Facility for Rare Isotope Beams

I discuss recent developments in "ab initio" calculations for light nuclei using basis function expansion methods. In principle any nuclear potential can be used as input for such calculations, though numerical convergence depends on the softness of the potential. Renormalizations techniques, such as Lee-Suzukl, and similarity group transformations have been used to improve convergence. I present results for chiral effective two-nucleon and three-nucleon potentials and for a phenomenological two-body potential (JISP16), which both give a good description of a range of properties of nuclei in the A = 6 to 16 range. I also present initial results for neutron droplets in an external field.

The equation of state and pairing gap of neutron matter at low densities are important to the structure and cooling of neutron stars, and potentially to the surface properties of neutron-rich nuclei. Cold fermionic gases provide another setting with quite similar physics. Both these systems are strongly paired, i.e the pairing gap is of the order of the Fermi energy. Several many-body schemes have been devised in an attempt to accurately describe the strong coupling regime. In this talk, I will discuss recent results on the equation of state, the pairing gap, and other observables that we have calculated using a microscopic ab initio method. I will also mention some even more recent results on Fermi-Fermi mixtures.

I will discuss equation of state and spin-isospin correlations of hot and dense nucleonic matter found in supernovae and proto-neutron stars. The calculations are done using an ab initio variational many body technique, where the only inputs are the two nucleon and three nucleon interactions in free space. Recently, we showed how a variational theory can be constructed for a system of fermions at finite temperature, which can fully exploit the powerful chain summation techniques developed for theories at zero temperature. I will present results using this method and discuss the consequences for the fate of neutral pion condensation at finite temperature.

This talk discusses the development and applications of theoretical and computational methods to study three-body processes in the framework of my Ph.D thesis. The main focus is on the calculation of three-body resonances and bound states. We introduce a novel approach that calculates three-body bound states and resonances. I will discuss Efimov states and resonances, three-body shape resonances, three-body Feshbach resonances, three-body predissociated states in systems with a conical intersection, and the calculation of three-body recombination rate coefficients. The method was applied to model systems and realistic systems. The developed approach is quite general and can be applied to problems in nuclear, atomic, molecular, and astrophysics.

I discuss current efforts to extract hadronic interaction parameters from LQCD, enumerating current difficulties placed by available computer resources and algorithm limitations. I will also talk about future possibilities coming from (soon to come) increased computer resources and algorithm development. Finally, I will discuss the role that national labs, and in particular Lawrence Livermore National Lab, can and should play in the area of LQCD.

The talk consists of two parts, neutron-proton pairing and nuclear Schiff moment: (i) In the theory of nuclear pair correlations, each Cooper pair contains two neutrons or two protons. It also can contain on neutron and one proton. Neutron-proton (NP) pairing can be important in N-Z nuclei, where neutrons and protons occupy the same spatial orbitals and have the maximal spatial ovrrlap. I will discuss the self-consistent calculation of T=1 and T=0 np pairing in N-Z nuclei. (ii) Time-reversal violation (or CP violation) plays an important role in the early universe, causing excess of matter over antimatter. CP violation from Standard Model (SM) is not strong enough to produce the current asymmetry between matter and antimatter. It is believed that there are other sources for T violation originating from physics beyond SM. The electric dipole moment (EDM) of the electron, neutron, and atoms is a direct evidence for T violation. Because atomic EDM is screened by its electrons, the residual EDM is caused by the "Schiff Operator". In theoretical studies, one calculates the nuclear Schiff moment instead of the EDM. I will discuss the self-consistent calculation of nuclear Schiff moments.

The search for a non-zero electric dipole moment of the neutron (nEDM) has been central to constraining the new sources of CP-violation naturally found in many extensions of the Standard Model. The development of new technologies has improved the experimental sensitivity by eight orders of magnitude over the last six decades. At present, the best limit of 2.9x10^-26 e cm was achieved at the Institut Laue-Langevin (ILL) using ultra-cold neutrons (UCNs) in a magnetic trap. A new experiment with the goal to improve the present value by two orders of magnitude is under construction at the Spallation Neutron Source (SNS, ORNL). A high flux of polarized cold neutrons will be converted to UCNs in a superfluid helium-4 target. Trace amounts of polarized ³He atoms will be injected into the target as well. The ³He nuclei will serve as a co-magnetometer in a very homogeneous DC magnetic field, and the strong spin dependence in the n(³He,p)t reaction will be exploited to determine the sensitivity of the neutron spin precession in external electric fields. The present status of the experiment and the technology to achieve this objective will be described.

Three-body scattering is described in the framework of exact Faddeev-type integral equations that are solved numerically using momentum-space partial-wave basis. The Coulomb interaction between charged particles is included using the screening and renormalization method. The technique is applied to three-nucleon scattering and to elastic, transfer, and breakup reactions in three-body-like nuclear systems. Examples are deuteron scattering on stable nuclei ⁴He, ¹⁰Be, ¹²C, ¹⁴C, ¹⁶O, ⁴⁰Ca, and ⁵⁸Ni and proton scattering on weakly bound two-body systems such as ¹¹Be, ¹³C, ¹⁵C, and ¹⁷O. These calculations allow us to evaluate the accuracy of traditional approximate nuclear reaction approaches like the continuum-discretized coupled-channels (CDCC) method but also to test novel dynamical models such as nonlocal optical potentials. Finally, the technique is extended to low-energy four-nucleon elastic and transfer reactions.

Applying a variational multiparticle-multihole configuratoin mixing method whose purpose is to include correlations beyond the mean field in a unified way without particle number and Pauli principle violations, we investigate pairing-like correlations in the ground states of ¹¹⁶Sn, ¹⁰⁶Sn and ¹⁰⁰Sn. The same effective nucleon-nucleon interaction namely, the DIS parameterization of the Gogny force is used to derive both the mean field and correlation components of nuclear wave functions. Calculations are performed using an axial symmetry representation. The structure of correlated wave functions, their convergence with respect to the number of particle-hole excitations and the influence of correlations on single-particle level spectra and occupation probabilities are analyzed and compared with results obtained with the same two-body effective interaction from BCS, Hartree-Fock-Bogoliubov and particle number projected after variation BCS approaches. Calculations of nuclear radii and the first theoretical excited 0⁺ states are compared with experimental data.

Using an energy-independent non-Hermitian Hamiltonian approach to open systems, we fully describe transport through a sequence of potential barriers as external barriers are varied. Analyzing the complex eigenvalues of the non-Hermitian Hamiltonian model, a transition to a superradiant regime is shown to occur. Transport properties undergo a strong change at the superradiance transition, specifically a drastic change in the structure of resonances is demonstrated. Our analysis is extended to the case of multidimensional systems.

At the present, Skyrme-type of energy density functionals (EDF), with many different parametrizations, are the most widely used functionals in the nuclear physics. Skyrme functional, however, can not describe all the nuclear properties with desired accuracy. In my talk I will discuss next generation EDFs which go beyond Skyrme. Also, I will discuss strategies to to fit the functional parameters.

Compton scattering on light nuclei (A=2,3) has emerged as an effective avenue to search for signatures of neutron polarizabilities, both spin-independent and spin-dependent ones. In this discussion, I will focus on the theoretical aspect of Compton scattering on light nuclei; giving first a brief overview and thereafter concentrating on our Compton scattering calculations based on Chiral effective theory of energies of the order of pion mass. These elastic gamma-d and gamma-He^-3 calculations include nucleons, pions as the basic degrees of freedom. I will also discuss gamma-d results where the Delta-isobar has been included explicitly. Our results on unpolarized and polarization observables suggests that a combination of experiments and further theoretical efforts will provide an extraction of the neutron polarizabilities.