Theory of Nuclear Systems

Participating Countries and International organizations:

Armenia, Belarus, Belgium, Brazil, Bulgaria, China, Czech Republic, Egypt, France, Germany, Greece, Hungary, India, Iran, Italy, Japan, Kazakhstan, Lithuania, Mexico, Norway, Poland, Republic of Korea, Romania, Russia, Serbia, Slovakia,
South Africa, Spain, Sweden, Ukraine, United Kingdom, USA, Uzbekistan.

The problem under study and the main purpose of the research:

The theme proposes to research and develop ways to solve current problems in nuclear physics, relativistic nuclear physics, nuclear astrophysics, in the field of quantum few-body systems, and nonlinear quantum processes. Researches will be closely coordinated with experimental programs at facilities that exploit high-intensity beams of stable and/or radioactive ions at JINR (SHE-factory, ACCULINA-2) and worldwide (FAIR, ISOL facilities, SPES, SPIRAL2, FRIB, RAON, HIAF, iThemba LABS, ELI-NP). Studies of collisions of high-energy heavy ions and the phenomenon of color transparency will be associated with the NICA project at JINR. Large-scale studies of the structure of exotic nuclei, the dynamics of nuclear reactions, properties and methods of obtaining superheavy nuclei are planned. The task is to include dissipation and diffusion in the dynamics of the nucleus-nuclear interaction and preserve the essence of the quantum multiparticle nature of colliding nuclei. The study of systems with a small number of particles is also necessary in order to describe resonant processes in nuclear physics and high-energy physics. Studies of nonlinear quantum processes in very strong polarized electromagnetic fields, which are achieved in short high-frequency laser pulses, are of interest.

Brief annotation and scientific rationale:

The scientific Project aims to solve a fundamental task of contemporary nuclear physics – development and improvement of a
self-consistent microscopic approach to describe the structure of ground and excited states of exotic and superheavy atomic nuclei, as well as to predict their decay properties. On the one hand, such an approach is necessary for planning the research program of modern heavy ion accelerator facilities (SHE-Factory at JINR, SPIRAL2 at GANIL, FAIR at GSI, RIBF at RIKEN) and for interpretation of their results. On the other hand, the need for reliable theoretical nuclear data is also relevant for modeling various astrophysical processes.

The self-consistent microscopic approach used in the Project to describe ground and excited nuclear states is based on the combination of the energy density functional (EDF) method and the quasiparticle-phonon nuclear model (QPM). The EDF has proven itself in global calculations of nuclear characteristics and in astrophysics. The use of the coupling of simple and complex configurations in the framework of QPM is nowadays practically the only way allowing one to go beyond the harmonic approximation using large configuration space without violating the Pauli principle.

Expected results upon completion of the project:

The form and parameters of the EDF will be extrapolated far beyond the stability valley. Special attention will be paid to isovector properties, which play a crucial role in nuclei with large neutron-proton asymmetry.

Using a unified set of EDF parameters, the effect of interaction between simple and complex configurations on the properties of charge-neutral and charge-exchange nuclear excitations will be investigated with respect to their resonance structure as well as on the decay characteristics of nuclei at the driplines.

The developed self-consistent EDF+QPM framework will be applied to study β-decay in the context of astrophysical r-process and weak nuclear reactions with hot nuclei in various astrophysical scenarios (supernova explosions, stellar nucleosynthesis, neutrino emission).

Prediction of α spectra of superheavy nuclei for planning future experiments. α-decays from isomeric states as well as fission from these states will be considered.

In order to determine the competition between different modes of radioactive decay of superheavy nuclei, lifetime calculations concerning orbital electron capture and β⁺-decay will be carried out.

Analysis of the evolution of magic numbers as a function of the ratio of neutron to proton numbers in the nucleus and prediction of new nuclei with closed (sub)shells near the proton and neutron driplines.

Study of the role of tensor interaction in the fragmentation of the Gamow-Teller resonance and beta-decay of exotic nuclei.

Investigation of neutrino interaction with matter that is important in various astrophysical phenomena, e.g., supernovae, neutron star mergers, etc. The role of inelastic neutrino scattering on nuclei and the magnetic field in the neutrino thermalization process must be elucidated.

Calculations of charge and matter distribution radii for long isotopic chains, including deformed nuclei. Theoretical analysis of isotopic behavior of radii and observed anomalies.

Expected results of the project in the current year:
Investigation of low-energy states in No isotopes within the self-consistent random-phase-approximation with Skyrme forces.

Theoretical analysis of E1 and M1 excitations in deformed nucleus ¹⁵⁶Gd.

Fayans functional: consideration of relativistic corrections in the equations of state for symmetric nuclear and purely neutron matter. 

Calculations of magnetic moments for the ground and isomeric states in long isotopic chains.

Refinement of conditions for the formation of superconducting pair correlations in spherical even-even atomic nuclei.

Study of the relationship between the double gamma decay of quadrupole states and the fine structure of the giant dipole resonance.

Analysis of the electric and magnetic dipole transitions in medium and heavy nuclei.

Study of the rigid- and irrotational-flow quadrupole dynamics of weakly deformed nuclei within the microscopic shell-model version of the Bohr-Mottelson model.

Study of the scissors mode in the even-even superheavy nuclei by the Wigner function moments method.

Calculation of the contribution of forbidden transitions into EC/β⁺-decay of odd-odd nuclei in the α-decay chain of ²⁸⁸Mc.

Brief annotation and scientific rationale:

The purpose of the project is to study the important dynamical nuclear processes such as fusion, quasifission, multinucleon transfers, capture and breakup. Investigations of the near threshold effects demand uniform description of the nuclear structure and reactions. Priority will be a development of cluster models that allow us to reveal peculiarities of the nuclear structure at extreme excitatios. A further development of the completely quantum models for decays of weakly bound nuclei is planned. The transport coefficients and nucleus-nucleus potentials calculated microscopically would be used in the double-folding model for a description of the fusion dynamics.

It is necessary to study in detail the influence of the environment on the rate of astrophysical reactions. This demands further development of the theory of the quantum systems. Thus, it is necessary to consider low-energy dipole excitations that play presumably a noticeable role in stellar nucleosynthesis.

Study of the nuclear properties depending on an energy is necessary to reveal effects outside the mean field description. In heated nuclei, the potential energy surface changes in such a way that the height of the fission barrier for superheavy nuclei decreases. Therefore, investigations of the shell effects damping with increasing energy are important for estimation of the stability of excited heavy nuclei.

Exploring the formation of superheavies with Z=119 and 120 in fusion reactions must be continued within a microscopic approach. Also, the peculiarities of the quasifission competing with the complete fusion will be considered. There are plans to compare the calculated mass distributions and TKE of the quasi-fission products with distributions of the fission products. New heavy ion isotopes, which cannot be obtained in the complete fusion reactions, can be formed by transfer reactions. Therefore, further theoretical analysis of these reactions by including a cluster transfer into the description is required. Investigations of the synthesis of new isotopes of superheavy nuclei must be continued in the evaporation channels of charged particles in order to search for the most suitable reactions for future experiments.

The advantage of the cluster approach is the simultaneous description of α-decay and spontaneous fission from the ground state of both even-even and even-odd nuclei with the same set of parameters. The main model assumption is that charge asymmetry as a collective coordinate is responsible for these processes. In the same approach, it is necessary to investigate fission from isomeric states and induced fission. Success in describing experimental data will lead to a new insight into fission process.

Expected results upon completion of the project:

Creation of new theoretical approaches and models for description and prediction of the properties of unstable nuclei and exotic nuclear systems and their application to astrophysical problems. 

Explanation of the reaction mechanism with particles and nuclei within the broad energy interval.

Exploring the limits of nuclear stability, positions of proton and neutron drip-lines, detection of proton shell closure beyond Pb, and the best way to produce a certain isotope.

Study of fusion and fission dynamics providing benchmarks for confirming certain ways of fusion and fission.

Investigation of the influence of the environment on astrophysical reactions.

Study of the nuclear structure change with temperature and angular momentum, the role of cluster degrees of freedom in nuclear excitations, and the properties of superheavies.

Exploration of the properties of nuclear systems beyond the nucleon stability, the multineutron radioactive decay existence.

Expected results of the project in the current year:

Application of the collective Hamiltonian with an isovector pair and alpha-particle type correlations to describe the ground-state energies of even-even and odd-odd nuclei around ⁵⁶Ni.

Investigation of the structure of the superheavy nuclei belonging to the alpha-decay chain of ²⁸⁸Mc. 

Description of low-lying spectra of heavy nuclei using the collective equation obtained in the framework of the generator coordinate method and potentials calculated in the mean-field approximation.

Calculation of the properties of nuclei involved in nucleon transfer reactions leading to the synthesis of new isotopes. Investigation of the production of neutron-deficient isotopes of actinides.

Application of the DNS model to describe fusion-fission and quasifission reactions leading to actinide compound nuclei.

Solution of master equations that describe the fission of highly excited rotating heavy compound nuclei. 

Description of the changes in the half-live times of shape isomers due to excited cluster states. 

Description of the mass distributions and rate of ternary fission in nuclei near Z=100 with inclusion of the octupole deformation of fission fragments at the scission point.  

Investigation of the fine structure of alpha-decay for different isotopes of Ra, Th, U, and Pu nuclei and study of the role of angular momentum dependence of the spectroscopic factors.

 Calculation of the spectra of collective excitations of fissile nuclei at the scission point within the DNS model and analysis of the angular anisotropy of fission fragments in neutron-induced fission of various U and Pu isotopes. 

Study of the structure of the heavy hydrogen ⁷H in the ⁸He(p,2p) reaction, taking into account peculiarities of the reaction mechanism and the structure of ⁸He. 

Study of the properties of giant monopole and quadrupole resonances within the Random Matrix approach. 

Study of the effects of spin-orbit interaction on the transport properties of nanosystems. 

Investigation of the impact of axial asymmetry on the state density and entropy along the fission paths of superheavy nuclei, e.g., ²⁹⁶Lv by using the statistical method.

Calculation of neutron multiplicities, kinetic energy and mass distributions of fission fragments in spontaneous fission of transfermium nuclei with allowance for the evolution of the dinuclear system at the scission point. 

Сalculation of the yields of ²⁰⁹Bi(γ,xn) photonuclear reactions and analysis of the role of pre-equilibrium neutron emissions. 

Estimation of the contributions of the differential cross sections to the formation of reaction products of deep inelastic collisions, incomplete fusion and quasifission in the reactions ³⁶Ar+¹⁴⁴Sm, ⁶⁸Zn+¹¹²Sn and ⁹⁰Zr+⁹⁰Zr. 

Study of excitation energy dependence of potential energy surface for the heaviest nuclei. 

Study of the role of various evaporation channels in Pb- and Bi-based fusion reactions.

Brief annotation and scientific rationale:

The project is aimed at studying systems formed by a small set of constituents of nuclear, subnuclear or atomic-molecular origin. The smallness of the number of constituents in a system allows one to develop and use mathematically rigorous, precise and consistent approaches to its investigation, the approaches that do not require further simplifying physical assumptions and approximations. The goal of the project consists in developing and improving the methods of numerical solving of few-body problems in nuclear, atomic and molecular physics, and astrophysics. The developed approaches and methods will be employed in the numerical study of various concrete few-body quantum systems.

Expected results upon completion of the project:

Development of methods and approaches of the theory of few-body systems, settling some still remaining mathematical questions and issues. A contribution to Efimov physics with establishing new universal features in the behavior of ultra-cold few-body systems including the lattice few-body systems. Numerical calculations of ultracold three-atom systems in Efimov or pre-Efimov states by employing Faddeev equations. Theoretical study of non-stationary systems, in particular, the study of few-particle systems in varying external fields. Analysis of bound-state problems and scattering processes in low-dimensional few-particle systems. Development of the dynamical adiabatic theory and theory of hidden crossings of the potential-energy levels. Application of these theories to inelastic transitions in atom-atom collisions.

Expected results of the project in the current year:
Investigation of cluster features of light weakly bound nuclei at different collision energies.

Study of bound states and scattering processes in two- and three-atomic systems of rare gases.

Develpoment of a method for determining the field-free molecular orientation by two-color shaped laser pulses.

Investigation of multi-component few-body systems in the low-energy limit.

Investigation of acceleration and ionization of neutral atoms by electromagnetic pulses.

Extension of the a priori tan Θ theorem for spectral subspace of a self-adjoint Hamiltonian to unitary invariant norms.

Investigation of the influence of characteristics of colliding beams of photons and relativistic electrons on the magnitude of the differential and total cross sections for inverse Compton scattering.

Study of weakly bound states of a quantum particle moving in two-dimensional space.

Development of a method for calculation of extremely narrow resonances in binary collisions of quantum systems. 

Investigation of canalized states in thin films. 

Time-dependent analysis of the Coulomb and nuclear breakup reaction of halo nuclei on a light target.

Brief annotation and scientific rationale:

The aim of the project is to study the universal laws in relativistic collisions of heavy ions accompanied by various particles production; determination of the most important observables to test the equation of state of the nucleus; theoretical support for experiments at the NICA complex. The large nuclear transparency compared to the predictions of Glauber-like models may indicate the presence of color transparency and should be carefully considered. Based on the generalized eikonal approximation, nuclear transparencies in dd collisions will be calculated, which are available at NICA SPD. It is planned to study three/four-nucleon bound (³He,T,⁴He) and scattering systems (elastic proton-deuteron) in the Bethe-Salpeter-Faddeev relativistic formalism. Study the properties of heated and compressed nuclear matter in the collision of heavy ions is based on the Nambu-Iona-Lasinio Polyakov loop model.

Our theoretical efforts are aimed at solving the following problems:

– improving transport approaches for describing the dynamics of relativistic collisions of heavy ions;

– identification of the most important observables in relativistic collisions of heavy ions to test the equation of state of the nucleus;

– study of the time of evolution of rapidly colliding systems to a local isotropic state in momentum space;

– study of the features of the interaction of high-energy gamma quanta with a strong laser field;

– consideration of relativistic effects in low-nucleon systems.

Expected results upon completion of the project:

Development of theoretical models and methods in the theory of nonlinear quantum processes of interaction of charged particles with intense electromagnetic fields. In this case, in addition to the dependence of observables on the field intensity, it is planned to study the polarization effects and the role of the shape and the carrier phase of the pulse.

Extension of the relativistic consideration of three-nucleon (³He,T) systems in the formalism of the Bethe-Salpeter-Faddeev equation with separable interaction to four-nucleon systems in the Yakubovsky formalism (calculation of the ⁴He binding energy, electromagnetic form factor of the system). Investigation of elastic proton-deuteron backscattering using the relativistic three-nucleon Bethe-Salpeter-Faddeev equation with a separable interaction kernel (taking into account nucleon rescattering diagrams). Consideration of the elastic electromagnetic form factor of the pion taking into account the anomalous magnetic moment of the quark in the framework of the covariant separable quark-quark interaction.

Study of the properties of heated and compressed nuclear matter in the collision of heavy ions. Of particular interest is the study of possible phase transitions that occur during the cooling of the system, as well as the problem of violation of CP invariance in strong interactions, which may be a consequence of the influence of the chiral anomaly on the topological structure of QCD vacuum in strong magnetic fields arising during the collision of heavy ions. The purpose of the study is to consider how the scattering cross section changes depending on the properties of the medium. Study of two-photon and Dalitz decays of light mesons within the NJL model at finite temperature and density. The production spectrum of dilepton pairs is directly related to various intermediate states of quark-hadron matter, and its study can provide information on phase transitions. 

Investigations of the phenomenon of color transparency (CT), short-range nucleon-nucleon correlations and cumulative effect. Predictions for planned CPU search experiments at FAIR PANDA and NICA SPD. Based on the generalized eikonal approximation, taking into account the CT effects, we will calculate the nuclear transparency in the hard processes d(d,2p)nn and A(p,2p) with heavier nuclear targets ( A >2) , for which the CT effects should be stronger. 

Development of a solid theoretical basis for describing the interaction of a proton with a SRC pair in the nucleus, taking into account the NLS/VKD. Nucleon-nucleon short-range correlations (SRC) manifest themselves in interactions of high-energy particles with nuclei with sufficiently large momentum transfers (Q > 1 GeV). 

Investigation of the influence of the nuclear medium on such fundamental characteristics of the elementary NN amplitude as the total cross section for scattering of a nucleon by a bound nucleon of the nuclear medium, the energy dependence of the ratio of its real part to the imaginary part, as well as its slope parameter depending on the momentum transferred to the nucleon bound in the nucleus.

Calculation of exact hadronic distributions in transverse momentum and rapidity by new methods within the framework of
Tsallis-1, Tsallis-3 and q-dual statistics and their application to describe experimental data for hadrons produced in collisions of heavy ions and protons with protons at LHC, RHIC, NICA and FAIR energies. Generalization of the quantum-statistical hadron model with exactly conserved strangeness of the system to the case of exact conservation of the baryon and electric charges of the system and finding recursive equations for the exact solution of the partition function and ensemble averages. The use of this model to calculate the multiplicity of identified hadrons produced in heavy ion collisions at LHC, RHIC, NICA and FAIR energies. 

Investigations of the behavior of ghost and gluon propagators at finite temperature in an approach based on the Dyson-Schwinger equation in the Landau gauge in the truncated rainbow approximation. It is planned to investigate possible phase transitions from a bound state of a glueball to a free gluon plasma for the problem of phase transitions to a quark-gluon plasma in a hot nuclear medium (in processes in experiments at the NICA facility).

Expected results of the project in the current year:

Study of polarization observables in nonlinear Compton scattering in the interaction of ultra-relativistic electrons with polarized intense laser pulses. Calculations related to the development of large laser centers in JINR member countries. 

Construction of a relativistic approach for studying four-particle systems at high energies based on the Bethe-Salpeter and Faddeev-Yakubovsky equations and its application to the study of the ⁴He nucleus, in particular, calculation of its binding energy and state amplitudes. 

Study of the dependence of Y-meson cross sections in BB collisions on the properties of the medium in the framework of the covariant quark model with the SU(5) Lagrangian with anomalous interactions. 

Calculation of nuclear transparency in the hard process d(d,2p)nn based on the generalized eikonal approximation taking into account the effects of color transparency. 

Analysis of proton-nucleus scattering data at energies of 100-1000 MeV in order to reveal the elementary amplitude of proton scattering on a bound nucleon of the nucleus. 

Formulation of the local equilibrium statistical model with flows for the relativistic hadrons in the Boltzmann-Gibbs and Tsallis statistics to describe the transverse momentum distributions of hadrons created in proton-proton and heavy-ion collisions at high energies.

Study of possible phase transitions from a bound state of a glueball to a free gluon plasma.