them with the corresponding thermostats. Furthermore, we have used quantum chemical approaches to study the reactions between chemical carcinogens and polyphenols, secondary metabolites from fruits and vegetables. As a general rule for preventing DNA damage, a chemical carcinogen should react faster with a polyphenol scavenger than with DNA. Since the activation free energy represents a direct measure of reactivity, the reaction of a chemical carcinogen with a scavenger should have a lower activation barrier than the competitive alkylation of DNA. The long-term goal is to discover natural compounds or their mixtures with high antigenotoxic activities that could, after optimization, serve as functional dietary supplements and thus significantly contribute to cancer prevention.
https://indico.ijs.si/event/3605/

Aleks Smolkovič - Fast and differentiable EFT likelihoods
2026-01-30 10:30 - 11:30 | F1 tea room
The Standard Model Effective Field Theory (SMEFT) has proven to be a valuable framework for studying a broad class of models beyond the SM containing heavy degrees of freedom. The phenomenology of SMEFT can be developed systematically, incorporating essential effects such as Renormalization Group evolution and matching onto subsequent low-energy Weak Effective Field Theories (WET), enabling predictions for a wide range of observables. A likelihood function for the SMEFT that compares theory predictions to experimental data can be employed to identify patterns of deviation from SM predictions, but also to study the phenomenology of any specific model that can be matched onto SMEFT. In this talk, we present a new open source Python package jelli – JAX-based EFT likelihoods, which provides fast and analytically differentiable generic likelihood functions for EFT studies. We discuss a major new version of smelli – a SMEFT likelihood, which incorporates a large number of observables, ranging from quark and lepton flavor physics, to Higgs physics, electroweak precision observables, beta decays, and high-mass Drell-Yan tails. Running on the jelli backend, it provides a global flavorful likelihood function for the SMEFT, WET, and for new physics models, with no assumptions on the flavor structure. Thanks to its numerical efficiency and differentiability, it opens up new avenues in exploring BSM parameter spaces.
https://indico.ijs.si/event/3638/

Stephane Jedele, "Enhancement of the RNA tree model"
2026-02-05 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/3599/

Toshikaze Chiba, "Deep Learning and Large Language Models for scRNA-seq Data Analysis"
2026-02-12 14:00 - 15:00 | MPŠ Lecture Hall (Jamova)
https://indico.ijs.si/event/3637/

Fabrizio Nesti: A ghost story
2026-03-05 11:00 - 12:00 | F1 tea room
https://indico.ijs.si/event/3697/

Fabian Esser: Higher-dimensional SMEFT operators and UV models for neutrinoless double beta decay
2026-03-12 11:00 - 12:00 | A/1-106 – Seminarska soba fizike (F5)
The observation of lepton number violation (LNV) would be clear evidence for physics beyond the Standard Model, and non-zero neutrino masses particularly motivate a study of processes that violate lepton number by two units, like e.g. neutrinoless double beta decay. In the Standard Model Effective Field Theory (SMEFT), a ubiquitous framework used for indirect new physics searches, $Delta L =2$ operators appear at dimension-5 and higher odd dimensions. Focusing on dimension-9 operators, I will present a diagram-based classification of tree-level UV models and isolate minimal two-particle models that avoid generating the dimension-5 operator or dimension-7 LNV operators at tree level. I then chart how these minimal models populate the operator landscape and organise them by the loop order at which they radiatively induce lower-dimensional LNV operators, highlighting sce- narios in which the tree-level dimension-9 contribution can compete with or dominate loop-suppressed neutrino-mass (dimension-5) effects. Finally, I will show representative one-loop and two- loop models, their matching onto the SMEFT, and their implications for neutrino masses, charged-lepton flavour violation, and the relative size of dimension-9 versus dimension-5 contributions to 0νββ.
https://indico.ijs.si/event/3692/

Ana Crnković, "Engineering protein nanopores with genetically encoded noncanonical amino acids"
2026-03-26 14:15 - 15:15 | Seminar room of physics (106) (IJS)
Genetic code expansion enables site-specific incorporation of noncanonical amino acids (ncAAs) into proteins, facilitating the introduction of spectroscopic probes, fluorescent labels, photoreactive groups, enhanced stability, and novel chemical reactivity. Despite the successful incorporation of over 150 ncAAs, the broader application of ncAAs has largely remained limited to proof-of-principle studies. In this lecture, I will discuss key factors that govern the efficient incorporation of ncAAs to achieve high yields of target proteins, with particular emphasis on challenging systems such as phosphoproteins and selenoproteins. In the second part, I will highlight how selected ncAAs are utilized in our group to engineer protein nanopores for biosensing applications – a technique that detects analytes by monitoring changes in ionic current as molecules translocate through a nanopore under an applied voltage. Overall, this lecture aims to highlight the potential of ncAAs to unlock new functionalities in various protein targets and to inspire their broader use in emerging techniques.
https://indico.ijs.si/event/3701/
