The description of nuclei starting from the constituent nucleons and the realistic interactions among them has been a long-standing goal in nuclear physics. In addition to the complex nature of the nuclear forces, with two-, three- and possibly higher many-nucleon components, one faces the quantum-mechanical many-nucleon problem governed by an interplay between bound and continuum states. In recent years, significant progress has been made in ab initio nuclear structure and reaction calculations based on input from QCD-employing Hamiltonians constructed within chiral effective field theory. After a brief overview of the field, we focus on ab initio many-body approaches—built upon the no-core shell model—that are capable of simultaneously describing both bound and scattering nuclear states, and present results for resonances in light nuclei, reactions important for astrophysics and fusion research. In particular, we review recent calculations of resonances in the ⁶ He halo nucleus, of five- and six-nucleon scattering, and an investigation of the role of chiral three-nucleon interactions in the structure of ⁹ Be. Further, we discuss applications to the ⁷ Be ( p , γ ) 8 B radiative capture. Finally, we highlight our efforts to describe transfer reactions including the ³ H ( d , n ) 4 He fusion.

The weakly bound exotic ${}^{11}\mathrm{Be}$ nucleus, famous for its ground-state parity inversion and distinct $n+{}^{10}\mathrm{Be}$ halo structure, is investigated from first principles using chiral two- and three-nucleon forces. An explicit treatment of continuum effects is found to be indispensable. We study the sensitivity of the ${}^{11}\mathrm{Be}$ spectrum to the details of the three-nucleon force and demonstrate that only certain chiral interactions are capable of reproducing the parity inversion. With such interactions, the extremely large $E1$ transition between the bound states is reproduced. We compare our photodisintegration calculations to conflicting experimental data and predict a distinct dip around the $3/2_1^{-}$ resonance energy. Finally, we predict low-lying $3/2^{+}$ and $9/2^{+}$ resonances that are not or not sufficiently measured in experiments.

International audienceThe 3He(α,γα,γ)7Be and 3H(α,γα,γ)7Li astrophysical S factors are calculated within the no-core shell model with continuum using a renormalized chiral nucleon–nucleon interaction. The 3He(α,γα,γ)7Be astrophysical S factors agree reasonably well with the experimental data while the 3H(α,γα,γ)7Li ones are overestimated. The seven-nucleon bound and resonance states and the α + 3He/3H elastic scattering are also studied and compared with experiment. The low-lying resonance properties are rather well reproduced by our approach. At low energies, the s-wave phase shift, which is non-resonant, is overestimated

The fusion of deuterium (D) with tritium (T) is the most promising of the reactions that could power thermonuclear reactors of the future. It may lead to even more efficient energy generation if obtained in a polarized state, that is with the spin of the reactants aligned. Here, we report first-principles predictions of the polarized DT fusion using nuclear forces from effective field theory. By employing the ab initio no-core shell model with continuum reaction method to solve the quantum mechanical five-nucleon problem, we accurately determine the enhanced fusion rate and angular distribution of the emitted neutron and ⁴He. Our calculations demonstrate in detail the small contribution of anisotropies, placing on a firmer footing the understanding of the rate of DT fusion in a polarized plasma. In the future, analogous calculations could be used to obtain accurate values for other, more uncertain thermonuclear reaction data critical to nuclear science applications.

We provide a unified ab initio description of the ${}^6\mathrm{Li}$ ground state and elastic scattering of deuterium ($d$) on ${}^4\mathrm{He}$ ($\alpha$) using two- and three-nucleon forces from chiral effective field theory. We analyze the influence of the three-nucleon force and reveal the role of continuum degrees of freedom in shaping the low-lying spectrum of ${}^6\mathrm{Li}$. The calculation reproduces the empirical binding energy of ${}^6\mathrm{Li}$, yielding an asymptotic $D$- to $S$-state ratio of the ${}^6\mathrm{Li}$ wave function in the $d+\alpha$ configuration of $-0.027$, in agreement with a determination from ${}^6\mathrm{Li}\text{−}{}^4\mathrm{He}$ elastic scattering, but overestimates the excitation energy of the $3^{+}$ state by 350 keV. The bulk of the computed differential cross section is in good agreement with data. These results endorse the application of the present approach to the evaluation of the ${}^2\mathrm{H}(\alpha ,\gamma ){}^6\mathrm{Li}$ radiative capture, responsible for the big-bang nucleosynthesis of ${}^6\mathrm{Li}$.

We extend the ab initio no-core shell model/resonating-group method to include three-nucleon ($3N$) interactions for the description of nucleon-nucleus collisions. We outline the formalism, give algebraic expressions for the $3N$-force integration kernels, and discuss computational aspects of two alternative implementations. The extended theoretical framework is then applied to nucleon-${}^{4}$He elastic scattering using similarity-renormalization-group (SRG)-evolved nucleon-nucleon plus $3N$ potentials derived from chiral effective field theory. We analyze the convergence properties of the calculated phase shifts and explore their dependence upon the SRG evolution parameter. We include up to six excited states of the ${}^{4}\text{He}$ target and find significant effects from the inclusion of the chiral $3N$ force, e.g., it enhances the spin-orbit splitting between the $3/{2}^{$-${}}$and $1/{2}^{$-${}}$ resonances and leads to an improved agreement with the phase shifts obtained from an accurate $R$-matrix analysis of the five-nucleon experimental data. We find remarkably good agreement with measured differential cross sections at various energies below the $d$-${}^{3}$H threshold, while analyzing powers manifest larger deviations from experiment for certain energies and angles.