QFT | Science

Nature Astronomy | 15 August 2025

Constraints on axion-like particles from active galactic nuclei seen through galaxy clusters

Denys Malyshev, Lidiia Zadorozhna, Yuriy Bidasyuk, Andrea Santangelo & Oleg Ruchayskiy

"In our study, we used galaxy clusters as giant natural detectors to search for axion-like particles—one of the leading candidates for dark matter. By analyzing gamma radiation from distant active galactic nuclei shining through galaxy clusters, we looked for traces of photons converting into axions within the extensive magnetic fields of these clusters. Although the particles themselves remain elusive, we managed to establish the world's strictest constraints on the strength of their interaction with light. This narrows the permissible parameter space for theoretical models and determines priority directions for future experimental research aimed at uncovering the nature of dark matter."
Lidiia Zadorozhna, Junior Researcher at our department

Physical Review D | 23 July 2025

ACT observations, reheating, and Starobinsky and Higgs inflation

D.S. Zharov, O.O. Sobol, S.I. Vilchinskii

"In this work, we rescued the Starobinsky inflation model. The fact is, this model was proposed back in 1980 and, since then, has explained our observations more accurately than any other. However, in the fall of 2025, the Chilean ACT telescope published cosmic microwave background (CMB) observation results that excluded this model with a probability of over 95%. For us, it was a real scientific shock. Therefore, we decided to check what would happen if we supplemented it with a more precise reheating model. We found that with non-instantaneous reheating, the Starobinsky model still shows a high degree of consistency with observational data."
Dmytro Zharov, PhD Student at our department

Journal of High Energy Physics | 14 February 2025

On the Schwinger effect during axion inflation

Richard von Eckardstein, Kai Schmitz, Oleksandr Sobol

"Together with colleagues, we investigated the Schwinger effect during axion inflation, taking into account the non-collinearity of electric and magnetic fields in detail for the first time. We demonstrated that previous simplified calculations were off by more than a factor of 10 in estimating field strengths. This refinement is critically important for correctly predicting primordial gravitational waves and the formation of black holes in the early Universe."
Oleksandr Sobol, Research Partner of our department

Physical Review B | 25 August 2025

Viscoelastic tensor and hydrodynamics of altermagnets

A.A. Herasymchuk, E.V. Gorbar, P.O. Sukhachov

"In our work, we investigated the hydrodynamics of altermagnets—a novel class of magnetic materials combining the properties of ferro- and antiferromagnets. By calculating the viscoelasticity tensor, we showed that due to the specific anisotropy of Fermi surfaces in these systems, unique viscosity coefficients emerge, forcing the spin current to flow like a viscous fluid with a characteristic Poiseuille profile.
Alongside the theoretical description, we proposed clear experimental markers—specific distributions of electric potential and streamlines—that will allow the observation of this new hydrodynamic regime in real nanostructures."
Eduard Gorbar, Professor at our department

Physical Review A | 14 April 2025

Acceleration-driven dynamics of Josephson vortices in coplanar superfluid rings

Yurii Borysenko, Nataliia Bazhan, Olena Prykhodko, Dominik Pfeiffer, Ludwig Lind, Gerhard Birkl, and Alexander Yakimenko

"In our study, we investigated special quantum objects called Josephson vortices—essentially tiny 'tornadoes' of atomic fluid that emerge in a system of two flat rings placed one inside the other, like a target. The main idea of our work was to understand how these vortices react if this 'target' is moved in one direction or another. We discovered that when we start moving this entire system faster, the vortices lose their symmetric equilibrium and begin to shift in a very specific way, reacting to every change in speed.It turned out that by observing the position and movement of these quantum 'tornadoes', we can measure exactly where and with what force the device is accelerating with remarkable precision. This discovery is incredibly important because it allows such atomic structures to be used as a basis for next-generation ultrasensitive sensors. For example, they could become the foundation for ultra-precise navigation systems or essential components of quantum computers, where controlling every particle movement is crucial."
Olena Prykhodko, Associate Professor at our department

Physical Review A | 6 May 2025

Vortex phases and domain walls in trapped spinor Bose-Einstein condensates with inhomogeneous spin-orbital-angular-momentum coupling

O. O. Prykhodko and L. V. Zadorozhna

"In this work, we explored a special state of matter—the Bose-Einstein condensate, which forms when atoms are cooled to near absolute zero, forcing them to move as one synchronized organism. The main idea of our experiment was to 'spin' this cloud of atoms using special, structured laser light. It turned out that under certain conditions, microscopic quantum vortices emerge inside this quantum fluid, and they don't just scatter randomly; they line up in a perfectly even ring that we called a 'vortex necklace'. This necklace acts as a domain wall—an invisible barrier dividing the cloud into two parts with completely different properties. Inside the ring, the atoms form a pattern of high and low-density stripes, while outside it, they behave entirely differently, moving at a constant speed around the center of the ring. It was extremely fascinating to discover that we can control the size of this ring and the very structure of the matter simply by changing the laser intensity. We even created a mathematical model that accurately describes these processes, allowing us to better understand how such structured light might be used in the future to create new types of quantum materials or ultra-sensitive sensors."
Olena Prykhodko, Associate Professor at our department

Early Universe Cosmology

Cosmology today is not merely a description of the Universe's evolution; it is the intersection of elementary particle physics, general relativity, and quantum field theory. It is here that we seek answers to how the fundamental laws of the microcosm determined the fate of cosmic megastructures.

● Challenges in Big Bang Theory and Inflationary Physics● Search for Dark Matter and Dark Energy● Statistical Analysis of Cosmological Observational Data

Black Hole Physics

The study of black hole physics is one of the highest priorities in modern fundamental theoretical physics. Within the research activities of our department, these objects are viewed not just as astrophysical phenomena, but as unique theoretical proving grounds for studying the extreme states of matter and spacetime, where the effects of classical gravity interact with the quantum laws of the microcosm.

● Primordial Black Holes● Laboratory Realization of Acoustic Black Holes● Hawking Evaporation and the Information Paradox

The Standard Model of Particle Physics and Its Extensions

The Standard Model (SM) is the theoretical foundation of modern physics, describing all known fundamental particles alongside the electromagnetic, weak, and strong nuclear interactions. Despite its incredible success in describing the vast majority of known phenomena, the SM does not explain the nature of dark matter, neutrino masses, or gravity. Our department investigates Beyond the Standard Model (BSM) physics—supersymmetry, Grand Unified Theories (GUTs), and multidimensional models—which are key to understanding the physics of the early Universe and building a unified theory of fundamental interactions

● Dark Matter Search within the SHiP Project● Modeling Neutrino Masses● Research on the Baryon Asymmetry of the Universe

Condensed Matter Theory and Macroscopic Quantum Phenomena

Condensed matter theory investigates the physical properties of many-particle systems, where collective behavior determines the macroscopic characteristics of matter. The main focus is on macroscopic quantum phenomena — superconductivity, superfluidity, and Bose-Einstein condensation — where quantum coherence encompasses a vast number of atoms, allowing quantum effects to be observed on macroscopic scales. Our research covers the study of topological phases of matter, strongly correlated systems, and quantum phase transitions, which form the foundation for the development of novel quantum technologies and materials science.

● Graphene Physics● Bose-Einstein Condensates● Superfluidity and Superconductivity

High-Energy Astrophysics, Data Analysis, and Multi-Messenger Observations

High-energy astrophysics views the Universe as a natural laboratory for extreme processes. Here, we study phenomena where particles and radiation reach energies unattainable in terrestrial accelerators: near black holes, neutron stars, magnetars, within the relativistic jets of active galactic nuclei, and during explosive transients. The primary focus is extracting information from large, complex, and statistically limited observational datasets.

It is here that data becomes the key to understanding the most extreme processes in the Universe — from particle acceleration mechanisms to the nature of dark matter and the origin of ultra-high-energy cosmic rays.

● Handling large observational and simulated datasets● Complex statistical analysis in low-count event regimes● Integrating various observational channels into a unified physical picture (Multi-messenger astronomy)● Searching for new physics and testing fundamental theories through astrophysical observations

Physics of Complex Systems

The physics of complex systems is an interdisciplinary field that investigates systems whose collective behavior differs significantly from the properties of their individual components. Research focuses on studying the effects of emergence, nonlinear dynamics, and self-organization that manifest across various scales: from quantum technologies to the large-scale structure of the Universe.

An important aspect of this work is the study of quantum fluids and Bose-Einstein condensates (BECs) as platforms for novel technologies. This direction includes creating laboratory analogues of black holes and investigating the nature of dark matter through the lens of superfluidity, particularly studying quantized vortex structures in self-gravitating media.

Our scientific work is based on combining the analytical methods of quantum field theory with powerful numerical simulations. This allows us to predict the behavior of systems under unpredictable external changes and discover universal laws governing the emergence of order from chaos.

● Quantum analogues of black holes in laboratories● Natural and artificial complex systems (Swarm AI)● Nonlinear dynamics and synergetics

Quantum Computing and Quantum Information

This field investigates the fundamental principles of acquiring, transmitting, and processing information using quantum-mechanical systems. The research spans the entire technology stack: from the physical realization of qubits to the development of high-level quantum algorithms.

We investigate the nature of physical systems capable of acting as carriers of quantum information (photons, cold atoms, superconducting circuits). Key attention is given to studying decoherence and dissipation processes, as well as developing methods for controlling quantum states to ensure the stable operation of quantum circuits.

Quantum entanglement is studied as a fundamental resource for building quantum teleportation algorithms. The work is also aimed at exploring measures of quantum correlation, entropic characteristics, and quantum error correction methods that ensure data stability during quantum computations.

● Developing quantum algorithms to solve problems inaccessible to modern supercomputers● Research in quantum artificial intelligence● Implementing quantum circuits in laboratories