arXiv subjects

Yuriy Bidasyuk

Publications and source records attributed to Yuriy Bidasyuk.

5 recordsLinked to original sources

arXiv2026

Josephson spectroscopy in a circular atomic tunnel junction with acceleration-induced symmetry breaking

We study Josephson dynamics in a long atomic Bose-Josephson junction formed by two tunnel-coupled coplanar Bose-Einstein-condensate rings. An in-plane linear acceleration breaks the axial symmetry of the trap and transforms a single Josephson plasma oscillation into a multimode population-imbalance response. Gross-Pitaevskii simulations and Bogoliubov-de Gennes analysis show that the additional spectral components arise from collective modes that acquire finite overlap with the population-imbalance operator under symmetry breaking, with their activation governed by reflection symmetry about the acceleration direction. We also propose a mode-resolved Josephson-spectroscopy protocol based on a weak localized periodic perturbation. Frequency scans reveal resonant amplitude peaks and phase shifts at the eigenfrequencies of active Bogoliubov modes, while angular scans of the drive position provide access to the angular structure of the corresponding mode density perturbations. A dissipative time-dependent Bogoliubov theory yields analytical response functions in quantitative agreement with full Gross-Pitaevskii simulations in the linear regime. Our results demonstrate that accelerated dual-ring condensates provide a controllable platform for symmetry-selected Josephson dynamics and spectroscopic probing of collective modes.

cond-mat.quant-gas↗

arXiv2025

AGN spectral variability across activity states and searches for axion-like particles

Axion-like particles (ALPs) are compelling candidates for dark matter and potential portals to new physics beyond the Standard Model. Photons traversing magnetized regions can convert into ALPs, producing characteristic, energy-dependent absorption features in astrophysical spectra. The probability of such conversions depends sensitively on both the photon energy and the properties of the intervening magnetic fields. Most existing searches have focused on individual astrophysical sources, but uncertainties in the structure and strength of cosmic magnetic fields have limited their reach. Recently, we have demonstrated that active galactic nuclei (AGNs) observed through galaxy clusters provide especially promising targets for ALP searches. By stacking multiple AGN-cluster sightlines, one can average over poorly known magnetic field configurations in galaxy clusters and recover a distinctive ALP-induced spectral suppression, thereby significantly enhancing sensitivity. In this work, we investigate a possible systematic uncertainty in such analyses: the intrinsic time-variability of AGN spectra. We demonstrate that AGN flux variability is correlated with spectral hardness, and that time-averaging over flaring and quiescent states can potentially mimic the suppression features imprinted by ALP-photon mixing. Our findings imply that the recent constraints remain conservative, and that incorporating detailed spectral variability into stacking analyses can further sharpen the search for axion-like particles.

astro-ph.HE↗

arXiv2025

Active galactic nuclei through the prism of galaxy clusters: bounds on axion-like particles

Hypothetical axion-like particles (ALPs) are of interest because of their potential to act as dark matter or to reveal information about yet undiscovered fundamental constituents of matter. Such particles can be created when photons traverse regions of magnetic fields. The conversion probability depends on both the magnetic field parameters and photon energy, leading to multiple spectral absorption features as light passes through magnetized regions. Traditionally, astrophysical searches have focused on detecting such features in individual objects. However, the limited understanding of properties of cosmic magnetic fields have hindered the progress. Here we introduce a new approach by analyzing stacked (rather than individual) spectra of active galactic nuclei (AGNs) positioned behind galaxy clusters -- gigantic magnetic field reservoirs. Stacking efficiently averages over the uncertainties in magnetic fields, revealing a unique step-like spectral signature of photon-to-ALP conversion. With this approach we advance into previously inaccessible regions of the ALP parameter space for nano-electronvolt masses. Adopting this method will significantly improve existing bounds across a wide range of masses by using different telescopes and increasing the size of the stacked datasets. The Cherenkov Telescope Array Observatory, in particular, will extensively probe the parameter space where ALPs could serve as dark matter.

astro-ph.HE↗

arXiv2016

Stochastic phase slips in toroidal Bose-Einstein condensates

Motivated by recent experiments we study the influence of thermal noise on the phase slips in toroidal Bose-Einstein condensates with a rotating weak link. We derive a generalized Arrhenius-like expression for the rate of stochastic phase slips. We develop a method to estimate the energy barrier separating different superflow states. The parameters at which the energy barrier disappears agree with the critical parameters for deterministic phase slips obtained from dynamics simulations, which confirms the validity of our energetic analysis. We reveal that adding thermal noise lowers the phase-slip threshold. However, the quantitative impact of the stochastic phase slips turns out to be too small to explain the significant discrepancy between theoretical and the experimental results.

cond-mat.quant-gas↗

arXiv2011

Improved convergence of scattering calculations in the oscillator representation

The Schr\"odinger equation for two and tree-body problems is solved for scattering states in a hybrid representation where solutions are expanded in the eigenstates of the harmonic oscillator in the interaction region and on a finite difference grid in the near-- and far--field. The two representations are coupled through a high--order asymptotic formula that takes into account the function values and the third derivative in the classical turning points. For various examples the convergence is analyzed for various physics problems that use an expansion in a large number of oscillator states. The results show significant improvement over the JM-ECS method [Bidasyuk et al, Phys. Rev. C 82, 064603 (2010)].

physics.comp-ph↗