The discovery of the atomic electric dipole moment (EDM) would reveal the simultaneous violation of parity (P) and time-reversal (T) invariance. The EDM can be induced by T-odd forces between the nucleus and atomic electrons. As the nuclear dipole moment is screened according to the Schiff theorem, the appropriate nuclear operator is the Schiff moment that may exist in nuclei under PT-violation. We briefly review the current experimental situation and discuss more in detail the ideas concerning possible collective mechanisms for the enhancement of the nuclear Schiff moment. The most promising directions are related to the coexistence of octupole and quadrupole collective modes, either in the form of static deformation or as soft vibrational excitations. The search for enhancement is important for widening the pool of nuclei as candidates for the atomic EDM as well as for development of nuclear many-body theory beyond standard mean-field and random phase approximations.
The shell model Monte Carlo (SMMC) approach allows for the microscopic calculation of statistical and collective properties of heavy nuclei using the framework of the configuration-interaction shell model in very large model spaces. We present recent applications of the SMMC method to the calculation of state densities and their collective enhancement factors in rare-earth nuclei.
In the stochastic formulation of viscous hydrodynamics, the velocity of a fluid element fluctuates satisfying a similar relation to the quantum-mechanical uncertainty relation. Using a non-relativistic toy model, we show that the presence of such a velocity fluctuation increases the local anisotropy of the momentum distributions of produced hadrons, and thus the collective flow parameters such as $v_2$ is emphasized.
The nuclear shell model assumes an effective mean-field plus interaction Hamiltonian in a specific configuration space. We want to understand how various interaction matrix elements affect the observables, the collectivity in nuclei and the nuclear level density for odd-A and odd-odd nuclei. Using the sd and pf shells, we vary specific groups of matrix elements and study the evolution of energy levels, transition rates and the level density. In all cases studied, a transition between a "normal" and a collective phase is induced, accompanied by an enhancement of the level density in the collect…
For nuclear level densities, a modification of an enhanced generalized superfluid model with different collective state enhancement factors is studied. An effect of collective states on forming the temperature is taken into account. The ready-to-use tables for the asymptotic value of $a$-parameter of level density as well as for addition shift to excitation energy are prepared using the chi-square fit of the theoretical values of neutron resonance spacing and cumulative number of low-energy levels to experimental values. The systematics of these parameters as a function of mass number and neut…
The pre-equilibrium reaction mechanism is considered in the context of the exciton model. A modification to the one-particle one-hole state density is studied which can be interpreted as a collective enhancement. The magnitude of the collective enhancement is set by simulating the Lawrence Livermore National Laboratory (LLNL) pulsed-spheres neutron-leakage spectra. The impact of the collective enhancement is explored in the context of the highly deformed actinide, 239-Pu. A consequence of this enhancement is the removal of fictitious levels in the Distorted-Wave Born Approximation often used i…
We examine the time-reversal-violating nuclear ``Schiff moment'' that induces electric dipole moments in atoms. After presenting a self-contained derivation of the form of the Schiff operator, we show that the distribution of Schiff strength, an important ingredient in the ground-state Schiff moment, is very different from the electric-dipole-strength distribution, with the Schiff moment receiving no strength from the giant dipole resonance in the Goldhaber-Teller model. We then present shell-model calculations in light nuclei that confirm the negligible role of the dipole resonance and show t…
We study the effects of collective flow on charge dependent azimuthal correlations at LHC energies. We propose a series of correlations as a signature of the combined effects of azimuthal collective flow and local charge conservation and perform an analysis within a statistical freeze-out model. We find that present LHC measurements of charge dependent azimuthal correlations are consistent with local charge conservation on the kinetic freeze-out surface. In view of experimental searches for signatures of the chiral-magnetic effect, we provide an alternative explanation of the charge dependence…
A microscopic method for calculating nuclear level densities (NLD) is developed, based on the framework of energy density functionals. Intrinsic level densities are computed from single-quasiparticle spectra obtained in a finite-temperature self-consistent mean-field (SCMF) calculation that takes into account nuclear deformation, and is specified by the choice of the energy density functional (EDF) and pairing interaction. The total level density is calculated by convoluting the intrinsic density with the corresponding collective level density, determined by the eigenstates of a five-dimension…
The enhancements of CP-violating effects in resonance neutron transmissionthrough polarized targets are studied for 2 possible versions of experiment. The importance is stressed of error analysis and of pseudomagnetic effects' compensation.
The advantage of searching for violation of Time Reversal Invariance in neutron induced reactions using relative measurements of Time and Parity violating effects is discussed. This approach gives the enhancement of $T$-violating effects by many orders of magnitude and, at the same time, decrees theoretical uncertainties and experimental errors.
Nuclear forces violating parity and time reversal invariance P,T-odd produce P,T-odd nuclear moments, for example, the nuclear Schiff moment. In turn, this moment can induce the electric dipole moment (EDM) in the atom. The contribution to the Schiff moment from the soft collective quadrupole and octupole vibrations in spherical nuclei is calculated in the framework of the quasiparticle random phase approximation with separable quadrupole and octupole forces. The values of nuclear Schiff moments predicted for odd 217-221Ra and 217-221Ra isotopes indicate a possibility of enhancement by a facto…
We have carried out a unified microscopic study of electric monopole, quadrupole and magnetic dipole excitations in fast rotating nuclei undergoing backbending, with special attention at the magnetic excitations. We found, among other results, that the strength of the orbital magnetic dipole excitations (scissors mode) gets enhanced by more than a factor four at high rotational frequency, above the backbending region. We provide a physical explanation for such an enhancement.
Octupole deformation results in a strongly enhanced collective Schiff moment in 229Th nucleus. An additional enhancement of time reversal (T) and parity (P) violating effects (such as T,P-violating electric dipole moments) appears in the ground 1Sigma state and in the metastable 3Delta_1 state of diatomic molecule 229ThO. Similar enhancements exist in molecular ions 229ThOH+, 229ThF+ and 225,223RaOH+. Corresponding experiments may be used to test CP-violation theories predicting T,P-violating nuclear forces and to search for axions.
Model independent, $m_1$, adiabatic, $m_{-1}$, and high-energy, $m_3$, energy weighted sums for the isoscalar and isovector nuclear excitations are investigated within the framework of the kinetic theory adopted to the description of a two-component nuclear Fermi-liquid. For both the adiabatic and scaling approaches, the connection of the EWS $m_{-1}$ and $m_3$ to the nuclear stiffness coefficients and the first- and zero-sound velocity is established. We study the enhancement factor $κ_{I}$ in the energy weighted sum $m'_1$ for the isovector excitations and provide the reasonable explanation …
The electric dipole moment (EDM) is a very sensitive probe of CP violation beyond the standard model, and it as been measured in many systems such as atoms, neutrons, etc. The EDM of composite systems may be sensitive to several elementary level CP violating processes, but the theoretical evaluations of the CP violation at different physical (atomic, nuclear, hadronic, elementary) hierarchies are required to unveil them. In this context, we are particularly interested in which CP violating processes are enhanced in a given system, or vice versa. In this proceedings contribution, we will give a…
The nuclear-polarization (NP) energies with the collective model commonly employed in the NP calculations for hydrogenlike heavy ions are found to have serious gauge violations when the ladder and cross diagrams only are taken into account. Using the equivalence of charge-current density with a schematic microscopic model, the NP energy shifts with the collective model are gauge invariantly evaluated for the $1s_{1/2}$ states in $^{208}_{~82}$Pb$^{81+}$ and $^{238}_{~92}$U$^{91+}$.
A fully microscopic model for the description of nuclear level density (NLD) in spherical nuclei is proposed. The model is derived by combining the partition function of the exact pairing solution plus the independent-particle model at finite temperature (EP+IPM) with that obtained by using the collective vibrational states calculated from the self-consistent Hartree-Fock mean field with MSk3 interaction plus the exact pairing and random-phases approximation (SC-HFEPRPA). Two important factors are taken into account in a fully microscopic way, namely the spin cut-off and vibrational enhancemen…
Time reversal invariance violating (TRIV) effects in neutron scattering are very important in a search for new physics, being complementary to neutron and atomic electric dipole moment measurements. In this relation, a sensitivity of TRIV observables to different models of CP-violation and their dependencies on nuclear structure, which can lead to new enhancement factors, are discussed.
We have examined the influence of rotation on the potential energy and the transport coefficients of the collective motion (friction and mass coefficients). For axially symmetric deformation of nucleus Th-224 we have found that at excitations corresponding to temperatures T > 1 MeV the shell correction to the liquid drop energy practically does not depend on the angular rotation. The friction and mass coefficients obtained within the linear response theory for the same nucleus at temperatures larger than T=2 MeV are rather stable with respect to rotation provided that the contributions from sp…
Parity and time invariance violating (${\cal P},{\cal T}$-odd) nuclear forces produce ${\cal P},{\cal T}$-odd nuclear moments, for example, the nuclear Schiff moment. In turn, this moment can induce electric dipole moments (EDMs) in atoms. We estimate the contribution to the Schiff moment from the soft collective octupole vibrations existing in many heavy nuclei. Two possible mechanisms are considered, mixing of the ground state of an odd-$A$ nucleus with the octupole phonon state, and ${\cal P},{\cal T}$-odd admixture to the single-particle wave function of the valence nucleon. We found pract…
The strong interaction effects of isospin- and spin-dependent nucleon-nucleon correlations observed in many-body calculations are interpreted in terms of a one-pion exchange mechanism. Including such effects in computations of nuclear parity violating effects leads to enhancements of about 10%. A larger effect arises from the one-boson exchange nature of the parity non-conserving nucleon- nucleon interaction, which depends on both weak and strong meson-nucleon coupling constants. Using values of the latter that are constrained by nucleon-nucleon phase shifts leads to enhancements of parity vio…
Time Reversal Invariant Violating (TRIV) effects in neutron transmission through a nuclei target are discussed. We demonstrate the existence of a class of experiments that are free from falls asymmetries. We discuss enhancement of TRIV effects. We analyze a model experiment and show that such tests have a discovery potential of $10^2 - 10^4$ compare to current limits.
The basic parameters for calculations of radiative neutron capture , photon strength functions and nuclear level densities near the neutron separation energy are determined based on experimental data without an ad-hoc assumption about axial symmetry - at variance to previous analysis. Surprisingly few global fit parameters are needed in addition to information on nuclear deformation, taken from Hartree Fock Bogolyubov (HFB) calculations with the Gogny force, and the generator coordinator method (GCM) assures properly defined angular momentum. For a large number of nuclei the GDR shapes and the…
We present the microscopic model for collective effects, built on string-string interactions (string shoving and rope hadronization), recently implemented in the PYTHIA 8 and DIPSY event generators. Rope hadronization is shown to give a good description of strangeness enhancement across pp, pA and AA collisions systems, while string shoving qualitatively describes the ridge observed in pp collisions.
Parity and time invariance violating forces produce collective P- and T- odd moments in nuclei with static octupole deformation. Collective Schiff moment, electric octupole and dipole and also magnetic quadrupole appear due to the mixing of rotational levels of opposite parity and can exceed single-particle moments by more than a factor of 100. This enhancement is due to two factors, the collective nature of the intrinsic moments and the small energy separation between members of parity doublets. The above moments induce T- and P- odd effects in atoms and molecules. Experiments with such syste…
