Department of Theoretical Physics

Ilja Doršner: Fully Testable Axion Dark Matter within a Minimal SU(5) Unification Model
2023-02-23 11:15 - 12:15 (Europe/Ljubljana) | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
I will present a minimal Grand Unified Theory model, based on an SU(5) gauge symmetry and a global U(1) Peccei-Quinn symmetry, that predicts the existence of an ultralight axion dark matter within a narrow mass range between 0.1 neV and 4.7 neV. This mass window is determined through an interplay between gauge coupling unification constraints, partial proton decay lifetime limits, and the need to reproduce the experimentally observed fermion mass spectrum. The entire parameter space of the proposed model will be probed through a synergy between several low-energy experiments that look for proton decay (Hyper-Kamiokande), axion dark matter through axion-photon coupling (ABRACADABRA and DMRadio-GUT) and nucleon electric dipole moments (CASPEr Electric).
https://indico.ijs.si/event/1541/

[DBS lunch seminar] Denis Kutnjak: "Environmental virology and virus ecology: from plant virus diversity to monitoring SARS-CoV-2 in wastewater"
2023-02-16 14:00 - 15:30 | Seminar room of physics (106)
Abstract
Viruses likely represent the most diverse part of the biosphere; nevertheless, a large part of their diversity is still unknown. Viromics approaches, based on high-throughput sequencing, enable the studies of virus diversity inside and outside of their hosts, in different environments, where some viruses can persist for long periods of time. In the past few years, we have addressed the diversity of viruses in crop and wild plants, invertebrates, and different water types. We discovered several previously unknown viruses, mostly in wild plants and in surface water samples. Using viromics, we have also discovered a diverse set of nucleic acids of viruses infecting plants in wastewater and demonstrated their infectivity even after wastewater treatment using classical virology approaches. During the SARS-CoV-2 pandemic, we have extended wastewater analyses to measurements of the concentrations and detection of variants of this virus in wastewater from different Slovenian wastewater treatment plants. This resulted in a very early establishment of such monitoring on a national scale, which now helps us to better understand the epidemiological trends of SARS-CoV-2. In this lecture, different cases of research from the fields of virus discovery, environmental virology, virus ecology, and wastewater epidemiology will be presented.

Event information
The seminar will take place at 14h in the seminar room of physics (106) in the main building of Jožef Stefan Institute. The seminar will start with a snack (pizza) and will be followed by an informal discussion.

Robert Harlander: TBA
2023-02-16 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
https://indico.ijs.si/event/1547/

[Biophysics seminar] Fabio Staniscia: "Heat release effect in domain relaxation of long-range interacting systems"
2023-02-02 14:00 - 15:00 | Seminar room of physics (106)
The meeting will take place in the seminar room of physics (106).

Oliver Gould: Effective field theory for cosmological phase transitions
2023-02-02 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
A cosmological first-order phase transition would have given rise to a stochastic gravitational wave background which may be observable today. Phase transitions are driven by thermal loop fluctuations, which modify background fields at leading order. This breaks the usual loop expansion and leads to large theoretical uncertainties in typical calculations, especially for gravitational wave predictions. I will give an overview of our present understanding of these uncertainties, and of the tools that have been developed to overcome them. Effective field theory has been at the forefront of this development, and I will outline how it solves a number of long-standing theoretical problems.

https://indico.ijs.si/event/1551/

[Biophysics seminar] Tanmoy Sarkar
2023-01-26 14:00 - 15:00 | Seminar room of physics (106)
I will present a new approach to studying epithelial mechanics, which is based on representing the tissue structure by a graph. As a proof of concept, I will study a tissue with random cell rearrangements and compare the results with an alternative approach, based on a Markov chain.

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

[DBS lunch seminar]: Marko Gosak, "Quantifying Calcium Activity Patterns in Normal and Diabetic Pancreatic Islets of Langerhans with Network Analyses"
2023-01-19 14:00 - 15:30 | Lecture hall of IPS (MPŠ)
Islets of Langerhans consist of a large functional syncytium of beta cells that produce pulses of insulin, a key component for controlling metabolic homeostasis. In response to stimulation, the islet cells display rather well-coordinated intercellular activity patterns, which was found crucial for ensuring normal secretory patterns. However, it is not clear how coordinated cellular rhythmicity emerges within the heterogeneous cellular collectives and how it is altered in diabetes. To address these questions, we combined multicellular calcium imaging in mouse pancreatic tissue slices as well as in isolated human islets with advanced network analyses. Describing the intercellular activity patterns by means of network language has not only revealed that intercellular networks in islets share many architectural similarities with several other real-life networks, such as small-worldness, heterogeneity, and modularity, but also leads to important new insights into the relationship between cellular metabolic activity and the orchestration of collective behaviour [1,2]. Importantly, analyses of islets from diabetic donors have revealed that the intercellular activity in these islets is characterized by a lower fraction of global calcium waves and more segregated network structures [3]. However, there was a rather large variability in responses in islets from donors with diabetes, with some exhibited striking pathophysiological changes, whilst others behaved rather normally. This great heterogeneity in susceptibility of different islets towards diabetogenic insults should be considered as an important aspect by conducting further research on the pancreatic islets.

Figure: Analysis of calcium activity in the pancreatic cells in the islets of Langerhans and the generation of functional intercellular networks.

[1] Gosak M, et al., Network science of biological systems at different scales: A review, Physics of Life Reviews 2018, 24.
[2] Stožer A, et al., From isles of Königsberg to islets of Langerhans: Examining the function of the endocrine pancreas through network science, Frontiers in Endocrinology 2022, 922640.
[3] Gosak M, et al., Ca2+ oscillations, waves, and networks in islets from human donors with and without type 2 diabetes, Diabetes 2022, 71.

The seminar will take place in the lecture hall of the International Postgraduate School (MPŠ, https://www.mps.si/en/o-nas/lokacija/) at the Jožef Stefan Institute. It will be followed by discussion and snacks.

Luka Leskovec: A lattice QCD study of B → π π l 𝜈
2023-01-19 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
$V_{ub}$ is the smallest and least known of all CKM matrix elements; it’s currently determined primarily through the exclusive process B → π l 𝜈. I will present progress toward a lattice QCD determination of the $V_{ub}$​ matrix element from a novel transition — the B → π π l 𝜈 process, where the π π system is in a P-wave and features the ρ(770) resonance as an enhancement. The calculation is performed an ensemble with $N_f​=2+1$ isotropic clover fermions wiht $L≈3.6$ fm and a pion mass of 320 MeV; for the b-quark we use the anisotropic clover action. After a brief overview of the theoretical framework, I will discuss some preliminary results.
https://indico.ijs.si/event/1548/

[Biophysics journal club] Urška Andrenšek: "Muscular hydraulics drive larva-polyp morphogenesis"
2023-01-12 14:00 - 15:00 | Seminar room of physics (106)
The meeting will take place in the seminar room of physics (room 106).

Maciej Kierkla: Conformal model for gravitational waves and dark matter. A status update
2023-01-12 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
We present an updated analysis of the first-order phase transition associated with symmetry breaking in the early Universe in a classically scale-invariant model extended with a new SU(2) gauge group.
Including recent developments in understanding supercooled phase transitions, we compute all of its characteristics and significantly constrain the parameter space. We then predict gravitational-wave spectra generated during this phase transition and by computing the signal-to-noise ratio we conclude that this model is well testable (and falsifiable) with LISA. We also provide predictions for the relic dark matter abundance. It is consistent with observations in a rather narrow part of the parameter space, as we exclude the so-called supercool dark matter scenario based on an improved description of percolation and reheating after the phase transition as well as inclusion of the running of couplings.
Finally, we pay special attention to renormalisation-scale dependence of the results and even though our main results are obtained with the use of renormalisation-group improved effective potential, we also present the outcome of a fixed-scale analysis. It proves that the dependence on the scale is not only qualitative but also quantitative.
https://indico.ijs.si/event/1555/

[Biophysics seminar] Jan Rozman: "Shape-tension coupling produces nematic order in an epithelium vertex model"
2023-01-10 14:00 | F1 tearoom
We study the vertex model for epithelial tissue mechanics extended to include coupling between the cell shapes and tensions in cell-cell junctions. This coupling represents an active force which drives the system out of equilibrium and leads to the formation of nematic order interspersed with prominent, long-lived +1 defects. The defects in the nematic ordering are coupled to the shape of the cell tiling, affecting cell areas and coordinations. This intricate interplay between cell shape, size, and coordination provides a possible mechanism by which tissues could spontaneously develop long-range polarity through local mechanical forces without resorting to long-range chemical patterning.

The seminar will take place in the tearoom of the F1 department.

[Biophysics journal club] Domen Vaupotič: "Elastic properties and shape of the Piezo dome underlying its mechanosensory function"
2023-01-05 14:00 - 15:00 | Seminar room of physics (106)
We will be discussing the following paper: https://www.pnas.org/doi/full/10.1073/pnas.2208034119 (“Elastic properties and shape of the Piezo dome underlying its mechanosensory function”).

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

Jure Zupan: TBA
2022-12-22 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
https://indico.ijs.si/event/1549/

6th Trilateral meeting
2022-12-20 10:00 - 16:00 | Velika predavalnica IJS (IJS)
The trilateral meetings are a series of one day events designed to strengthen the scientific relations in particle, astroparticle physics and cosmology between Trieste, Nova Gorica and Ljubljana.
The 6th event will take place at the Jožef Stefan Institut in Ljubljana.
The program:
09:30 — 10:00: Welcome Coffee
10:15 — 11:00: Aleks Smolkovič: “Smelli Tails: Rare $b$ decays and high-mass Drell-Yan in the SMEFT” (35′ + 10′)
11:00 — 12:00: LHCb CERN Seminar ($R_K$ update) (indico here)
12:00 — 14:00: Lunch
14:00 — 14:30: Coffee
14:30 — 15:15: Jan Hajer: “Pseudo-Dirac heavy neutrinos in low scale seesaw models” (35′ + 10′)
15:15 — 16:00: Jure Zupan: “Neutrino polarizability” (35′ + 10′)
Organizing committee:
Aleksandr Azatov (SISSA)
Nejc Košnik (IJS)
Jonathan Kriewald (IJS)
David Marzocca (INFN)
Miha Nemevšek (IJS)
Andrea Romanino (SISSA)
Michele Tammaro (IJS)
Lorenzo Ubaldi (Uni Genova & INFN)
Gabrijela Zaharijas (UNG)
Past meetings
Trieste Meeting, Thursday 23 Jun 2022, at IFPU
Nova Gorica meeting, 15 September 2021 at Vipava
Ljubljana meeting, 16 December 2021 at IJS
Trieste meeting, 5 February 2020, at IFPU
Ljubljana meeting, 17 October 2019, at IJS

https://indico.ijs.si/event/1559/

16th Xmas Biophysics Workshop
2022-12-12 10:00 - 2022-12-13 14:00 | Elegans Hotel Brdo, Predoslje 39, Kranj, 4000, Slovenia
The 16th Xmas Biophysics Workshop returns the series to the old tracks and will take place on December 12th and 13th at Elegans Hotel in Brdo, Slovenia. The workshop traditionally brings together researchers in biophysics from Croatia, Italy, Austria, Slovenia, and other countries in the region.

Visit the workshop webpage for program, registration, and other details: xbw2022.ijs.si

Fotis Koutroulis: Thermal effects in Ising Cosmology
2022-12-08 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
Abstract:
We consider a real scalar field in de Sitter background and compute its thermal propagators. Using arguments from holography we propose, in a dS/CFT context, that non-trivial thermal effects as seen by an ‘out’ observer can be encoded in the anomalous dimensions of the d = 3 Ising model. One of these anomalous dimensions, the critical exponent η, fixes completely a number of cosmological observables and is almost entirely responsible for the deviation of the cosmological spectral index nS of scalar fluctuations from unity.
A connection with standard Inflation may be possible at the late time regimes where the time-dependent part of the field dominates.
https://indico.ijs.si/event/1570/

Emmanuel Ortiz Pacheco: TBA
2022-12-08 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
https://indico.ijs.si/event/1487/

Axel Maas: New effects in precision Brout-Englert-Higgs physics
2022-12-01 11:15 - 12:15 | Z9/0-0 – F1 čajnica (Jamova)
Since more than 40 years several formal results hinted for additional effects beyond perturbation theory even at weak coupling in theories with a Brout-Englert-Higgs effects. In this talk analytical and lattice results are presented for processes, like vector boson scattering and lepton colliders, demonstrating that these effects are present and possibly detectable in experiments. Furthermore, in many BSM scenarios the same effects yield qualitative, rather than quantitative consequences, as will be briefly surveyed.
https://indico.ijs.si/event/1506/

[Biophysics seminar] Matej Kanduč: "What can we learn from chicken eggs about polymer transitions?"
2022-11-30 15:00 - 16:00 | F1 tearoom
Polymer brushes with stimuli-responsive properties have attracted substantial research interest in the past few years, as they offer a wealth of opportunities to design materials that trigger structural and physico-chemical changes as a response to applied external stimuli. I will discuss our current experimental/theoretical study on conformational changes in nonionic polymer brushes induced by hydrostatic pressure and temperature variations. Interestingly, we can learn a lot about these polymers from our everyday food – eggs.

[Biophysics journal club] Veronika Bukina: "Packaging-signal mediated assembly of phage MS2"
2022-11-24 14:00 - 15:00 | Seminar room of physics (106)

Davide Dal Cin: Planck-Scale Physics and the Peccei-Quinn inflation model
2022-11-24 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
The radial direction of the Peccei–Quinn field can drive cosmic inflation, given a non-minimal coupling to gravity. This scenario has been considered to be capable of explaining inflation, the strong $CP$ problem, and dark matter. We argue that Peccei–Quinn inflation is extremely sensitive to higher-dimensional operators. Further combining with the discussion on the axion quality required to solve the strong $CP$ problem, we examine the validity of this scenario. We also show that a resonant amplification of the axion field is unavoidable after Peccei–Quinn inflation.
https://indico.ijs.si/event/1501/

Martín Novoa-Brunet: Probing CP violation in semi-leptonic b-decays through time-evolution
2022-11-21 11:15 - 12:15 | Z9/0-0 – F1 čajnica (Jamova)
We discuss the role of time-dependent observables in probing CP-violation in b –> s l+ l- and b –> s nu nubar decays. We identify a set of new observables by looking at the time evolution of the differential decay rate of B_d,s –> P(S) l+ l- and B_{d,s} –> P(V) nu nubar where the interference of B_{d,s}-barB_{d,s} meson mixing and decay is probed. We show that these observables do not require a time-dependent analysis but could be obtained by time-integrated or time-asymmetries if flavour tagging is available.
These observables are precisely predicted in the SM, are unaffected by NP in models with real contributions to SM and chirally flipped operators, are independent of form factors and are unaffected by hadronic uncertainties. They are however sensitive probes of NP scenarios involving new CP-odd phases.
https://indico.ijs.si/event/1563/

[Biophysics Journal Club] Matej Krajnc: "Modeling epithelial tissues as active-elastic sheets"
2022-11-17 14:15 - 15:00 | Seminar room of physics (106)

Tim Höhne: Vector-like Fermion Portals into Higgs Stability
2022-11-17 11:15 - 12:00 | Z9/0-0 – F1 čajnica (Jamova)
We address the notorious metastability of the standard model (SM) Higgs potential and promote it to a model building task: What are the new ingredients required to stabilize the SM up to the Planck scale without encountering subplanckian Landau poles? Using the SM extended by vector-like fermions, we chart out the corresponding landscape of Higgs stability. We find that the gauge portal mechanism, triggered by new SM charge carriers, opens up sizeable room for stability in a minimally invasive manner.
We also find models with Yukawa portals into Higgs stability opening up at stronger coupling. Several models allow for vector-like fermions in the TeV-range, which can be searched for at the LHC. For nontrivial flavor structure of Yukawa couplings severe FCNC constraints arise which complement those from stability, and push lower fermion masses up to O(10^3 TeV).
https://indico.ijs.si/event/1523/

Luiz Vale Silva: New physics in meson mixing
2022-11-14 11:15 - 12:15 | Z9/0-0 – F1 čajnica (Jamova)
The mixing of neutral mesons has been playing a key role in the formulation and testing of the Standard Model. It is also sensitive to some of the highest Beyond the Standard Model scales probed in laboratory experiments. In light of the planned LHCb Upgrades, Belle~II and its possible upgrade, and the broad interest in flavour physics in the tera-$Z$ phase of the proposed FCC-$e e$ program, I discuss constraints on New Physics contributions to $B_d$ and $B_s$ mixing which can be obtained in these benchmark scenarios. Then, I discuss the leading-order renormalization of double-insertions of dimension-6 four-fermion operators that change quark flavor by one unit (i.e., $ | Delta F | = 1 $, $ F = $ strange-, charm-, or bottom-flavor), by dimension-8 operators relevant to meson mixing (i.e., $ | Delta F | = 2 $) in SMEFT, setting then bounds on the Wilson coefficients of operators of dimension-6.
https://indico.ijs.si/event/1556/

[Biophysics seminar] Maria Pedrosa Bustos: "Langmuir monolayers as membrane models to study anticancer drugs"
2022-11-10 14:00 - 15:00 | F1 tearoom
When designing novel anticancer drugs, it is crucial to analyze how they interact with cell membranes. For this purpose, Langmuir monolayers have been widely used to mimic half of a cell membrane under controlled conditions. In this study, healthy and tumor cell membranes are emulated using different mixtures of phospholipids and cholesterol. Their interaction with a model anticancer drug (curcumin) is analyzed experimentally by means of a Langmuir through. These studies are complemented by molecular dynamics simulations, which offer additional molecular-level insight into the drug-monolayer interactions.

The meeting will take place in the tearoom of the F1 department.

Sašo Grozdanov: Journal club on "Noninvertible Global Symmetries in the Standard Model"
2022-11-10 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (Zoom)
Journal club presentation by Sašo Grozdanov on Y. Choi, H. T. Lam, S.-H. Shao, Noninvertible Global Symmetries in the Standard Model, Phys. Rev. Lett., 129, 161601 (2022)

https://indico.ijs.si/event/1558/

Luiz Vale Silva: TBA
2022-11-10 11:15 - 12:15 | https://zoom.us/j/3601731049?pwd=[REDACTED] (F1 tea room)
https://indico.ijs.si/event/1554/

[Biophysics journal club] Marin Šako: "Tensile strength of water"
2022-10-24 11:00 - 12:00 | F1 tearoom

[Biophysics seminar] Matej Kanduč: "Monolayer Adsorption Versus Bulk Micellization: Insights from Molecular Simulations"
2022-10-20 14:00 - 15:00 | Seminar room of physics (106)
Adsorption of amphiphilic molecules to aqueous interfaces occurs in many technological and biological settings, sometimes desired (stabilization of foams), while other times not (contamination). I will discuss how atomistic computer simulations can help us elucidate molecular mechanisms of surfactant adsorption, ranging from short-chain alcohols to double-tail lipids.
Small surfactants form loose monolayers and exhibit rapid exchange between the interface and bulk, which can be followed in the simulations.
Surfactants with longer alkyl chains adsorb as denser monolayers and exchange on experimental timescales that are too slow to be captured in simulations, which challenges molecular modeling. The modeling of this regime requires advanced computational techniques that connect interface and bulk phases via precise determinations of their chemical potentials.
Finally, double-chain surfactants (also called “lipids”) do not exchange between bulk and interface both on experimental and simulation timescales. They exist as bilayer aggregates already in solution and adsorb to surfaces in the form of monolayers only under certain conditions. As it turns out, a universal determiner for adsorption is the wetting contact angle of the surface. Only surfaces with contact angles larger than around 60-70° are capable of forming lipid monolayers.
