Chiral Effective Field Theory Potentials Research Articles

Benchmark calculations of pure neutron matter with realistic nucleon-nucleon interactions

We report benchmark calculations of the energy per particle of pure neutron matter as a function of the baryon density using three independent many-body methods: Brueckner-Bethe-Goldstone, Fermi hypernetted chain/single-operator chain, and auxiliary-field diffusion Monte Carlo. Significant technical improvements are implemented in the latter two methods. The calculations are made for two distinct families of realistic coordinate-space nucleon-nucleon potentials fit to scattering data, including the standard Argonne $v_{18}$ interaction and two of its simplified versions, and four of the new Norfolk $\Delta$-full chiral effective field theory potentials. The results up to twice nuclear matter saturation density show some divergence among the methods, but improved agreement compared to earlier work. We find that the potentials fit to higher-energy nucleon-nucleon scattering data exhibit a much smaller spread of energies.

Experimental identification of the T=1 , Jπ=6+ state of Co54 and isospin symmetry in A=54 studied via one-nucleon knockout reactions

New experimental data obtained from $\gamma$-ray tagged one-neutron and one-proton knockout from $^{55}$Co is presented. A candidate for the sought-after $T=1, T_z = 0, J^{\pi} = 6^+$ state in $^{54}$Co is proposed based on a comparison to the new data on $^{54}$Fe, the corresponding observables predicted by large-scale-shell-model (LSSM) calculations in the full $fp$-model space employing charge-dependent contributions, and isospin-symmetry arguments. Furthermore, possible isospin-symmetry breaking in the $A=54$, $T=1$ triplet is studied by calculating the experimental $c$ coefficients of the isobaric mass multiplet equation (IMME) up to the maximum possible spin $J=6$ expected for the $(1f_{7/2})^{-2}$ two-hole configuration relative to the doubly-magic nucleus $^{56}$Ni. The experimental quantities are compared to the theoretically predicted $c$ coefficients from LSSM calculations using two-body matrix elements obtained from a realistic chiral effective field theory potential at next-to-next-to-next-to-leading order (N$^3$LO).

Erratum: Nuclear and neutron matter G -matrix calculations with a chiral effective field theory potential including effects of three-nucleon interactions [Phys. Rev. C 88 , 064005 (2013)

Erratum: Nuclear and neutron matter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>G</mml:mi></mml:math> -matrix calculations with a chiral effective field theory potential including effects of three-nucleon interactions [Phys. Rev. C <b>88</b> , 064005 (2013)

How Many-Body Correlations andαClustering ShapeHe6

The Borromean $^6$He nucleus is an exotic system characterized by two `halo' neutrons orbiting around a compact $^4$He (or $\alpha$) core, in which the binary subsystems are unbound. The simultaneous reproduction of its small binding energy and extended matter and point-proton radii has been a challenge for {\em ab initio} theoretical calculations based on traditional bound-state methods. Using soft nucleon-nucleon interactions based on chiral effective field theory potentials, we show that supplementing the model space with $^4$He+$n$+$n$ cluster degrees of freedom largely solves this issue. We analyze the role played by the $\alpha$-clustering and many-body correlations, and study the dependence of the energy spectrum on the resolution scale of the interaction.

Nuclear and neutron matterG-matrix calculations with a chiral effective field theory potential including effects of three-nucleon interactions

The energies of symmetric nuclear matter and neutron matter are evaluated in the lowest-order Brueckner theory using a chiral effective field theory potential including effects of a three-nucleon force (3NF). The 3NF is first reduced to a density-dependent nucleon-nucleon ($NN$) force by folding with single-nucleon degrees of freedom in infinite matter. Adding the reduced $NN$ force to the initial $NN$ force and applying a partial-wave expansion, $G$-matrix calculations are performed in pure neutron matter as well as in symmetric nuclear matter. A saturation curve which is close to the empirical one is obtained. It is explicitly shown that the cutoff-energy dependence of the calculated energies is substantially reduced by including the 3NF. Characteristics of 3NF contributions in separate spin and isospin channels are discussed. Calculated energies of neutron matter are very similar to those employed in the literature for considering neutron star properties.

Matter and charge radius of6He in the hyperspherical-harmonics approach

We present ab-initio calculations of the binding energy and radii of the two-neutron halo nucleus 6He using two-body low-momentum interactions based on chiral effective field theory potentials. Calculations are performed via a hyperspherical harmonics expansion where the convergence is sped up introducing an effective interaction for non-local potentials. The latter is essential to reach a satisfactory convergence of the extended matter radius and of the point-proton radius. The dependence of the results on the resolution scale is studied. A correlation is found between the radii and the two-neutron separation energy. The importance of three-nucleon forces is pointed out comparing our results and previous calculations to experiment.

Improved nuclear matter calculations from chiral low-momentum interactions

We present new nuclear matter calculations based on low-momentum interactions derived from chiral effective field theory potentials. The current calculations use an improved treatment of the three-nucleon force contribution that includes a corrected combinatorial factor beyond Hartree-Fock that was omitted in previous nuclear matter calculations. We find realistic saturation properties using parameters fit only to few-body data, but with larger uncertainty estimates from cutoff dependence and the 3NF parametrization than in previous calculations.

Convergence in the no-core shell model with low-momentum two-nucleon interactions

The convergence of no-core shell model (NCSM) calculations using renormalization group evolved low-momentum two-nucleon interactions is studied for light nuclei up to 7Li. Because no additional transformation was used in applying the NCSM framework, the energy calculations satisfy the variational principle for a given Hamiltonian. Dramatic improvements in convergence are found as the cutoffs are lowered. The renormalization group equations are truncated at two-body interactions, so the evolution is only approximately unitary and converged energies for A ⩾ 3 vary with the cutoff. This approximation is systematic, however, and for useful cutoff ranges the energy variation is comparable to natural-size truncation errors inherent from the initial chiral effective field theory potential.