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We present a semi-microscopic study of the 16C(d,p)17C transfer reaction. The 17C overlap integrals and spectroscopic factors are obtained from a microscopic cluster model, involving many 16C+n configurations. This microscopic model provides a fair description of the 17C bound-state energies. The 16C+d scattering wave functions are defined in the CDCC method, where the deuteron breakup is simulated by pseudostates. The transfer cross sections are in good agreement with recent data. We confirm the 16C(2+)+n structure of the ground state, and show that deuteron breakup effects have a significant influence on the cross sections. We study the 17C(p,d)16C reverse reaction and suggest that the cross section to the 2+ state should be large. A measurement of the ground-state cross section would provide a strong test of the microscopic wave functions., Comment: 8 pages, 5 figures, accepted for publication in Phys. Rev. C

Given the established 2 alpha structure of 8Be, a realistic model of 4 interacting alpha clusters must be used to obtain a 8Be+8Be interaction potential. Such a four-body problem poses a challenge for the determination of the 8Be+8Be optical potential (OP) that is still unknown due to the lack of the elastic 8Be+8Be scattering data. The main goal of the present study is to probe the complex 8Be+8Be optical potential in the coupled reaction channel (CRC) study of the alpha transfer 12C(alpha,8Be) reaction measured at 65 MeV, and to obtain the spectroscopic information on the alpha+8Be cluster configuration of 12C. The 3- and 4-body Continuum-Discretized Coupled Channel (CDCC) methods are used to calculate the elastic alpha+8Be and 8Be+8Be scattering at the energy around 16 MeV/nucleon, with the breakup effect taken into account explicitly. Using the CDCC-based OP and alpha spectroscopic factors given by the cluster model calculation, a good CRC description of the alpha transfer data without any adjustment of the (complex) potential strength., Comment: Phys. Rev. C {\bf 102}, 024622 (2020)

The 11Li + p and 11Li + d reactions are investigated in the Continuum Discretized Coupled Channel (CDCC) method with a three-body description (9Li + n + n) of 11Li. I first discuss the properties of 11Li, and focus on E1 transition probabilities to the continuum. The existence of a 1- resonance at low excitation energies is confirmed, but the associated E1 transition from the ground state does not have an isoscalar character, as suggested in a recent experiment. In a second step, I study the 11Li + p elastic cross section at Elab = 66 MeV in the CDCC framework. I obtain a fair agreement with experiment, and show that breakup effects are maximal at large angles. The breakup cross section is shown to be dominated by the 1- dipole state in 11Li, but the role of this resonance is minor in elastic scattering. From CDCC equivalent 11Li + p and 11Li + n potentials, I explore the 11Li + d cross section within a standard three-body 11Li +(p + n) model. At small angles, the experimental cross section is close to the Rutherford scattering cross section, which is not supported by the CDCC. A five-body (9Li+n+n)+(p+n) is then performed. Including breakup states in 11Li and in the deuteron represents a numerical challenge for theory, owing to the large number of channels. Although a full convergence could not be reached, the CDCC model tends to overestimate the data at small angles. I suggest that measurements of the 9Li + p elastic scattering would be helpful to determine more accurate optical potentials. The current disagreement between experiment and theory on 11Li + d scattering also deserves new experiments at other energies., Comment: 12 pages, 10 figures, accepted at Phys. Rev. C

The Lagrange-mesh $R$-matrix method is generalized to inhomogeneous equations. This method is numerically stable and efficient. It can be directly used for transfer reactions with the formalism discussed by Ascuitto and Glendenning [Phys. Rev. 181,1396 (1969)] and for inclusive breakup reactions modeled by Ichimura, Austern, and Vincent [Phys. Rev. C 32, 431 (1985)]. We first present a simple example to assess the method. Then the application to the $^{93}$Nb($d$,$pX$) non-elastic breakup is discussed., Comment: 7 pages, 6 figures

We use a microscopic multicluster model to investigate the structure of $^{10}$Be and of $^{11}$Be. These nuclei are described by $\alpha+\alpha+n+n$ and $\alpha+\alpha+n+n+n$ configurations, respectively, within the Generator Coordinate Method (GCM). The 4- and 5-body models raise the problem of a large number of generator coordinates (6 for $^{10}$Be and 9 for $^{11}$Be), which requires specific treatment. We address this issue by using the Stochastic Variational Method (SVM), which is based on an optimal choice of the basis functions, generated randomly. The model provides good energy spectra for low-lying states of both nuclei. We also compute rms radii and densities, as well as electromagnetic transition probabilities. We analyze the structure of $^{10}$Be and of $^{11}$Be by considering energy curves, where one of the generator coordinates is fixed during the minimization procedure.

This white paper reports on the discussions of the 2018 Facility for Rare Isotope Beams Theory Alliance (FRIB-TA) topical program "From bound states to the continuum: Connecting bound state calculations with scattering and reaction theory". One of the biggest and most important frontiers in nuclear theory today is to construct better and stronger bridges between bound state calculations and calculations in the continuum, especially scattering and reaction theory, as well as teasing out the influence of the continuum on states near threshold. This is particularly challenging as many-body structure calculations typically use a bound state basis, while reaction calculations more commonly utilize few-body continuum approaches. The many-body bound state and few-body continuum methods use different language and emphasize different properties. To build better foundations for these bridges, we present an overview of several bound state and continuum methods and, where possible, point to current and possible future connections., Comment: 48 pages, 23 figures; paper from the FRIB Theory Alliance Workshop on "From Bound States to the Continuum", June 11-22, 2018

We present a new reaction model, which permits the description of reactions where both colliding nuclei present a low threshold to breakup. The method corresponds to a four-body extension of the Continuum Discretized Coupled Channel (CDCC) model. We first discuss the theoretical formalism, and then apply the method to 11Be+d scattering at Ecm = 45.5 MeV. The 11Be nucleus and the deuteron are described by 10Be+n and p + n structures, respectively. The model involves very large bases, but we show that an accurate description of elastic-scattering data may be achieved only when continuum states of 11Be and of the deuteron are introduced simultaneously. We also discuss breakup calculations, and show that the cross section is larger for 11Be than for the deuteron. The present theory provides reliable wave functions that may be used in the analysis of (d,p) or (d,n) experiments involving radioactive beams., Comment: 5 pages, 4 figures, accepted for publication at Physics Letters B

We use a three-body Continuum Discretized Coupled Channel (CDCC) model to investigate Coulomb and nuclear effects in breakup and reaction cross sections. The breakup of the projectile is simulated by a finite number of square integrable wave functions. First we show that the scattering matrices can be split in a nuclear term, and in a Coulomb term. This decomposition is based on the Lippmann-Schwinger equation, and requires the scattering wave functions. We present two different methods to separate both effects. Then, we apply this separation to breakup and reaction cross sections of 7Li + 208Pb. For breakup, we investigate various aspects, such as the role of the alpha + t continuum, the angular-momentum distribution, and the balance between Coulomb and nuclear effects. We show that there is a large ambiguity in defining the 'Coulomb' and 'nuclear' breakup cross sections, since both techniques, although providing the same total breakup cross sections, strongly differ for the individual components. We suggest a third method which could be efficiently used to address convergence problems at large angular momentum. For reaction cross sections, interference effects are smaller, and the nuclear contribution is dominant above the Coulomb barrier. We also draw attention on different definitions of the reaction cross section which exist in the literature, and which may induce small, but significant, differences in the numerical values., Comment: 12 pages, 11 figures

Primordial or big bang nucleosynthesis (BBN) is one of the three historical strong evidences for the big bang model. Standard BBN is now a parameter free theory, since the baryonic density of the Universe has been deduced with an unprecedented precision from observations of the anisotropies of the cosmic microwave background (CMB) radiation. There is a good agreement between the primordial abundances of 4He, D, 3He and 7Li deduced from observations and from primordial nucleosynthesis calculations. However, the 7Li calculated abundance is significantly higher than the one deduced from spectroscopic observations and remains an open problem. In addition, recent deuterium observations have drastically reduced the uncertainty on D/H, to reach a value of 1.6%. It needs to be matched by BBN predictions whose precision is now limited by thermonuclear reaction rate uncertainties. This is especially important as many attempts to reconcile Li observations with models lead to an increased D prediction. Here, we re-evaluates the D(p,g)3He, D(d,n)3He and D(d,p)3H reaction rates that govern deuterium destruction, incorporating new experimental data and carefully accounting for systematic uncertainties. Contrary to previous evaluations, we use theoretical ab initio models for the energy dependence of the S-factors. As a result, these rates increase at BBN temperatures, leading to a reduced value of D/H = (2.45$\pm0.10)\times10^{-5}$ (2$\sigma$), in agreement with observations., Comment: Submitted to Phys. Rev. D. (without the non-essential Tables IV, IX, X and XI provided here)

We propose alternatives to coupled-channels calculations with loosely-bound exotic nuclei (CDCC), based on the the random matrix (RMT) and the optical background (OPM) models for the statistical theory of nuclear reactions. The coupled channels equations are divided into two sets. The first set, described by the CDCC, and the other set treated with RMT. The resulting theory is a Statistical CDCC (CDCC$_S$), able in principle to take into account many pseudo channels., Comment: 15 pages, 4 figures. Contribution to: "4th International Workshop on Compound-Nuclear Reactions and Related Topics (CNR*13)", October 7-11, 2013, Maresias, Brazil

We investigate the effect of a variation of fundamental constants on primordial element production in Big Bang nucleosynthesis (BBN). We focus on the effect of a possible change in the nucleon-nucleon interaction on nuclear reaction rates involving the A=5 (5Li and 5He) and A=8 (8Be) unstable nuclei. The reaction rates for 3He(d,p)4He and 3H(d,n)4He are dominated by the properties of broad analog resonances in 5Li and 5He compound nuclei respectively. While the triple-alpha process 4He(aa,g)12C is normally not effective in BBN, its rate is very sensitive to the position of the "Hoyle state" and could in principle be drastically affected if 8Be were stable during BBN. We found that the effect of the variation of constants on the 3He(d,p)4He, 3H(d,n)4He nd 4He(aa,g)12C reaction rates is not sufficient to induce a significant effect on BBN, even with a stable 8Be. The main influences come from the weak rates and the A=2, n(p,g)d, bottleneck reaction., Comment: To appear in proceedings of "XII International Symposium on Nuclei in the Cosmos" August 5-12, 2012, Cairns, Australia, PoS(NIC XII)073

We investigate the effect of a variation of fundamental constants on primordial element production in big bang nucleosynthesis (BBN). We focus on the effect of a possible change in the nucleon-nucleon interaction on nuclear reaction rates involving the A=5 (Li-5 and He-5) and A=8 (Be-8) unstable nuclei and complement earlier work on its effect on the binding energy of deuterium. The reaction rates for He3(d,p)He4 and H3(d,n)He4 are dominated by the properties of broad analog resonances in He-5 and Li-5 compound nuclei respectively. While the triple alpha process is normally not effective in BBN, its rate is very sensitive to the position of the "Hoyle state" and could in principle be drastically affected if Be-8 were stable during BBN. The nuclear properties (resonance energies in He-5 and Li-5 nuclei, and the binding energies of Be-8 and D) are all computed in a consistent way using a microscopic cluster model. The n(p,gamma)d, He3(d,p)He4 and H3(d,n)He4 and triple-alpha reaction rates are subsequently calculated as a function of the nucleon-nucleon interaction that can be related to the fundamental constants. We found that the effect of the variation of constants on the He3(d,p)He4 and H3(d,n)He4 and triple-alpha reaction rates is not sufficient to induce a significant effect on BBN, even if Be-8 was stable. In particular, no significant production of carbon by the triple alpha reaction is found when compared to standard BBN. We also update our previous analysis on the effect of a variation of constants on the n(p,gamma)d reaction rate., Comment: 14 pages, 12 figures

A variation of the fundamental constants is expected to affect the thermonuclear rates important for stellar nucleosynthesis. In particular, because of the very small resonant energies of Be8 and C12, the triple $\alpha$ process is extremely sensitive to any such variations. Using a microscopic model for these nuclei, we derive the sensitivity of the Hoyle state to the nucleon-nucleon potential allowing for a change in the magnitude of the nuclear interaction. We follow the evolution of 15 and 60 solar mass, zero metallicity stellar models, up to the end of core helium burning. These stars are assumed to be representative of the first, Population III stars. We derive limits on the variation of the magnitude of the nuclear interaction and model dependent limits on the variation of the fine structure constant based on the calculated oxygen and carbon abundances resulting from helium burning. The requirement that some C12 and O16 be present are the end of the helium burning phase allows for permille limits on the change of the nuclear interaction and limits of order 10^{-5} on the fine structure constant relevant at a cosmological redshift of z ~ 15-20., Comment: 14 pages, 12 figures

We use the R-matrix theory to fit low-energy data on nuclear reactions involved in Big Bang nucleosynthesis. A special attention is paid to the rate uncertainties which are evaluated on statistical grounds. We provide S factors and reaction rates in tabular and graphical formats., Comment: 40 pages, accepted for publication at ADNDT, web site at http://pntpm3.ulb.ac.be/bigbang

From the observations of the anisotropies of the Cosmic Microwave Background (CMB) radiation, the WMAP satellite has provided a determination of the baryonic density of the Universe, \Omega_b.h^2, with an unprecedented precision. This imposes a careful reanalysis of the standard Big-Bang Nucleosynthesis (SBBN) calculations. We have updated our previous calculations using thermonuclear reaction rates provided by a new analysis of experimental nuclear data constrained by $R$-matrix theory. Combining these BBN results with the \Omega_b.h^2 value from WMAP, we deduce the light element (4He, D, 3He and 7Li) primordial abundances and compare them with spectroscopic observations. There is a very good agreement with deuterium observed in cosmological clouds, which strengthens the confidence on the estimated baryonic density of the Universe. However, there is an important discrepancy between the deduced 7Li abundance and the one observed in halo stars of our Galaxy, supposed, until now, to represent the primordial abundance of this isotope. The origin of this discrepancy, observational, nuclear or more fundamental remains to be clarified. The possible role of the up to now neglected 7Be(d,p)2\alpha and 7Be(d,\alpha)5Li reactions is considered., Comment: Invited contribution to the Origin of Matter and Evolution of the Galaxies (OMEG03) conference, RIKEN, Japan. Proceedings to appear in World Scientific