This short review is devoted to the celebration of two major events in quantum physics. The first one is the birth of the concept of Bose–Einstein condensation (1925) and the second is the experimental proof that it does exist and appears in liquid 4He simultaneously with superfluidity below the λ-point (1975).
Both of these events are tightly related to the Bogoliubov theory of superfluidity (1947). The existence of condensate in the system of interacting bosons is the key ansatz of this theory. Therefore, the experiments started at JINR-Dubna in 1975 confirmed this prediction of the Bogoliubov theory that superfluidity of liquid 4He (He II) should emerge at the same time as the Bose–Einstein condensation.
Corrected:
13 November 2025 (the captions to Figures 1 and 2 were changed)
26 November 2025 (changes were made in formulas (53) and (55))
We consider a complex rational degeneration of the hyperbolic Ruijsenaars model emerging in the limit ω1 + ω2 → 0 (or b → i in 2d CFT) and investigate the two-particle case in detail. Corresponding wave functions are described by complex hypergeometric functions in the Mellin–Barnes representation. Their dual integral representation and reflection symmetry in the coupling constant are established. Besides, a complex limit of the hyperbolic Baxter Q-operators is considered. Another complex degeneration of the hyperbolic Ruijsenaars model is obtained by taking a special ω1 − ω2 → 0 (or b → 1) limit. Additionally, two new degenerations to the complex Calogero–Sutherland type models are described.
For the reconstruction problem, the universal representation of inverse Radon transforms implies the needed complexity of the direct Radon transforms which leads to additional contributions. In the standard theory of generalized functions, if the outset (origin) function which generates the Radon image is a pure-real function, as a rule, the complexity of Radon transforms becomes in question. In the paper, we discuss the Fourier slice theorem analyzing the degenerated (singular) points as possible sources of the complexity. We also demonstrate different methods to generate the needed complexity at the intermediate stage of calculations. Besides, we show that the introduction of the hybrid (Wigner-like) function ensures naturally the corresponding complexity. The discussed complexity not only provides the additional contribution to the inverse Radon transforms, but also makes an essential impact on the reconstruction and optimization procedures within the framework of the incorrect problems. The presented methods can be effectively used for the practical tasks of reconstruction problems.
The near neutrino detector ND280 of the long-baseline accelerator experiment T2K has been upgraded to improve the precision of measurement of the neutrino oscillation parameters. A key component of the upgrade is a novel segmented plastic scintillator detector, Super Fine Grained Detector (SuperFGD), made of approximately 2 million optically isolated 1 cm3 cubes read out by three orthogonal wavelength-shifting fibres and multi-pixel photon counters. The SuperFGD provides 3D images of neutrino interactions by tracking the final-state charged particles including protons down to a threshold of about 300 MeV/c. Due to the fine segmentation and the sub-nanosecond time resolution, the SuperFGD is able to detect neutrons from neutrino interactions and to reconstruct their kinetic energy by measuring the time of flight. In this paper, the details of the detector design, construction and performance in the T2K neutrino beam are described.
In this work, the characteristics of a prototype SPECT system based on the Timepix readout chip, with a MURA-type encoding mask, were evaluated. The setup has a small FoV and can be used in preclinical studies of drugs on small laboratory animals. Despite many existing test protocols developed and described in pertinent documents of national standard bodies and IAEA recommendations, they are not suitable for microtomographic systems based on semiconductor pixel detectors due to different detector technology, high spatial resolution and small area of interest. To measure their characteristics, special phantoms were developed, with a small “hot region”.
Such micro-SPECT parameters as spatial resolution, contrast, linearity, and system efficiency were studied using 99mTc source. The detector calibration and data preprocessing are described.
The problem of identifying and extracting the dynamic variables associated with symmetry transformations from the full set of dynamic variables is considered. It is demonstrated that employing a boson representation of bifermion operators enables the problem to be solved using the canonical transformation of dynamic variables proposed by N. N. Bogoliubov. The results obtained justify the application of the cranking model for the description of the rotational excitations of nuclei.
The accelerator complex NICA is at the stage of assembling and commissioning. A series of successful runs at the injection complex were carried out using various types of ions. It is planned to continue the linear optics measurements at booster synchrotron, for which several methods are considered. The first one is based on the analysis of turn-by-turn data of the beam orbit going from beam position monitors. The independent component analysis is used for the data processing and results to computation of betatron and synchrotron tunes, beta-functions, phase advances and dispersions. Other methods use orbit response matrix measured with alternate kicks by dipole correctors. Accuracy of optics restoration depends on the technical feasibility of betatron tunes and orbit measurements. Various methods should be firstly accommodated to the accelerator and tested using computational model in order to conclude their potentials and form requirements for future experiments with the beam. The paper describes implementation of independent component analysis to the computer model of the NICA Booster.
Using the generalized renormalisation group formalism, we calculate quantum corrections to the effective potential in α-attractor models describing the inflationary stage of the Universe evolution. We demonstrate that quantum corrections lead to a change in the initial classical potential, changing its value at the minimum, which can be interpreted as a manifestation of the cosmological constant or dark energy.