Properties of finite nuclei are evaluated with two-nucleon (NN) and three-nucleon (NNN) interactions derived within chiral effective field theory. The nuclear Hamiltonian is fixed by properties of the A=2 system, except for two low-energy constants (LECs) that parametrize the short range NNN interaction, which we constrain with the A=3 binding energies. We investigate the sensitivity of 4He, 6Li, 10,11B, and 12,13C properties to the variation of the constrained LECs. We identify observables that are sensitive to this variation and find preferred values that give the best overall description. We demonstrate that the NNN interaction terms significantly improve the binding energies and spectra of mid-p-shell nuclei not just with the preferred choice of the LECs but even within a wide range of the constrained LECs. We find that a very high quality description of these nuclei requires further improvements to the chiral Hamiltonian.

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We present in detail a formulation of the shell model as a path integral and Monte Carlo techniques for its evaluation. The formulation, which linearizes the two-body interaction by an auxiliary field, is quite general, both in the form of the effective `one-body' Hamiltonian and in the choice of ensemble. In particular, we derive formulas for the use of general (beyond monopole) pairing operators, as well as a novel extraction of the canonical (fixed-particle number) ensemble via an activity expansion. We discuss the advantages and disadvantages of the various formulations and ensembles and give several illustrative examples. We also discuss and illustrate calculation of the imaginary-time response function and the extraction, by maximum entropy methods, of the corresponding strength function. Finally, we discuss the "sign-problem" generic to fermion Monte Carlo calculations, and prove that a wide class of interactions are free of this limitation.Comment: 38 pages, RevTeX v3.0, figures available upon request; Caltech Preprint #MAP-15

We present a practical solution to the "sign problem" in the auxiliary field Monte Carlo approach to the nuclear shell model. The method is based on extrapolation from a continuous family of problem-free Hamiltonians. To demonstrate the resultant ability to treat large shell-model problems, we present results for 54 Fe in the full f p-shell basis using the Brown-Richter interaction. We find the Gamow-Teller β + strength to be quenched by 58% relative to the single-particle estimate, in better agreement with experiment than previous estimates based on truncated bases.

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Isospin-mixing corrections for superallowed Fermi transitions in fp-shell nuclei are computed within the framework of the shell model. The study includes three nuclei that are part of the set of nine accurately measured transitions as well as five cases that are expected to be measured in the future at radioactivebeam facilities. We also include some new calculations for 10 C. With the isospin-mixing corrections applied to the nine accurately measured f t values, the conserved-vector-current hypothesis and the unitarity condition of the Cabbibo-Kobayashi-Maskawa (CKM) matrix are tested.

We report the microscopic origins of the anomalously suppressed beta decay of 14 C to 14 N using the ab initio no-core shell model (NCSM) with the Hamiltonian from chiral effective field theory (EFT) including three-nucleon force (3NF) terms. The 3NF induces unexpectedly large cancellations within the p-shell between contributions to beta decay, which reduce the traditionally large contributions from the NN interactions by an order of magnitude, leading to the long lifetime of 14 C. The measured lifetime of 14 C, 5730±30 years, is a valuable chronometer for many practical applications ranging from archeology to physiology. It is anomalously long compared to lifetimes of other light nuclei undergoing the same decay process, allowed Gamow-Teller (GT) betadecay, and it poses a major challenge to theory since traditional realistic nucleon-nucleon (NN) interactions alone appear insufficient to produce the effect [1]. Since the transition operator, in leading approximation, depends on the nucleon spin and isospin but not the spatial coordinate, this decay provides a precision tool to inspect selected features of the initial and final states. To convincingly explain this strongly inhibited transition, we need a microscopic description that introduces all physicallyrelevant 14-nucleon configurations in the initial and final states and a realistic Hamiltonian that governs the configuration mixing.We report the first no-core solutions of 14 C and 14 N using a Hamiltonian with firm ties to the underlying theory of the strong interaction, Quantum Chromodynamics (QCD), which allows us to isolate the key canceling contributions involved in this beta decay. We find that the three-nucleon force (3NF) of chiral perturbation theory (ChPT) plays a major role in producing a transition rate that is near zero, needed for the anomalous long lifetime. A chiral 3NF with coupling constants consistent with other works and within their natural range can provide the precise lifetime. This indicates that corrections to the lifetime that arise from increasing the basis space, from including additional many-body interactions and from corrections to the GT operator in ChPT [2] may be absorbed into an allowed choice of the 3NF.Our work features two major advances over recent alternative explanations [3,4]: (1) we treat all nucleons on the same dynamical footing with the no-core shell model (NCSM) [5], and (2) we include the 3NF of ChPT [6] as a full 3-nucleon interaction. This follows previous work detailing the structure and electroweak properties of selected A=10-13 nuclei [7] with the same chiral NN + 3NF. We also establish a foundation for future work on the GT transitions to excited A=14 states [8].ChPT provides a theoretical framework for internucleon interactions based on the underlying symmetries of QCD. Beginning with pionic or the nucleon-pion system [9] one works consistently with systems of increasing nucleon number [10][11][12]. One makes use of the explicit and spontaneous breaking of chiral symmetry to expand the strong interactio...

The Similarity Renormalization Group (SRG) is used to soften interactions for ab initio nuclear structure calculations by decoupling low-and high-energy Hamiltonian matrix elements. The substantial contribution of both initial and SRG-induced three-nucleon forces requires their consistent evolution in a three-particle basis space before applying them to larger nuclei. While in principle the evolved Hamiltonians are unitarily equivalent, in practice the need for basis truncation introduces deviations, which must be monitored. Here we present benchmark no-core full configuration calculations with SRG-evolved interactions in p-shell nuclei over a wide range of softening. These calculations are used to assess convergence properties, extrapolation techniques, and the dependence of energies, including four-body contributions, on the SRG resolution scale.