Department of Theoretical Physics

Martin Schmaltz: Hubble tension update
2025-07-03 11:00 - 12:00 (Europe/Ljubljana) | https://www.youtube.com/@astroFMF/streams (F4 – FMF)
This seminar will give an introduction to and status update of the Hubble tension, the 6 sigma discrepancy between the two most precise methods for measuring the expansion rate of our Universe. The most promising resolutions of the tension employ “early” new physics to modify the sound horizon, the standard ruler used in CMB and BAO based determinations of the expansion rate. A possibly related new piece of the puzzle might be the recent evidence for non-standard dark energy from the DESI experiment.
https://indico.ijs.si/event/3014/

Raquel Molina: Quark mass dependence of hadron resonances
2025-07-07 11:00 - 12:00 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
https://indico.ijs.si/event/2976/

David Kaplan: Shadow Matter
2025-07-10 11:00 - 12:00 | https://www.youtube.com/@astroFMF/streams (F2 – FMF)
I will review how one gets classical physics from quantum theories. Then I will show that there are quantum states of the field theories of general relativity and electromagnetism that we typically ignore, but have interesting phenomenological effects. These states amount to loosening the constraint equations in GR and EM. Doing so in GR sources non-dynamical parts of the metric which mimic a pressureless dust, with some odd features, and thus these effects may be the explanation as to why we think there is dark matter. The constraint in EM is Gauss’ Law, and turning it off mimics a charge density that does not respond to electric forces, but follows geodesics. I will briefly discuss the cosmological consequences of these new fields and potential studies.
https://indico.ijs.si/event/3015/

Fabio Staniscia (TBA)
2025-07-10 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/3006/

Lorenzo Ubaldi: Schwinger current in de Sitter
2025-07-25 16:00 - 17:00 | https://zoom.us/j/94950883072 (F1 – tea room)
We study classical background electric fields and the Schwinger effect in de Sitter space. We show that having a constant electric field in de Sitter requires the photon to have a tachyonic mass proportional to the Hubble scale. This has physical implications for the induced Schwinger current which affect its IR behaviour. To study this we recompute the Schwinger current in de Sitter space for charged fermions and minimally coupled scalars imposing a physically consistent renormalization condition. We find a finite and positive Schwinger current even in the massless limit. This is in contrast to previous calculations in the literature which found a negative IR divergence. We also obtain the first result of the Schwinger current for a non-minimally coupled scalar, including for a conformally coupled scalar which we find has very similar behaviour to the fermion current. Our results may have physical implications for both magnetogenesis and inflationary dark matter production.
https://indico.ijs.si/event/3030/

Basudeb Dasgupta: Probing Dark Matter with Low-Mass Black Holes
2025-09-04 15:30 - 16:30 | A/1-106 – Seminarska soba fizike (F5)
Heavy non-annihilating dark matter captured by neutron stars can trigger collapse into low-mass black holes, producing subsolar-mass mergers detectable by gravitational wave observatories. These events probe dark matter-nucleon interactions at cross-sections below the neutrino floor and dark matter masses from GeV to PeV. Existing LIGO/Virgo data already place strong bounds; future detections could reveal dark core collapse and explain anomalies like the missing pulsars near the Galactic Center. I will discuss how to distinguish low-mass black holes from neutron stars via gravitational wave signatures, and how this affects sensitivity to dark matter.
https://indico.ijs.si/event/2816/

Katarina Kokalj, "Newton black films"
2025-09-11 14:00 - 15:00 | A/1-106 – Seminarska soba fizike (F5) (Jamova)
https://indico.ijs.si/event/3050/

Damir Bečirević: Why the radiative decays of quarkonia are important
2025-09-18 15:30 - 16:30 | A/1-106 – Seminarska soba fizike (F5)
TBA
https://indico.ijs.si/event/3046/

Ryan Plestid: Detecting dark matter with a picogram detector
2025-09-25 15:30 - 16:30 | A/1-106 – Seminarska soba fizike (F5)
Dark matter direct detection is dominated by a landscape of macroscopic detectors. How then can quantum sensors, such as an atom interferometer compete? In this talk I will outline recent work on how large coherent enhancements amplify dark matter signals in an atom interferometer. All of the necessary theory is elementary quantum mechanics, and yet the role of N-enhancements is subtle, due to the many-branched nature of an atom intereferometer’s wave function.

Based on: 2402.03421 and 2509.13417
https://indico.ijs.si/event/3028/

Jose Espinosa: Surprises in Vacuum Decay
2025-09-30 15:00 - 16:00 | 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/
