Physics of Particles and Nuclei最新文献

At the initial stage of its development, general relativity (GR) was verified and confirmed in a weak gravitational field limit. However, with the development of astronomical observation technologies, GR predictions in a strong gravitational field began to be discussed and confirmed, such as the profile of the X-ray iron (Kalpha ) line (in the case if the emission region is very close to the event horizon), the trajectories of stars near black holes and the shapes and sizes of shadows of supermassive black holes in M87* and Sgr A*. In 2005 it was predicted that a shadow formed near a supermassive black hole at the Galactic Center could be reconstructed from observations of ground based global VLBI system or ground—space interferometer acting in mm or sub-mm bands. In 2022 this prediction was confirmed since the Event Horizon Telescope (EHT) collaboration reported about a shadow reconstructions for Sgr A*. In 2019 the EHT collaboration presented the first image reconstruction around the shadow for the supermassive black hole in M87. In 2021 the EHT collaboration constrained parameters (“charges”) of spherical symmetrical metrics of black holes from an allowed interval for shadow radius. In 2022 the EHT collaboration constrained charges of metrics for the supermassive black hole at the Galactic Center. Earlier, we obtained analytical expressions for the shadow radius as a function of charge (including a tidal one) in the case of Reissner–Nordström metric. Based on results of the shadow size evaluation for M87* done by the EHT collaboration we constrained a tidal charge. We discussed opportunities to use shadows to test alternative theories of gravity and alternative models for galactic centers.

The basic properties of the confinement mechanism in QCD—the temperature dependence of the spatial and temporal string tensions (({{sigma }_{{text{s}}}}(T)) and ({{sigma }_{{text{E}}}}(T)))—are studied in the framework of the Field Correlator Method (FCM). It is shown that both functions are connected respectively to the spatial and temporal parts of the vacuum gluon energy ({{epsilon }_{{text{s}}}}) and ({{epsilon }_{{text{E}}}}) which define their equal values at (T = 0). However at (T > 0) the spatial part is growing with T while the temporal part is destroyed by the hadronic pressure at (T = {{T}_{{text{c}}}}) (the deconfinement). Both properties are derived within the same method and are in a good agreement with the corresponding lattice data.

A physical model based on the hypothesis of the existence of a photon superstar is considered. This model is shown to be capable of describing gravity and quantum phenomena from a unified position.

A brief overview of the development of theoretical approaches to describing the structure of heavy atomic nuclei is given. Both shell model and collective nuclear model are considered. Great attention is paid to the symmetries presented in these models. Approaches based on nucleon–nucleon interaction are discussed in detail.

A review of the results of research at the SSC RF-IPPE accelerator complex, conducted to study the phenomenon of delayed neutron (DN) emission in the fission of heavy nuclei by neutrons, is presented. Experimental data on the macroscopic DN characteristics are considered, which are of paramount importance for safe operation of nuclear reactors: the total DN yield and the DN time parameters (relative yields of DN and half-lives of their precursors), the integral DN energy spectra for the ²³⁵U fission by thermal neutrons and the DN 8-group spectra obtained on their basis. The procedure for the estimation of the DN time parameters and their covariance matrices are considered. The data obtained are compared with the data obtained by other authors. This review does not include the works of the authors devoted to developed physical methods for studying the physics of fission of heavy nuclei by neutrons based on detecting delayed neutrons, as well as works related to the physical interpretation of the results obtained. Only a brief list of them is provided with appropriate references.

An overview of the results obtained within the framework of the JINR-UNISA collaboration in the field of theoretical study of of Josephson nanostructures is presented. In particular, our work has involved studies of a wide variety of nonlinear dynamic effects in various systems of coupled Josephson junctions, including superconductor/ferromagnet/superconductor junctions, which are currently being investigated intensively due to the potential applications is superconducting spintronics.

Within the conserving Φ-derivable and virial approaches to equilibrium dilute strongly-interacting systems we study a system of non-relativistic fermions of one kind (e.g., neutron matter) interacting via a pair potential in the limit (n{{lambda }^{3}} ll 1), where n is the fermion number density and λ is the thermal wavelength. The variety of potentials of the quantum and classical origin is used for the quantitative comparison of results obtained within both approaches. In all cases relevant to the nucleon-nucleon interaction, the attraction volume of the interaction is larger than the repulsion one. General properties of the Φ derivable approach are studied. Expressions for the second and third virial coefficients are derived and analyzed for the Φ functional including the tadpole and sandwich diagrams. The classical high-temperature limit of the Φ functional is reproduced by the tadpole diagram. Next, classical, semiclassical (up to order ({{hbar }^{3}})), and purely quantum (Beth-Uhlenbeck) virial expansions of the equation of state are studied. Various extrapolations of the virial equation of state are considered including the van der Waals form and the excluded volume models. We derive the expression for the second virial coefficient within the effective range approximation for the scattering amplitude. Comparison with purely quantum Beth–Uhlenbeck result employing experimental phase shifts shows approximate agreement for low temperatures, (T lesssim 20) MeV. Then, we study the problem of the anomalously large empirical value of the nucleon-nucleon scattering length, appearing due to existence of the quasi-bound state in nucleon-nucleon scattering. The latter is destroyed already in a dilute matter due to the Pauli blocking. Subtracting the quasi-bound state term, we show that the second virial coefficient has the same low temperature dependence as one obtained within the Φ derivable approach in the Born approximation. Also, we discuss origins of differences arising beyond the region of the common validity of the Φ derivable and virial approaches.

The review describes the results of experiments based on quite different and independent approaches to solving the problem of interaction of muons with nuclei. Different paths of muon capture by nuclei and subsequent paths of secondary processes are considered: radiationless capture followed by nuclear fission, excitation of the nucleus with the escape of particles (neutrons and charged ones), and excitation of nuclear levels with the escape of gamma quanta. The experimental data require refinement, in particular with respect to the spectroscopy of fission fragments, the spectroscopy of secondary particles, and statistical accuracy. All of the experimental methods described rely on interpretation within theoretical models. Improvement in each of these parts will mutually stimulate refinements or new paths in subsequent research. The article is addressed to young aspiring physicists interested in muon physics and looking for new phenomena of interactions of elementary particles with nuclei and atoms, and solutions to emerging problems using modern experimental methods.