Department of Theoretical Physics

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

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/

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/

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/

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/

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/

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/

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

Martin Schmaltz: Hubble tension update
2025-07-03 11:00 - 12:00 | 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/
